Patient A/C Coaching Needed


For the first decade of owning XJS’s I was too intimidated by the seeming complexity of the V12 to attack anything but the most rudimentary issues of the car. However, coming off my now successful forays into overhauling the cooling system, diving into Death Valley for plugs, wires, etc., replacing the steering rack, and other tasks with all of you expert's assistance; I’m trying to screw up the courage to go after something I’ve ignored for at least 5 years.

The A/C hasn’t worked, but this has been easy to overlook because I almost always only drive the car if the top is down. The only times I truly miss the A/C is ironically in the winter when we get rain. Though it was nice if you stopped at a light with the sun beating on your face to have the cool breeze, so I thought I should at least figure out why it’s not working. Then I can figure out if I can fix it and how I should fix it.

There is something about A/C stuff that I make overly complex or I fear messing up or doing something dangerous. For some reason the XJS climate control system seemed like voodoo magic to me even when it worked. Also I’ve researched this topic several times over the last year, and read nearly every thread on the forum, and read the Delanair III manual Doug posted, but there is so much conflicting information that I’m more confused now than when I started. However, I intuitively know it can’t be that hard, and I’ll just need help over a few hurdles.

So if some you experts would be so kind as to help me out step by step, and maybe bring clarity to some of the issues I don’t understand, I would be very grateful. It will require lots of patience and tolerance of stupid questions. I’ve got a really packed schedule so it might be a week or two between steps, and I’ve got an intermittent issue on the X350 I’m trying to pinpoint as well.

The system is untouched from stock, and I don’t believe it ever required recharging prior to it not working. So it’s still the original R12 system. As far as I can tell the clutch isn’t engaging on the compressor, but I don’t know if it’s electrical or too much freon leaked out so the clutch won’t engage.

I have a set of A/C manifold gauges that I’ve only had to use once since I bought it. On one of our other cars I suspected the PO had overcharged the system and wanted to learn how to check it (he had overcharged).

I thought perhaps the first thing I should do is put the gauges on the system and check if there’s any pressure in the system. The r134a fittings are separate and screw onto the hoses which look like the old type R12 hoses, but I don’t know for sure. It’s Harbor Freight R134a unit. Can I use this to just test if there is any pressure in the system?

One other thing I’ll have to address is that the lefthand blower motor won’t shut off and I had to pull the fuse so it would run not down the battery. However, I thought I should wait on that problem in case I eventually have to tear into that area of the car anyway (gawd I hope not).

Please don't say, "take it to a A/C shop." I either want to figure this out myself and learn, or I'll go back to pretending I don't care if I have A/C or not.

Thanks everyone.

 

The first step is to check the system pressure. Yes, the hoses screw onto the R12 fittings without the R134 adapters. Wear gloves and do it fast once you have the threads started, as if there is gas in the system under pressure it will leak out and be cold due to the pressure drop. The gloves protect your fingers from the cold.

Make sure you have the low and high side hoses on the correct side, as R12 fittings are the same on both. Also make sure the valves on the gauge set are closed before connecting it to the car.

I think you'll have a pressure switch on the back of the compressor, earlier cars had a superheat switch. Both provide protection to the compressor from low pressure and will prevent the clutch from engaging. I think you need ~35-40 psi in the system before the clutch will engage. If you have less that that, then you have a leak somewhere and need to fix it.

A very common place to leak on the GM A6 compressor is where the hoses attach to the back plate. There is a bolt that goes through the centre of the hose retaining plate to hold the hoses against the compressor. As the bolt is tightened, the plate bends slightly and it doesn't hold the hoses square against the O rings and they leak. The solution is to go to a junkyard ( or maybe Ebay?) and find the plate from a GM car from the 70's or 80's. The GM plate is twice as thick as the Jaguar plate and doesn't bend. Replace your O rings while you are in there.

If you are going to do your own AC work, you should also get a vacuum pump in addition to the gauge set, plus a small meat type thermometer and a can tap.

Once you have checked your pressure report back and we can guide you further.

AC isn't a black art, I find it fairly simple and straightforward. You can google for descriptions of how AC works on a conceptual level, all it is is making a fluid change state from liquid to vapour and back. One process takes heat to boil the liquid, the other gives up heat as it condenses. Once you know the basics you can reason your way through the system to know what is happening where and why.

 

Thanks. I have a vacuum pump though I've not had a chance to use it. I have an InfraRed Thermometer will that work?

My thinking is that if there is no pressure in the system, then I need to convert it to r134a (which raises all sorts of questions). If there is pressure, I don't want to be opening things up in my garage.

