Recommissioning an R12 AirCon System

[enigmas]

NOTE: The information, images and videos below are provided purely for entertainment purposes. The intent is to give an overview of how an (aftermarket) R12 refrigerant underdash AirCon system can be recommissioned to viable operation in a Rover P5 Coupe.

(PPE)
Appropriate Personal Protective Equipment.
In the interest of personal safety as with any work on motor vehicles ensure that appropriate PPE is worn. When working on A/C systems wear goggles/glasses and rubber gloves to protect your hands and eyes from any sudden escape of refrigerant. It's not likely with due care, but it pays to be cautious in the event of frost bite.

Comments added at a later date to clarify various issues, devices and tech methods used in recommissioning this older model underdash R12 Aircon System will be added in a GREEN ITALIC font.

Overview
When I recommissioned my P5 MK3 Coupe many moons ago (it was re-engined with a Leyland P76 4.4 litre V8 amongst other things, hence this topic is in the Modified section.) During this time, I fitted an under dash AirCon system. The AC system was sourced from a Ford Econovan that I owned and later sold, obviously minus the AC. It's an after market (R12 refrigerant unit) utilizing a UNICLA compressor.

R12 refrigerant although a staple for car ACs up to about the 1990s (due to it's negative effects on the planet's ozone layer) is now illegal to use. It was and probably still is one of the most effective refrigerants for cars. Over the ensuing years its been replaced by several alternative types of refrigerant. One of the most commonly used and now slowly being outdated is RI34a as it's less harmful to the environment.

Discharging R12 refrigerant straight into the atmosphere is a criminal offence in OZ and the USA with heavy penalties applying. Most professional AC shops have recovery machines for this purpose. Recovery is normally free as R12 is both expensive and difficult to obtain. Interestingly it's still used and also available on the black market in some countries.

Moving on.
In OZ, unlike the United States, car enthusiasts couldn't legally (until relatively recently) recharge their car's AC systems. Tools and equipment to carry out this type of work was also costly and like other areas of car repair/maintenance shrouded in mystery and technical jargon.

In the USA both small handy sized cans of refrigerant (R134a) and the tools/equipment required to restore the viability of a car's AC were/are readily available at reasonable prices for DIY car enthusiasts.

If you can read, research where required, follow a methodical process and work in a safe manner, installing and/or repairing a car AC system is a viable option for a keen auto enthusiast.

With the aid of the Internet, Youtube and the vast amount of resources available via Ebay, as well as a legal use refrigerant for the DIY market, it's a straight forward option to recommission a seemingly old style R12 AC system in OZ.

Most if not all Rover cars up to the late 80's or whenever the mandated AC refrigerant gas changes were introduced, if factory or aftermarket fitted with an aircon system, would have used R12 refrigerant gas. These systems can now be made viably operational again at minimal cost and with a degree of efficiency comparable to that of the original R12 refrigerant. Neither the original compressor nor condensor need be changed. These older style systems were fitted with receiver/dryers and yes this component would need to be changed. These components are still available aftermarket and are inexpensive. I purchased 2 spares, both cost less than $40 AUD each.

Recommissioning & Recharging an Older style R12 AC system.
Here's a picture of the interior of my MK3 P5 coupe showing where the aftermarket UNICLA underdash A/C evaporator assembly incorporating the 3 stage blower fan is positioned.

[enigmas]

This is the refrigerant used to recharge my coupe's AC.


Below are several information sheets from the product supplier.

[enigmas]

The following AC pictorial schematics show 2 similar but slightly different systems. An early and later version.

Later more modern versions use a an alloy fine tube cross flow condensor. These are more efficient with R123a but can clog-up if the system is not maintained. Earlier versions (R12) use a serpentine flow condensor. These are still quite viable but not as efficient.

The earlier version (R12) uses the receiver dryer with a small glass sight window.
* Interestingly, newer versions are now re-introducing a sight glass again in their systems.

The early version shows the "receiver dryer" and the later version an "accumulator"


Later version shows an "orifice tube" and the early version an "expansion valve.


This image shows the circulation of the refrigerant in the car's AC system.


These images show the differences between a Receiver/Dryer and an Accumulator

[enigmas]

Fittings and Tools
An R12 system can be retro-fitted for use with current recharging ports and diagnostic tools.
These resources are all available today at very reasonable prices. Search the Web if interested.

Fittings
The charge/test ports on an R12 system are different to those of a more modern R134a system. There are 2 distinct lines. Low pressure BLUE. High Pressure RED

The port most often used is the Low pressure port.
Service caps designed to screw onto the R12 ports and accept modern gauges are available. New port fittings are sized differently, so cannot be confused or hooked up incorrectly.

These are the Fittings
Note the "schrader valve" inside the fitting. Virtually the same as a tyre valve.


These adaptors screw directly onto the R12 port fittings.

