94 XJS 4.0 no AC

Last year my AC needed a top off of 134A to get it working properly. This spring it appears it no longer works. The symptoms are: Only heat coming out the vents, AC compressor clutch is not kicking in and there is not much air blowing thru the center vents. Tried to top it up but even with the AC clutch jumped it not working. My Low pressure and high pressure lines are easy to see but I cannot seem to locate the pressure switch. Its nearly impossible to see or get to anything inside the car even with knee bolsters and console panels removed.
Any ideas where to begin?

Sounds like the normal for a '94 :roll_eyes: … Superblue’s a.c. has always been that way ever since I owned her … :frowning_face: Come to think of it, I never had a Jag with WORKING a.c. :angry: I guess things don’t get very hot in the U.K.? :confused: You quickly learn to just drive with the windows down (and sunroof open, if your cat has one) in the summer, park in the shade (or put one of those covers over your windshield whenever you can’t) … :smiley_cat:

The pressure switch for the 1996 MY with the AJ16 engine was near the passengers head lights in the engine bay. Just follow the refrigerant tubing until you find a sensor plugged into it.

If that clutch isn’t kicking in, even when jumped, wouldn’t that indicate a dead compressor?

Lack of air at the vents could also indicate a leak at the evaporator coils, which would cause the coils to freeze up and block air. Is there air blowing through there any differently when you haven’t tried to run the AC for awhile? If it’s blocked up all the same, then it would be unrelated.

In any case, I would find that pressure switch, test it, and then think about replacing the compressor. To do this yourself, you’d need a vacuum pump, R134a manifold (harbor freight sells a good one at a good price) and some refrigerant. You do have a leak somewhere, so some AC dye would be a good idea. Assuming your leak is not behind the dash, everything should be pretty straightforward to work on. Your leak might just be at the easy to replace schrader valves.

…or you can just find a shop to take it to. There’s nothing exotic or fancy about the AC system in these cars. Lack of a working AC system is a deal breaker for me.

My 95 v12 a/c works quite well. Provided it is charged and doesn’t have a leak :-). I live in south Alabama and my car is black, so on hot and humid days it takes a bit of time (about 8 minutes) to get the cabin temp comfortable.

During my 19 years of owning this car i have had to replace the compressor once, and replace the back end after a crack developed. and another time replace a schrader valve that leaked out the 134 refrigerant.

If you don’t have enough pressure the low pressure switch will not let compressor run.

I agree with letting a good A/C shop work on it.

Found the pressure switch, thanks VeeKay. I will test it later. Is the pressure switch something I can easily obtain? The air is blowing thru all the vents, just very weak thru the central vents only. It leads me to believe a “door” is not opening all the way. MY94 has a vacuum valve pack according to the climate control documents I have. Unfortunately they don’t give me any idea where it is. I though I might access that to test the operation of the doors that blend the air.

Maybe this can help

(Attachment ac-delanair-mk-iv-air-conditioning-system.pdf is missing)

Jim D, I may have this but the attachment did not make it.

Charles, turned out it was too large for JL. You can email me at jim.d@roadrunner.com and i can send it to you direct. It is a Delainer Mark IV training manual in pdf file. Perhaps you already have it…i also have this smaller file of earlier system.
aircon-schematics-mk3.pdf (285.9 KB)

A long time ago I pulled the center console out and I diconnected the rear vent (not sure you have one) and blanked it off using a rubber cap. That increased the air being pushed out into the front vents, so I don’t remember what the air pressure at those front vents should be anymore.

That pressure switch is not a common failure point. The part number for my system is DBC11279, and is still available new, although I would not want to pay that price. I don’t exactly recall, but I believe if you jump the two contacts on the sensor (with the car on and the AC on), you should hear an audible click. Whether your compressor does anything with that click is another story.

Im going to do that. I have already removed the rear seat and in the process of fabrication a custom cubby box.

Thanks JimD. My email is ctw4155@gmail.com

Now you got me curious … (1) why (does DC get that hot?) and (2) how many Jags have you bought (old) that had working A.C. in them, VK? :confused:

I agree that the V-12 a.c. (6.0s) system is probably a better and easier set up to work on than with our 4.0s, assuming it still has the compressor right up on top like the 5.3s. One thing I noticed when I tried to work on Superblue’s a.c. myself right after I got her, mostly using one of those “recharge + leak detector/sealant kits”, was that if you turn on the a.c. the engine temp starts going up quickly, soon into the red. :open_mouth: To me, that sounds like nothing to mess with, so I just let it be after that point (and after the recharge bottle suddenly took off into the air like a skyrocket while I was attempting to put refrigerant in her system - good thing I didn’t have my face over it at the time). :grimacing:

Actually, someone posted earlier something about that which surprised me - the facelifts went to electric solenoid motor systems to activate the HVAC flaps, vs. vacuum operation on the pre-facelifts. ?

Wouldn’t just closing the vents (using the little lever) do the same thing, or does a lot of air flow still escape out? :confused:

  1. Damn straight DC gets hot….and humid! City was built on a swamp. We spend a lot of the summertime In the 90s. That’s too hot.

  2. Im two for two with Jaguars with functioning AC. If the AC isn’t working, Im either not buying the car, or spending whatever it takes to fix it.

1 Like

I would never use a can with sealant for any cars AC system. Either fix it outright, or get rid of the car. Sealant will only complicate things down the road.


The rear vents in the 96 have no lever or way to adjust the air flow. Even if it did, I’d probably do the same thing since no one ever sits in the back and, quite frankly, even if they did, the compact cabin means conditioned air gets everywhere rather quickly.

If you are going to diagnose your defective A/C system I would suggest that a pair of gauges should be your first option. They are relatively inexpensive and will immediately tell you what your high and low pressures are. That’s where I would start.

Again, the manifolds (or gauges) at Harbor Freight (if you have one nearby) is worth the cost of admission. It will allow you to diagnose and vacuum out and recharge your AC system.