This vehicle sat for 10 years but is back running now. The A/C doesn't cool, but there is 12 PSI on the low side, so I'm hoping all I need is some R134. The compressor clutch won't kick in and that is most likely do to the low pressure. I think there is a protective switch..I tried jumpering the relay but that did nothing. So now what are my options? How do I charge the system enough to get the compressor clutch to activate? According to the person that owned the car prior, the A/C was working when it went into storage 10 years ago

 

Just for the heck of it, check the fuse first. It’s definitely low on refrigerant and not enough to kick it on. When it’s time to charge the system, it *should* be enough to kick it on. If it doesn’t, you’ll need to find the compressor clutch relay, pull it out and make a fat wire jump from 30 to 87a. Of the 4 prongs that are in the relay socket, the one odd ball facing slot and the one directly across from it are the 2 you want to join with a wire and the compressor should be running.

 

12 psi means almost completely empty. The system needs to have at least some 30 psi (controlled by the pressure switch on the condenser) for the compressor to be activated. This is easily achieved when the gas cylinder is connected to the system and the charging valve opened. After some pre-charge with the engine stationary, the engine is started and the charge completed with the engine running.

 

In my non-Jaguar, non-professional experience, auto HVAC systems are sealed and fully closed loop. If the refrigerant pressure is low its because you have a leak somewhere in the system. You can refill it or top it off and I bet the compressor will kick right on when you do, but it'll eventually leak right back out and you'll be without ac again. It might take years for it to leak out or it might be hours. If you refill it, use refrigerant with dye so you can check the system for leaks with a UV light. I've had some success with DIY aircon repair, but not 100%.

Just my 2 cents.

 

Take a look at the pressure valve (just back of the radiator on the left side): if you see green, it is leading. Easy replacement and lots of Youtubes on reloading the refrigerant (one actually shows an XJ8), just don't overfill.

 

Yes, the pressure switch is easy to replace. However, the Schrader valve underneath it is very likely not going to seal when you take the switch off. The spring loaded valve is held in the open position for the better part of 20-25 years (depending on the year of the vehicle) and will not be very successful sealing in the refrigerant once the switch comes off. I just wanted to throw out that word of warning because I know from experience replacing those valves usually ends up not good with a system full of refrigerant and a hit or miss with that valve under it. Just saying.

 

There are many places in the A/C system that leaks can occur, however with these highly engineered
cars, Jhartz and Addicted2boost are correct that the pressure valve is a likely spot. I like mayhem’s
suggestion of using a refrigerant with dye, because it may be leaking from more than one point.

 

You should see green from where it is leaking. I had no leakage when I switched out the pressure switch: but I did overfill it, blowing the new switch too. Bled off some of the refrigerant when installing the third switch (it is an illegal act in some states!), worked fine for next couple of years. . .