This is a set of AC manifold gauges.
These are used:
* To add the correct lubricant.
* To Devac the system (introduce and check the systems ability to hold a vacuum)
* To charge the system with refrigerant.
* To diagnose and check the system running pressures.


These are both Vacuum Pumps.
These are used:
* To create a vacuum in the AC system
* To remove both moisture and air from within the system

NOTE:
The Red unit reqiires an air compressor to function
The Blue unit is powered by an electic motor (240v in OZ)

[enigmas]

Tools & Lubricant

This is the specific lubricant used for the A/C when charging with Minus30 refrigerant.
Refrigerants require specific lubricants. The lubricant is required for the compressor and system functionality. Lubricant is moved throughout the system via the refrigerant. Lubricant types should not be mixed unless compatible. Not all lubricants are compatible so this requires a modicum of research.

This particular lubricant is compatible with mineral oil, the lubricant formerly used with R12 systems.

[enigmas]

AirCon Components

These images are of the ReceiverDryer, primarily fitted to older AC systems. They have a sight glass fitted at the top. The quality of the refrigerant can be discerned when the system is operational and viewing the sight glass.

The unit on the left is the original receiver dryer from my car's AC system. A new unit on the right. A receiver dryer also acts as a filter. Note the contents within. The small bearing like balls in the yellow container are actually a dessicant used to absorb any residual moisture in the system. They are located between the 2 circular screens within the dryer receiver.


The A/C schematic below shows the ReceiverDryer to the left and the manner in which the refrigerant enters and exits the unit.


Shown below is the AC System pressure safety switch (Binary switch) fitted to the ReceiverDryer.
The markings are in Bar units.
2 Bar = 29 psi (Lo Pressure)
30 Bar = 435 psi (Hi pressure)

If you turn the AC on and pressure is below 29 psi the switch will not allow it to operate.
Similarly if the pressure is Hi at around 435 psi, the switch will cut power to the compressor clutch effectively switching the AC off.



The above switch has a male fitting. There are also female binary switches. These can be removed from the receiver dryer without venting any refrigerent as they connect to a schrader valve fitting.

Female Trinary Switch.
These switches use 3 wires and will also turn on the condensor fan at a preset pressure.

[enigmas]

Charging the AirCon System

Below are the basic specifications for the AC compressor and system fitted to my Coupe.
There is a small silver label on top of the compressor stating these specs.


NOTE:
* The system was never recharged with refrigerant after initially being installed to my P5 Coupe.
* There was a minimal amount of original (mineral oil) lubricant remaining in the system as several new hoses and connections were required to plumb the A/C to it's new home.

An alternative refrigerant HychillMinus30 is being used, rather than the original spec R12 (now illegal)

Several easily adaptable changes were made to the hi and lo ports on the system.
See previous posts above.

Specific Changes made to the AC System are:
* New Hi & Lo port couplings.
* A new "synthetic" lubricant (compatible with residual amounts of original lubricant)
* HychillMinus30 refrigerant. (Replaces R12 or R134a refrigerant)



SYSTEM REFRIGERANT CAPACITY
Typical underdash unit for an average sized car.

134a - 22 oz

R12 - 28 oz

Hychill Minus30 - Use at 1/3 of the specified amount of refrigerant above.

NOTE:
The best method to verify that the AC has the correct amount of refridgerant is to check the running pressures of both the Hi and Lo Port Sides with a set of manifold gauges.

This is not a complicated procedure and will be outlined in the following threads.

[enigmas]

Testing the AC System for Viable Operation.
There are several methods to test an empty (no pressurized refrigerant within) AC system.
The accepted method is to charge the system with nitrogen. Nitrogen is an inert gas that is neither flammable or explosive.

But we're not going to do it that way as it's another associated cost.
If an air compressor is available that can reach 100 psi, then that will suffice. The idea is to pressurize the system to see if it will hold pressure and remain leak free, rather than charge the system initially and also introduce a dye into the refrigerant.
Using refrigerant and dye initially before checking to see if the system holds pressure may mean loss of refrigerant to the atmosphere. This is both costly, environmently unfriendly/dumb and unnecessary. I doubt most DIY guys have a refrigerant recovery machine at hand!

To test for 'air' leaks in this case soapy water will be used in a spray bottle atomizer in the ratio of 50% soapy detergent (car wash) and 50% water.

Note:
Air has moisture and some moisture may be introduced. Best to have a moisture filter/trap on the compressor as you would have for automotive paint spraying.
Compressed air is only left in the system long enough to locate any pressure leaks by using the detergent spray over connections and unions.

After air leaks if any have been located, air is then discharged from the system by depressing the schrader valve (looks like a tyre valve) on the lo side.
The system is then introduced to a vacuum (by virtue of a vacuum pump) for about 30 minutes. Creating a vacuum only takes a minute or so if the complete AC system is properly sealed.
The reason behind running the pump for 30 minutes is to remove any residual moisture in the system. Moisture boils off by virtue of the vacuum being created in the system.

