I have a 96 XJS with the 4.0.

I had an issue (warm air) with the AC recently which I was convinced was due to an obvious leak in the high pressure hose. I fixed the hose with new crimps and a newly brazed test port, and blew compressed air through it to make sure there were no obstructions.

Tied everything back together, ran a vacuum for a long time. Closed off the high side and started adding refrigerant to the low side port. Everything was going ok for a little whole, I just can’t get the high side to get above 125psi! It’s coming on, but it wants to be at 100psi, and occasionally gets up to 125…maybe, but that’s it.
Low side is charging up, gets to 70psi, but compressor oddly enough doesn’t want to compress higher than 125. Air is still warm to hot at the vents. I have it set to manual, on highest speed, and AC button is on.
What should I check?
Reply

 

I'd replace the expansion valve first. At 16$ plus shipping it's a good place to start.

Next I would do a static test of the compressor. You should feel suction on the inlet side when turning by hand and it should quickly build up pressure on the outlet side.

The low side at 70psi is telling. You have an obstruction, bad TXV or very week compressor.

When running partially filled you should get a vacuum on the low side until the high side builds to 140psi or so. You should have 20 to 40 psi on the low side and about 220 on the high side

 

Yep, expansion valves, compressors, driers, evap cores common on this model to fail.


+1 icsamerica on operating pressures

 

Thank you so much. I went back out there and tried one more time after letting it rest for an hour or so.

I don't know what I did, or didn't do before, but the system drank a 35oz bottle in seconds. I added a bit more to get the high side to kick off at 160psi, which for a 72F night, seems to be well within range. Air temp at the center was registering 47F.

I think I'm good. I wish I knew what I did wrong.

 

Your TXV valve was probable hung up, the heat cycle freed it up. Quite common and a sign your TXV is suspect.

Also did you add oil to the system some how? Raw R134A will has no lubricity. With an opened up system you should have added at least 4 Oz. Some a/c recharge cans already include the oil...some don't.

 

I did replace the TXV when I bought the car a few years back. The condenser was bad, so I replaced the condenser, drier and TXV. It's something to keep an eye on though. Thanks for the tip.

I did not add any PAG oil. (This thing takes PAG100, btw). I now realize I should have added some oil. It's not too late!

The manual does indicate how much oil you can estimate as you replace each piece. It estimates what 30-40ml be replaced with a refrigerant change. The total capacity stated in the manual is 120-150ml, about 4-5 ounces.

The AJ16 side of the manual estimates 80ml for the compressor, 30ml in the oil separator.

The AJ6 side of the manual estimates 1 ounce for a drier, 3 ounces for a condenser, and 3 ounces for an evaporator.