I have a 1994 XJS 4.0 that I'm told was actually produced in 1993, can provide VIN if helpful. It's air conditioning quit working recently so I took to my mechanic. I had noticed the compressor clutch was not engaging and wondered if it might have a low pressure safety switch as my other cars....but frankly the Jag's always seem more complex electrically and challenging to me so I look to expert experience. He said that he found an open diode, replaced it, and was concerned with possibly a relay but evacuated, converted and recharged with R134. It then cooled. He said the high pressure side was higher than he liked and had concern with the evaporator valve. We drove the car about 50 miles and the AC quit again, no compressor clutch engagement. I checked fuses, none blown. The mechanic said replacing the expansion valve will be difficult, does anyone here have experience with replacing the expansion valve or suggestions that could help. It had never totally leaked refrigerant and I won't know that situation until I can get it back to him for a check....He felt it should have a better temperature differential and that the expansion valve replacement might provide cooler air. Is there a high pressure switch that could disengage the compressor? If so, the compressor doesn't run after resting for a few hours either. It seemed strange if the compressor clutch controls are pressure sensitive or if high pressure that it could result in a relay issue. Hoping some of you have experience or a good suggestion. Gerry

 

I never had to replace the expansion valve on my 94, 4.0 but I did on my 6.0.
That is a nasty job, using a combination of crows foot wrenches and careful application of force.
My 6.0 had a pressure switch on the back of the compressor, but not sure on the 4.0.

 

Thanks, sounds like your 6.0 itself was very difficult. Looking at the challenge of replacing the evaporator with mechanic, it appears the 4.0 is maybe even more challenging than the 6.0. The "V" in the 6.0 block appears to provide a little more working room than with the 4.0. He doesn't understand what might be causing high pressures on high side but defective evaporator seems most obvious. Now, with the compressor clutch not engaging, it will require more back tracking. Any suggestions are appreciated. Gerry

 

On my 94 6.0 the expansion valve is sort of buried in the fire wall.
If you make a wrong move you can crack the copper pipe going to the interior.
Nasty work.

 

It's way easier on the 4.0. I just did this a couple of weeks ago. (The expansion valve, the high pressure valve was working fine and is not a common problem)

I don't remember which Torx sizes you'll need. Make sure you have T-25, but it could have been T-27 or T-30.

The high pressure switch is along the passenger side of the engine bay. You'll find it if you follow some hard metal pipes along that side of your engine bay.

 

I have a very limited experience with AC faults and fixes.
Did you get the car with R-134 or Freon 12?
If you or anyone made the switch without changing out all the o-rings and seals you are just chasing your tail.
R134 eats rubber o-rings, so it will leak everywhere.

 

On my 94 it wasn't a bad job. It was a factory R134a system. You need a torx socket or driver. First, remove the screw on the tip and that releases a retaining plate. Then you can pull off the two pipes going into the top of the valve. Then there are two more torx screws. Undo them, and the valve will lift right off. Replace the o-rings on reassembly.

This is what my valve looked like:

 

Gerry,

Just to let you know, it's the same expansion valve on the 4 litre as it is on the 6 litre.

Good luck

Paul