PS.
The expedient of using soapy/detergent water and compressed air to locate leaks in an AC system is not mine but that of a professional I've been following who uses this method when circumstances require it, ie. A fully equipped workshop may not always be available.

[enigmas]

The AC Safety Switch.
Checking the A/C safety switch for Function momentarily.

The focus for this check is on an older receiver/dryer A/C system not a more modern system that uses an accumulator although a similar test can be done on these as well.

An early system such as the one being recommissioned generally (AFAIK) uses one pressure safety switch. This is generally fitted on Hi Side on a port of the receiver/dryer just below the sight glass. As stated previously, it controls both high and low pressure in the system and will override the internal cabin A/C switch if it deems the pressure within the system outside certain "safe"
parameters. Basically below 28 psi and above 400 psi.

Introducing Air Pressure to the system (Aim for 100 psi)
By introducing air pressure above 28 psi to the system the safety switch will allow current to flow through it to the compressor magnetic clutch.
When the clutch activates...a clicking sound will be heard.

NOTE:
The compressor clutch activating provides information that the electrical connections from the AC switch are all functioning.
For the switch to function the internal evaporator fan may have to be switched on as well. (This is what blows cold air to the interior of the car.) Some switches are combination types controlling both the fan speed and the A/C clutch operation.

The AC Relay.
Shown below is the 4 pin relay used and fitted to the underdash evaporator in my coupe.
Newer integrated AC systems in modern cars place these relays sensibly in an accessible fuse box in the engine compartment. This is not the case with the system in my coupe. If the relay is faulty the A/C won't function. Accessing the relay can be torturous if fitted in an inaccessible location under the dash or behind the evaporator under the parcel tray. Guess where mine is fitted?

Note the placement of the pins. This is not a typical generic type relay that I commonly use.
Fortunately I located a similar relay used on an aftermarket wiring kit.



Fortunately I located a similar relay used on an aftermarket wiring kit on Ebay.
I'll be extending the wiring and fitting the relay in an accessible location. The kit also provided a matching female plug and several metres of correct gauge wire. All for $25 delivered to my home, most likely from China. Now that's value. 😉👍

STOP PRESS. The wiring kit with the relay arrived today by courier. As my focus when purchasing the kit was primarily to locate a compatible relay for the AC I didn't pay too much attention to the details of the listing. On opening the package I noted that I had received not one, but two kits. Now that's a bit of serendipity.



The Relay Function.
This relay supplies the heavier electrical current to the AC Compressor Clutch activating it. But to do this it has to pass current via the Safety Switch. If the safety switch deems the pressure too hi or too lo then nothing activates as it should. But if the pressure is within the scope of operation the safety switch allows the electrical current through to lock up the clutch.

The safety switch operates on pressure. It's dumb, it has no idea what is creating the pressure. So for the intial test, compressed air is the medium used.

* The system compressor is only run for a few seconds. This is to test whether it functions or not.
On an old system there will be residual lubricant in the system. On a newly installed system, check to see that lubricant has been added to the compressor or whether you need to add a small initial quantity directly. This is generally what you would do if replacing a compressor. Some come prefilled with lubricant.

When checking for visual operation a helper is handy. Start the engine. Stand over the engine bay and have the helper/assistant momentarily switch on the compressor. If the clutch activates and the compressor operates switch it off. Test completed. The test should have taken a few seconds. Nothing is harmed.

[enigmas]

Testing for Leaks.
Hopefully the system is holding "air" pressure and that there are no leaks. This can be verified by using a (cheap) set of AC manifold gauges available on Ebay. The idea is to look for a pressure drop once the gauges are connected to the respective ports. Blue lo pressure port. Red hi pressure port. Interestingly if the system is in good order but not running, both the hi and lo side will stabilize at the same pressure.

Seen here.


That pressure will be whatever was put into the system. If you recall, compressed air at 100 psi was used. Similarly when a refrigerant is used the internal pressure will stabilize to the same psi across the entire system.

If there appears to be a small leak (slow or large drop in pressure as verified by the gauges) spray every union and connection with the atomizer container of soapy water. Bubbles will appear on the leaking joints/unions. Also look for fatigued and/or fractured/damaged hoses.

If the system appears leak free, then vent the system (of air pressure) by depressing one of the schrader valves on the lo or high side with a suitably small probe.

You are venting air not refrigerant so there are no issues to be concerned about.

If a leak was found, carry out the necessary repair then repressurize the system again and recheck for leaks. Repeat the process as often as required until no leaks remain.

I found one leak not within the system but on a gauge connection. So take your time and be mindful.

Method to Pressurize the AC System.
To do this I modified an old tyre pressure gauge by simply cutting off the end that attaches to the tyre schrader valve. This was then clamped over the end of the yellow line attached to the A/C manifold gauges. I'll improve on the method of attachment by adapting a suitable fitting at a later date.

Here's the old tyre pressure gauge.
The method of connection is quite obviously as can be seen at the end of the gauge hose.


