Multiple issues that I can't figure out. Hope you folks can help, as it DOES get hot in Northern Wisconsin!

1. The compressor doesn't turn on. My limited experience on other auto A/C systems has been that even if there is a very low refrigerant charge, the A/C compressor will cycle on/off. This does nothing. A/C relay is good.
2. The heater control works, and opens the valve.
3. The fan works at all settings, and when turned to "defrost", flaps move and airflow changes to the windscreen.
4. No setting causes air to come out the "face vents". The vents on the far left and right are good.

Any suggestions?
Thank you,
GrandpaDan

 

A very low refrigerant charge will disable the compressor clutch.
The pressure switches are designed to keep the compressor from damage if no refrigerant and/or OIL.
Gauges will give some indication of charge level.

 

Normal behavior as Bob says above. Face vents only open when AC is blowing, otherwise closed.

You can use a fused jumper at the AC relay to momentarily test the operation of the compressor.

 

There is usually a pressure switch close to the receiver/dryer. If you disconnect it and jumper the wires, the compressor should kick on. If it does not, you have a deeper problem than low refrigerant.

 

I jumper'd the #30 and #87 terminals on the relay, with no clutch engagement.
There is a pressure switch on the back of the compressor, and when I jumper that, the clutch engages.
I don't have a set of gauges, just the gauge that is attached to an R134a re-charge can, but the "resting" pressure on the low pressure side is about 40psi at 80F.
When running with the compressor clutch engaged, the high pressure hose gets hot, while the low pressure hose stays about ambient.

 

If you truly want to analyze and maintain the AC system yourself, my advice would be to invest in a set of gauges, a vacuum pump and a UV flashlight. All very affordable on eBay or AliExpress.

I'm assuming the system has been converted to R134A?

 

Yes, one of the PO's had it converted.
I've ordered a set of gauges and a vacuum pump. I usually don't buy a new tool unless I have at least 3 projects that need it, and I decided, with 2 other car projects on hand that it was time to tool up and learn a new skill.

I think there is some sort of "control" problem, but I should be able to bypass the controls and make the A/C system work, and then focus on the control.
Thanks for all the help. I'm persistent...I'll win in the end.
GrandpaDan

 

If it's any consolation, about 15 yrs ago I was in the same position as you are.

I knew even less about AC than you do and when I took my car to an auto AC "expert" he told me the compressor wasn't running so I was looking at least 4 figure repair. Then one of my mates who knew a bit about AC told me the compressor wouldn't run if the system was low on gas and proceeded to push in the schraeder and a hiss of gas came out.

That's when I decided to learn about AC. Went to a dark spot with a UV flashlight and found my condenser was leaking. Repaired it with JB weld and got a new rec/drier. Then I bought the vac pump, gauges and other bits and pieces and fixed it. Still blows ice cubes to this day although I did swap refrigerant to R152A a couple of years back.

 

Not knowing enough about the system we are getting fixed always puts us at risk of some mechanic unleashing the parts-cannon on us so I always try to understand how the system works.
I've done simple things to keep my A/C systems going, but there is always a point where I have to take it in, because I don't have the equipment to DIY. That's going to change, and this repair will more than pay for the gear. Plus, I have the freedom of making my own schedule to do it.

This is a rural area, so taking it in anywhere near me gets an automatic heavy upcharge because it says "Jaguar" on it.

I appreciate your encouragement.
GrandpaDan

 

If you would like dealer info, Service Training from my collection of guides.

 

My gages and pump arrived, so myself and my brother are going to learn what we need to know to fix the Jaguar.
We both in our 70's, so it will be a test of "can old dogs learn new tricks?"
It's going to be 90F here today, with a heat index of 98F, so this new skill would be pretty handy!

Thanks for all the help!
GrandpaDan

 

After a lot of youtube vids, and experimentation...we determined that there was no refrigerant in the system.
We pumped it down for about 15 minutes, and it has held that vacuum for hours.
Our question is: Where did it go? My best guess is that the r134a conversion connectors are leaking, and it won't show up until the hoses are off. I'll replace the valve cores and pump it down again.
This is kinda fun, tbh.
GrandpaDan

 

If you REALLY want to find out where it went (connector valves are common leak points BTW) buy a LED UV flashlight (Ebay) and go to a dark place and shine it around the AC components. Leaks will brightly fluoresce.
Not a bad idea to pick up a 2oz. dye/lube gizmo at Autozone or O'Reillys and put a shot in with the new gas charge.

That way, if it leaks out again you'll be able to see the trail.

 

Something like this kit will help find leaks.

https://www.ebay.com/itm/30573930974...3ABFBMzv2x74hm

 

The system had dye added when serviced 2 years ago. I have a UV light from an earlier project finding an oil leak in a 91' Blazer. I got a glow around the high side port.
I put in about 10psi of a special blend of 78% nitrogen, 21% oxygen and 1% trace gases, otherwise known as "air". I soaped up the connectors and found a leak on the high side fitting. Vented the air out, blew out the fittings with more air, replaced the valve core and pulled a vacuum of -30 for 30 minutes.
I'll give that some time to show any leakage, while I get ready to charge it up.

The notes from the service a couple years ago said "2.5lbs" of r134a was used. That seems high. I'm going to put 32 ounces in...does that sound ok?

Thanks!

 

A 'rule-of-thumb' is to add 80% R134a if the system was R12.

 

Put a thermometer in the side vent and once the compressor kicks on, start looking at the thermometer. Once you're close to getting the recommended amount of refrigerant in, add the refrigerant in small bursts of a second or two and look for your target cooling temp on the thermometer. Don't go over or it'll start getting warmer.

 

We evacuated it, let it sit overnight and saw no leakage.
Started adding r134a without the engine running, letting the vacuum draw some in, and then started the engine.
Compressor clutch engaged immediately, and using a refrigerant chart, filled it to 45psi on the low side, and 170psi on the high side. Ambient temp was 75F.
Thermometer in the side vent read 52F.
Really happy with the result!

Now, to the controls: There is no airflow from the "face" vent, no matter what we do with the controls.
Looking at the service data provided by Motorcarman, it could be a number of things...hard to know where to start.
At least the A/C works well enough to take it to local car shows on hot days. This is Chevy/Ford/Mopar country, and this XJ40 gets a fair amount of attention because it's "different".

Thanks for all the help. We added a new tool to the toolbox that paid for itself already.
I saw another thread that dug into the control side, and I'll keep this thread updated as I puzzle this out.

 

Ok, well first thing to check is whether or not the cold air is being "sent" to the centre vent - (if that is what you mean by "face vent" -if no air from side vents too, different ball o'wax)

This test takes for granted that both of your blowers are running.

To check, pry off the wood trim at centre vent and remove the plastic grille/vent. If you peer in there with a flashlight with controls set at max cold and car fully warm you should see the vacuum flap open. If it's closed, get something like a chopstick and push it open. With it open you should get a blast of cold air. You can wedge it open to get face vent air temporarily til you figure out why it isn't operating with vacuum.

If the vacuum flap IS open and you don't get a blast of cold air, then something is preventing the upper blend door in the climate control unit (CC) from operating. That can be a couple of things, the main reasons are a broken demist flap falling down from the upper part of the dash into the heater and jamming the mechanism (common), a faulty motor on the side of the CC or a faulty/bad connection at the climate computer. The motors and the computer are mounted on the RH passenger side of the unit.

 

Vacuum plastic pipes have a color to the different actuators.
BLUE = recirc.
RED = heater valve
GREEN = demist
BLACK = face vent

Vacuum diagram for info from my student guide.