On my 1996 XJ, I have replaced the receiver/drier (it was OEM), pulled vacuum, and charged the system with R134a to a full charge. Nice and cold, great! After about 15 mins of driving, I noticed the air was not cold anymore, just barely cool. I returned home and put the gauges back on, and the pressure on the suction side was down to around 22 pounds. I checked the fittings at the drier to make sure they were tight, even though the system held vacuum for about an hour before I charged it. Yep, still tight. I topped it off, and ran it in my driveway for a few minutes. The air was nice and cold, then all of the sudden I heard a loud blowing sound. I went around to the engine and saw refrigerant blowing out of the top of the drier. Not where the pipes connect, and not at the pressure sensor, but on the "fourth" side, where nothing connects. The drier is seeming to let some of the refrigerant escape, but not all of it. It doesn't apparently leak out after the pressure goes down to around 22 pounds. What is this blank side for, and is the new drier defective? Thanks in advance...

 

A picture would really help, is there a Schrader valve in this "blank side"?

 

Besides the two lines going in/out of the drier, the other two ports are for a high/low pressure cut off switch and a hprv (high pressure release/relief valve).

Assuming you swapped over the cut off switch from your old drier and did not forget it, sounds like the HPRV might be defective. Your old one will work fine, just swap over the new o-ring. Also you might have over charged the system if this is popping. What are your high side readings?

 

I did swap the cutoff switch. The low side reading was 45 pounds, the high side was around 300 pounds. The outside air temperature was 105F.

According to the FSM, the high side can reach as high as 390 pound when the temp is over 110F, which does happen here in the AZ desert. So, this relief valve should be able to tolerate pressures higher than what I measured. Is there a schrader under this relief valve, like there is under the cutoff switch, that would facilitate replacement?

 

AFAIK the HPRV seem to reset themselves after the pressure drops down to an acceptable level.

What did you charge the system to and what are you using to charge the system?

We are looking at one of two things:

A) The system was overcharged and the HPRV did it's job and relieved some of the pressure

B) The HPRV on the new drier assembly was faulty and had a lower than normal opening pressure

 

The "acceptable level" for this HPRV seems to be 22 pounds. I used my manifold gauge set, two 12 oz. cans of R134a (with no additives) tapped and connected to the manifold gauges, and an electric vacuum pump to pull the vacuum. I added 2 oz PAG 100 to the new drier (per mfr instructions) before installation. I vac'ed the system for 1 hour, then let is sit closed up for an hour to make sure it held the vac before charging.

I charged the system to 45 pounds as read on the low side gauge. I used one 12oz can and partial of the second. Probably 2/3 of it. As it was 105F outside at the time, 45# on the low side was potentially undercharged, as the FSM states the low pressure should be 44-53# (high 270-340#) at 100F.

Based on the conversation so far, I would presume the relief valve is faulty. I no longer have the original drier to swap the valve from as it was discarded. Is this something I can find somewhere like Napa, or should I R&R the entire drier as it is under warranty?

 

It was originally 134 correct ? Def sounds like valve defective. Filling systems by out put temp is the way ive always done them with eye on pressures also just becase it say a certain pressure for a certain out side temp don't mean its carved in stone. A few pounds either way will affect cabin temp.

 

Yes, it is factory R134a, not a re-fit.

 

Ok just checking id return dryer or replace valve which evers simplest. Maybe supplier will ship ya a new valve...