It was hooked up to the end of the yellow line on these manifold gauges.

[enigmas]

Vacuuming Down the AC system.
At this stage in the recommissioning process the system should be leak free and able to hold a vacuum. Hooking up a vacuum pump is a straight forward process. There's a picture of 2 vacuum pumps posted earlier in this blog. The blue unit is powered by house mains electricity and the red unit requires a compressor to function. Both will do the job.

There are 2 videos below both well presented.
* The first video purely illustrates how to pull a vacuum on an AC system and identify whether the system has any leaks to the atmosphere. The presenter has covered every aspect of this process very thoroughly.

* The second video covers both the process of drawing a vacuum and charging an AC system. The presenter also mentions using teflon tape on the gauge connections but it my opinion, it's not necessary if the gauge set is in good order. No connections should ever be force fitted.




METHOD
AC manifold gauges are suspended above the engine in a suitable manner. The Blue line is hooked up to the Lo side port and the Red line to the Hi side port. The two couplings cannot be hooked up incorrectly as they will only fit their specific port. The yellow line is attached to the vacuum pump. The pump is then switched on.

Each port coupling on the manifold gauge has a circular knob. When attached to the ports and screwed (inwards) clockwise they will open the schrader valve. This is similar to depressing a car tyre valve. There are also 2 valves on the manifold gauges. These can be opening once the vacuum pump is working.

On a viable, sealed AC system at least 30 inches of vacuum will need to be pulled to ensure all the moisture is fully evacuated. Both gauge needles will move into the negative and show this. Leave the pump functioning for about 30 - 40 minutes to fully evacuate the system of moisture. After the time has expired, close both manifold gauge lo and hi knobs. Now take a break and come back in a few hours or perhaps the next day to see if the vacuum held.

If so, unscrew each knob (lo & hi ports) and remove the couplings.

[enigmas]

Adding Refrigerant to the System
This is what the refrigerant charging set-up looks like. To be explained with further detail later.



If recharging an existing system, decide on what type of refrigerant will be used.
If an A/C system is fully evacuated the choice is easier.
If the system is low on refrigerant but functioning, then topping it up with the same type may be the most expedient option.

Don't Ever Mix Different Refrigerants
Either fully evacuate the system or top up with the same type of refrigerant.

AC Lubricants.
Each specific refrigerant generally has a specific lubricant to be used with it.
Lubricant is carried throughout the system by the movement of the refrigerant.
Lubricant is required by the compressor and other components in the system.
Each system requires a specific amount of lubricant.
Lubricant details such as type and amount can be found on a label attached to the compressor.

* The specifications for the UNICLA System fitted to my coupe states: 4oz or 120cc of Suniso 5GS (mineral oil) with R12 refrigerant.

* As Hychillminus30 will now be the refrigerant used in the system (not R12), a compatible synthetic lubricant SRO500 will also be used.

* SRO500 is miscible with any residual mineral oil that may remain in the system.

Adding Lubricant to the AC System.
This is best done before pulling a system vacuum for 30-40 minutes as previously outlined.

Method
Note: This is done with a completely depressurized system.
Using the manifold gauges hook up the Blue hose to the lo side port.
Screw down the knob on the Blue coupling to open the schrader valve

Uncouple the Red hose from the manifold gauge so that it is completely detached and attach the coupling end to the hi side port.
Screw down the knob on the hi side coupling. This will open the schrader valve.

Attach the vacuum pump to the yellow hose

Pour the prescribed amount of lubricant into a small container.
Immerse the other end of the Red hose into the small container.
Turn on the vacuum pump and open the lo side knob on the manifold gauges.
The vacuum (suction) created by the pump will draw the lubricant in through the Red hose into the system.
When all the lubricant is drawn into the system, switch off the pump and detach the hoses from their respective ports.

Reattach the Red hose to the manifold gauge and close both manifold gauge knobs.

Job done, lubricant added. 😎👍

After the lubricant has been added, it's time to pull a vacuum on the system for 30-40 minutes.

[enigmas]

Charging the System with Refrigerant

WARNING
* This relates to charging the A/C System with the ENGINE RUNNING.
NEVER open the Red Hi Side knob when charging the A/C System with refrigerant.
Ensure that the Red Knob is fully closed before starting the charging process.
Doing so, can and will (when the compressor cuts-in) over pressurize the refrigerant charge bottle leading to the container rupturing or worse.

Appropriate PPE.
Wear goggles/glasses and rubber gloves to protect your hands and eyes from any sudden escape of refrigerant.
This is not likely, but it pays to be cautious in the event of frost bite.

Having pulled a vacuum in the system once again, it's now time to recharge it with refrigerant.
For my coupe's A/C system the refrigerant of choice will be Hychillminus30.
The amount of refrigerant needed to charge the system will be approximately 1/3 of the original amount of R12 refrigerant specified for this system.