 

The first thing is to recognize and remember that, while the *control* aspect of the system can be tricky, the *refrigeration* part of the system is plain as mud. Sure, you still need to know what you are doing....but there is nothing exotic about it. Compressor, hoses, evaporator, condenser, expansion valve....just like a million other cars.

Jagboi already gave you a good start.


Almost certainly a problem with the relay/diode/circuit board mounted inside the blower motor case. If that's the case I'm afraid it isn't a pleasant repair, sorry. Getting the blower motors out for the repair (see the link below) is not fun. The actual electrical repair is pretty easy once you have the blower assembly removed.

Air conditioning blower control


Cheers
DD

 

[sigh] Yeah, I guessed that would be the case... fun times ahead.

 

You'll need it for measuring vent temperatures, IR thermometers don't work well for that. The cheapie Wal Mart (et al) cooking thermometers work well.

 

There are ways around having to convert. We can talk about that later if need be.

Obviously you'd never open a system under pressure. However, if there is no pressure (or essentially nothing) that's a different situation.

 

To confirm, the high side is the one further to the car's right on the thing that looks like a muffler by the compressor, and the low is on the left side hose going to the fuel cooler. Correct?

 

Also don't I have to connect the hoses using the end with the valve depressor so it opens the schrader valve?

See picture attached

In the Harbor Freight instructions, they show those ends going to the manifold. So it's a little confusing.

 

Correct. If you don't put that depressor in, nothing happens.

Take a look at your brass manifold. On mine there is nothing where the hoses attach, just a hole for gas to pass through. No schrader valve on the manifold end.

 

Likely to no one's surprise, hooked up the manifold and there is zero pressure.

 

No hiss or anything when you connected the hoses? If you depress the schrader valve on the car with a screwdriver tip there is nothing? Just want to double check.

Assuming so, then you have a leak. Next is to find it. Just on general principals, I would remove your cruise bellows and then the hoses on the compressor. Check the retaining plate for flatness ( I bet it's warped) and replace the O rings. I would also replace the schrader valve stems. You'll need a special tool to unscrew them. Parts stores often have the O rings and stems, or if you have an AC supply close they might have them. I'm assuming you have the GM compressor ( about 12" long and round?). It's generically known as an A6 and has been around since the 60's, so O rings are standard items.

 

I missed this initially. Yes that should be correct. The larger sized hose is low pressure vapour returning to the compressor from the fuel cooler and expansion valve on the firewall, the high side is the smaller hose which carries high pressure vapour going to the condenser.

 

Correct. After removing the hoses, I double checked by manually depressing the schrader valves. Nada.

 

So at this point you have a major leak. I've tried all three ways depending on the car and the severity of the leak:

Pull a vacuum and see how long it holds and if you can hear any hissing that would identify the leak source

Use shop air (with a regulator), and pressurize the system. Soapy water and bubbles may help identify the source for the leak

Use a can of refrigerant with dye - needless to say this is best suited if you have a small partial leak and the freon cops will send you to Gitmo for water boarding yada yada. The dye is good for catching leaking o rings and an electronic sniffer is great for sniffing recessed and unaccessible areas.

In most cases, the leading causes will be:
Expansion valve
The seals on the rear of the compressor as previously mentioned by others
Leaking valves on the refill ports

My XJ12 had all 3, I fixed the first and last, then cooler weather set in and I never got around to replacing the GM A6 with a Sanden which was the recommendation if you favor a modern light and efficient compressor over originality.

If anybody has a part number or US supplier please post up.

 

All in this thread:
https://www.jaguarforums.com/forum/x...pgrade-126362/
Greg

 

Thanks Gentlemen,

I couldn't tear into removing the bellows today because of a lack of time, and having an extra driver around I need to keep the entire fleet running this week.

However, I did pull vacuum on the system and listened for leaks. There is a definite hiss at the compressor and possibly at the fuel cooler front union (though this could be reflected sound from the compressor leak).

When I did all the research I was leaning toward the following in the event the system had leaked out all the R12:

1. Instead of worrying about getting all the mineral oil out of the A6, upgrade to the smaller and more efficient Sanden type already set up for r134a.

2. Replace the Receiver/Drier (they are widely available now for less than $20)

Does that make sense?

 

Just to toss out another option.....

These aluminum A6 compressors seem to have caught on as well. Lighter and supposedly better performance than the original A6s ...and the convenience of a true 'drop in' replacement. About $225-$350 depending on where you shop.

Four Seasons Air Conditioning Compressors 58096 - Free Shipping on Orders Over $99 at Summit Racing

Cheers
DD

 

I had bookmarked that thread, but wanted to ask you exactly what you meant by "straight replacement". Does it bolt in without modification? Do the A/C lines connect without modification? Do the electrical connections work without modification?

Thanks very much.

 

I'm very interested in hearing all the options I should consider.