The amount and effectiveness of the refrigerant charge will be verified both by weight in grams (using a digital scale) and also by observing the pressure within the system on the manifold gauges.

To charge the system the A/C will be switched on (evaporator fan on maximum and the engine running) As the refrigerant charge enters the system another indicator will be cold air blowing through the evaporator vents in the car. If desired, a thermometer can be positioned in or near the vents to register the drop in air temperature. This isn't really necessary though as the cold air can obviously be felt. If you really need to know then insert an appropriate thermometer into the evaporator air vents.

[enigmas]

Prefacing Comment
Work on the AC in my Coupe was for the major part completed a couple of weeks ago. There are still, as yet, a few modifications I want to make to the system to improve the driving experience when the AC is operational.

One such feature will be to incorporate an adjustable "vacuum sensing/electrical control switch."
This switch will automatically disengages the AC clutch whenever there is a need to accelerate quickly or when the engine is under a specific load, for instance climbing a steep gradient.

Method of Setting-up to Charge the AC System

[enigmas]

SWITCHES: AC Vacuum Control Switch & A/C Thermostatic Control Module.

This is the "Adjustable Vacuum/Elect Switch" below and a brief piece of tech literature on the device.
The switch will be utilizecd to cut power to the AC compressor clutch whenever there is a requirement for immediate acceleration. This effectively removes the load of the compressor from the engine at these times. Once back on light throttle the A/C will cut back in again.





The Thermostatic AC Controller

This next device will thermostatically control the "set" temperature within the Coupe's interior by automatically switch the AC (via the compressor) on and off.
The device actually has 2 relays one to control the AC clutch and the other to control the heater.
Unfortunately the second option isn't really viable as the P5 has cable control for the heater coolant inlet valve, as I really don't want to reconfigure the heater function with electrical solenoids and any other switching that may be required.

This is the A/C thermostatic controller.

[enigmas]

Checking the AC System Refrigerant Charge.

To clarify, I'll briefly recap what was done.

* The A/C system had no refrigerant within it for over 30 years.
* When custom fitted to my P5 coupe new A/C high pressure hoses were fabricated.

* To recommission the AC system a new "ReceiverDryer" and "Hi/Lo Pressure Safety Switch" were
fitted.

* All the hoses and connections that are accessible were checked.

* The system was then pressure tested with compressed air prior to fitting a new receiver/drier.
Note: A professional AirCon shop would ideally use "nitrogen" for a system pressure check and to also gauge for any system leaks, but not all shops do, so don't hold your breath on this procedure.


100 PSI is more than enough air pressure to trick the safety switch into operation.
28 PSI is the low pressure cut off point for the safety switch.
The switch is dumb, it doesn't know what is creating the pressure, air or refrigerant.

* Lubricant (synthetic) of the correct quantity/type was added to the system after releasing the
air pressure.
Release the "air" pressure at the Lo Side schrader valve and inject the specified amount of
lubricant with an injector device/syringe.


It can also be drawn/sucked into the system on the high side by attaching the vacuum pump on the
lo side.

* The system was then connected to a vacuum pump to see if it would maintain a vacuum of 30 inches.
Manifold gauges need to be hooked up to the Lo and Hi Side ports to confirm this.

* After confirming the system held a vacuum, it was recharged using an environment friendly
refrigerant (hychill minus30).

* Note:
The system originally used R12 refrigerant and mineral oil lubricant.
R12 is a very effective refrigerant but is harmful to the environmemt.
Minus30 refrigerant is not a fluorocarbon but a hydrocarbon.
It has negligible impact on the environment but as a hydrocarbon it is highly flammable.
For safety, recharge an AC system with Hychill30 in an open environment free of ignition
sources.

Method.
With a vacuum within the system connect the manifold gauges to both the hi and lo side.

Hi Side connection can just be seen below the power steering reservoir. Look for the RED knob


The BLUE Lo Side is easier to see.


Open the valves on the 2 ports by screwing the knobs clockwise.
Keep the hi side gauge knob closed at all times during the charging process.
* Start the engine and turn on the A/C and blower fan if it's not automatic with the A/C switch.
Older underdash units like mine had independent switches for these 2 functions


Adding/Recharging Refrigerant to the System.
You will need to know the quantity of refrigerant for your system.
For the AC system fitted to my coupe when it used R12 refrigerant, it was 794 grams or 28 ounces.
NOTE: Minus30 uses 30% less refrigerant. So that's 265 grams or 9 ounces.

Running pressures as observed using the manifold gauges are also considerably less.
Look for 20 to 40 psi on the Lo Side and 150 to 225 psi on the Hi Side.
These are the running pressures of my Coupe's A/C on a 70°F day.



Use of the Scales
With the gauges hanging from a suitable support, hook both Lo and Hi side lines up.


Ensure the valves on the gauges are both closed and hose connections are firm.
Hook the refrigerant bottle up to the yellow hose, but do not open the refrigerant bottle valve.
Rest the bottle with the yellow hose attached on a set of digital scales.
Read off the weight of the bottle on the scales in grams. A section of yellow hose will also be included in the total weight as it is attached to the bottle at one end.
Record the weight.
For example, if the total weight is 1000 grams and the required amount of refrigerant for the system is say 400 grams, then once 600 grams is indicated on the scales by virtue of charging the system, the job is done.


Note you should also pay attention to what pressures are specified for both the Lo and Hi sides. These pressures vary with both the type of refrigerant used and the ambient temperature on the day.

READ the Spec Sheet for the type of refrigerant you will be using.

Now that we've setup to charge the system with refrigerant start the engine and turn on the AC and the internal evaporator fan to the middle setting.

With the engine running and the AC switch turned on open the valve on the refrigerant bottle.
If similar to the one shown in the picture below screw the valve slowly inwards in a clockwise direction.
This pierces the cap seal and releases the refrigerant into the yellow hose.

Where the yellow hose attaches to the gauges there is a small cap with a schrader valve under it.
Remove the cap.
With the end of a screwdriver lightly press in the schrader valve for a second or two to expel any air in the line.
Air carries moisture. Moisture affects the AC system negatively.
Refrigerant should issue out momentarily. This is legally permitted.

The engine is now running, the AC is switched on but the compressor clutch hasn't as yet activated.
Slowly open the BLUE manifold knob on the gauges.
Refrigerant will now enter the system as it still maintains a vacuum.

Once a specific amount of refrigerant enters the system, generally about 28 PSI (2 bar) of pressure, the AC Safety Switch will activate and allow the compressor clutch to lock and drive refrigerant through the system.

The A/C is now starting to function and cool to cold air will issue from the evaporator inside the car.

WATCH THE MANIFOLD GAUGES CAREFULLY. Also pay attention to the scales and how much refrigerant is entering the system.

Close the BLUE Lo Side valve on the gauges when the targeted pressure is close to the specifications for the refrigerant being used.

IDEALLY YOU DO NOT WANT THE PRESSURE EXCEEDING THE RECOMMENDATIONS ON THE REFRIGERANT SPECS.

This is not as dramatic as it sounds as small amounts can be bled off via to Lo Side Schrader valve if necessary.

OVERCHARGING does not improve the efficiency of the AC system.
It is more likely to stress the system and compromise the compressor shaft seals.

Base you final judgement on the GAUGE READINGS as they reflect the system in operation.

When satisfied close off the refrigerant bottle valve and bleed the yellow hose at the schrader valve at the gauges to release remnant refrigerant from the yellow hose.

Screw out both valves on the Lo and Hi side, then you can remove the couplings.

Refrigerant Cannister Tech.
On some types of refrigerant, the manufacturer may want you to rock the bottle back and forth 45° each way from vertical, whilst others may specify inverting the cannister whilst charging the system.

NOTE:
Generally AC compressors are designed to compress gas not a liquid. Compressing a liquid can cause an hydraulic lock (liquids are not compressible.) This can wreck an AC compressor. Inverting a refrigerant container is just a quicker way of recharging a system. Rocking the container back and forth assists the process with AFAIK no negative repercussions.

Read the literature, study the method and make a choice.

Hychillminus30 specifies inverting the refrigerant container. I didn't use this method and it worked fine for me by simply rocking the bottle gently back and forth over a 90° arc.

Pressures Equalizing in the A/C at Rest
With the AC system switched off and let to rest for a while (and with the manifold gauges still connected) it will be observed on a viable system that the overall pressure within the system will stabilize throughout.
Note:  Both gauges (Hi and Lo Sides) have stabilized at 100 psi. 😎👍



A Normal Functioning System using Hychill Minus 30 Refrigerant

[enigmas]

Other Related Tech Info
In no particular order.

Temperature Pressure Chart


Diagnostic Gauge Readings


Normal Functioning System


Rule of Thumb

[enigmas]

Thermostatic Temperature Control Module
It finally arrived today. Ordered via Ebay, but in reality all the way from China. At $25 AUD (postage included) this compact piece of tech is remarkable and great value.

Although I posted a few images of it before, here are a couple more pix to help refresh memories of the component.

This first pic shows the relative size in relation to a matchbox.


This pic shows the very basic wiring required to connect it to the A/C in my Coupe.


The unit has 2 small relays built into it. I'll only be using one to power another relay that will do the heavy current switching to activate the AC compressor clutch as required.

The other part of the component, the black cable that can just be seen is the temperature sensor. It has a small metal cap on the end of the cable. This will be positioned in the area of the parcel shelf, most likely underneath it.

The wiring to the module is very straight forward as can be seen in the diagram shown in the second image.

The module is designed to sense the internal temperature of the car. Based upon the given setting, the module should turn the AC unit on and off to maintain a specific temperature within the car.

* The only other and last component that I'm now waiting on to arrive is the adjustable vacuum switch. This is the device that will automatically disengage the AC compressor whenever fast acceleration or a substantial load (hill climbing is imposed on the engine.

[enigmas]

Wiring in the Climate Control Module.
I spent about 3-4 hours wiring the module up to the AC system today.
Part of the plan is to incorporate the original AC switch so that it doesn't become redundent.

Briefly, the original AC system uses a combination rotary switch with 2 functions on a common stem.


The upper most knob (marked with the White line) has 4 distinct positions and operates the internal blower/fan.
The positions are: Off, Low, Medium and High.

The rotary switch (marked with a Blue dot) directly underneath the blower switch, controls (or is supposed to) the magnetic clutch on the compressor.
The switch is a variable resistor. Zero volts at one end of operation and 12 volts at the extreme other end.

There's a graphic image under the switch that I believe is meant to illustrate the AC "cooling" range, going from cool to cold air. It really never made any logical sense to me, as unless the compressor clutch received a full 12 volts, it wouldn't engage. So the knob always needed to be set at its maximum level.

Making use of the former AC Rotary Switch
As I'm now using a small electronic temperature sensitive control module that reads the ambient cabin temperature and automatically switches on the AC when the "SET"" cabin temperature rises above 24°C or 75°F I've wired the resistance switch in series to act purely as a power Off or On switch at it's extremes of operation. For this to occur though, the ignition must be switched on to provide an initial power source. The blower/fan though, can operate independently from the AC if desired to purely circulate ambient temperature cabin air.

The Temperature Control Module "SET" temperature is adjustable in degree increments (up or down) to achieve any desired "cooling" temperature within the interior of the coupe.

Issues
The only frustrating issue with the module was deciphering parts of the instruction sheet that dealt with setting the operational parameters with regard to adjusting the settings. The Chinese version of English grammar on a set of instructions can be a bit frustrating, but apart from that, the simple graphic wiring-up diagram is very easy to follow.

To ease matters in the future when/if I want to alter a couple of settings, I'll write up my own set of basic instructions.

For anyone that may be interested in using this type of module with an older style AC system here are the supplied instructions.




Tomorrows task will be to securely mount the module in an appropriate spot and locate the temperature sensor in a suitable position.

[enigmas]

Fabricating the Mount for the AC Module
Fabricating this mount has taken more time and effort than I initially considered. This is generally the case with any modification as often the seemingly easy and smaller tasks tend to consume more time.

I didn't want to cut an opening into any areas of the dashboard facia so decided to place it below the binnacle pods on the RHS of the coupe. This is also the location of the LPG/Petrol change over switch as the car is dual fuel. I eventually decided to incorporate it just below this cluster of instruments. Tucked away here the module is relatively discrete.

Construction.
I had a piece of stainless steel sheet aside and it seemed like an appropriate material to fabricate a mount. Easy to bend and weld.

Here are a few pix of fabrication process. No exotic tools were used just what I have at hand.
A cardboard template on the left and a piece of stainless steel sheet to the right.








The module fits into/between the shoulders of the mount. A piece has still yet to be fabricated that will strap the module to the mount.
There are 2 small tabs in the next photo that show the securing points for the strap.


I do have a  spot welder and that made joining small pieces and tabs much easier.

[enigmas]

Mount Fabrication_Part2

I spent several more hours today fettling the mount and adding an internal brace. Just a heavier piece of sheetmetal laminated to it using a spot welder. This more than doubles the thickness on a section of the mount. The stainless steel material I used was easy to manipulate but allowed too much flex without having 2 opposing securing points. I wanted to avoid a second mounting point as it eases access the instrument pods on the drivers side if any maintenance is required.

The mount is designed to be held by the steel rail directly underneath the padded rail in front of the parcel shelf. As such it has to be fairly resistant to flexing.

The Module's Wiring
All the wiring has been taped together into one long lead and although currently connected, will need to be cut near the original AC switch. A small electrical connector plug will be wired up. The module will then be fully removable as a unit (if need be) but more importantly, the lead can then be rerouted behind the module between the DS parcel shelf, the steering wheel cover and then under the parcel shelf to it's original connection point.

Here are some pix of the finished mount, not as yet painted (in satin black) but properly located. The wiring lead (seen hanging down) will be relocated as outlined above.

The yellow pieces shown are artist mountboard hot-glued to provide a level mounting surface for the module. The card will also protect the module and mount from chaffing other contact surfaces.

[enigmas]

Finishing off Wiring the AC Controller Module

Oh joy, I've virtually (unless something goes askew, cross fingers) finished wiring up the A/C module today. The wiring was re-routed behind, then under the parcel shelf at the rear of the steering column cover on the RHS, then back through a small access hole under the shelf and then over to the switch gear just to the left of the steering column surround under the padded vinyl ledge that is positioned in front of the parcel shelf. It couldn't have been simpler if I'd worked at Rover in the day and helped in designing the wiring loom! 😕 I'm glad I didn't have to access any wiring within the instrument binnacle...been there done that too, rather not go there again if it can be avoided.😉

Connecting the wiring
A small 2 pin male/female plastic connector was used to reconnect the wiring. The hardest part of the job was fitting the tiny components to the wires under the parcel shelf. These had to be soldered and then orientated correctly so that they'd lock into their respective tiny connectors. An easy task if you have 20/20 vision and were of a similar age. The wires were then tucked up, away and out of sight.

Here are a couple of pix of today's task.
As an aside, the module is fitted with a temperature sensor. The sensor is a long thin wire with a small metal cap at its end. It's just visible in one of the photos below.

Can you spot it?

[enigmas]

Bringing it to a Conclusion.

For those individuals that have shown some interest in this blog...and yes, it is coming to an end. 😉 The primary reason I started this A/C blog was to see if I could recommission an older style car AirCon and to also whilst doing so, add a few improvements as to how it functioned.

An A/C system similar to the one retrofitted to my P5 Coupe was what would have been fitted to a P5 in the day. Probably moreso to a P5B than a 3 litre, simply be because I believe they weren't optioned earlier. But truly, there's no reason that a modern aftermarket "Vintage AirCon System" (that's actually an AC manfacturer brand) couldn't be fitted to a 3 litre P5.

Fitting an older style single or twin piston (1960 - 70s) compressor though, really wouldn't make sense. Older style compressors really do load up an engine. Any of the modern compact compressors (used on smaller engined cars) work fine and could easily be adapted to an older A/C system.

If you're handy...it's all available at minimal cost at auto wreckers. Hoses would need to be made to suit the application and obviously some pipe work altered. But all the required, larger item components are there. Most cars today are fitted with A/C, so the selection of parts is huge. All eventually get crushed and recycled whether they have been stripped of parts or not.

Moving on....

[enigmas]

Fitting the Vacuum Switch.

The vacuum switch is the final component that I wanted to add to the AC system in my coupe.
I received it in the mail, all the way from the US about a week ago. It came in a package about the size of a house brick yet it could fit into a match box? More than likely being screwed on shipping costs!

Here's the switch below together with it's package, instruction sheet, 2 small spade terminals and a tiny allen key used to adjust its function.
The switch's primary purpose is to control lockup on an automatic transmission's torque convertor but obviously can be used for other purposes.




Why use this Vacuum Switch

The primary reason for using the switch is to turn off the AC compressor clutch automatically and instantly whenever the need for full engine power is required.
Engine vacuum levels are a good barometer of engine health and also indicate when it is under a heavy load or just cruising along with minimal load. If observing a vacuum gauge whilst driving a car, a lot of valuable information can be gained. For instance, there's a significant drop in engine vacuum upon hard acceleration or when working against a heavy load such as climbing a steep gradient.

Below are some pix of brief notes that I use for reference purposes when wiring up these little specialty devices.


The vacuum readings noted above are taken directly from the engine in my coupe.

Below is the wiring schematic that I'll be using with the vacuum switch.

* For the purposes that I'll be using the switch, the COM terminal will be power-in from the AC Control Module.
* At 15"HG of engine vacuum or more, the switch will trip across and feed power from to the NC terminal to the NO terminal.
* The NC terminal is used as a dead power output and is not connected to anything.

The vacuum switch overrides all functions of the AC compressor (via it's magnetic clutch) based on engine load. It does this by cutting power to the AC relay.
The A/C relay directs power to both the "Compressor Clutch" and the AC "Condensor Electric Fan" (not at this time fitted.)

* Briefly, both the AC and the Electric Fan (that provides additional cooling for the Condensor) are automatically switched off at an engine vacuum reading of 15"HG or less.
* The vacuum switch effectively overrides and switches off the compressor clutch when extra engine power is required.


Electrical Switch Symbols

NO = Normally Open
NC = Normally Closed

* The reference to "Normally Open or Normally Closed" defines the switch function at rest, when not activated.

For example:
A NC switch will pass an electrical current until activated.
A NO switch will not pass current until activated.


Why a Setting of 15"HG of Vacuum.
For the moment it's just an arbitrary setting, a guesstimate that will be tweaked as needed when the car is driven in varied road and traffic conditions.

[enigmas]

Mounting and Connecting the Vacuum Switch.

There were 2 options for this:
* Mount it inside the car near the instrument pod fitted with the vacuum gauge.
* Mount it in the engine bay in a suitable and accessible space.

I decided on option 2, as both the AC relay and a suitable vacuum source was close by.
It would also simplify any vacuum adjustments to the switch, if needed.

A few pix below show the small mount that was fabricated for the switch and where it was positioned in the engine bay.


The vacuum switch is mounted to the left of the AC Receiver/Drier. The AC relay can be seen just below the coolant header tank.


Below are the small vacuum lines that provide a vacuum signal to the AC vacuum switch and the MAF sensor of the programmable electronic ignition system that the car uses.