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A/C High Pressure Valve

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RoryBarron

10+ Year Contributor
313
4
Jul 19, 2009
Oklahoma City, Oklahoma
Hey guys (and girls), I have a problem with my air conditioner. I haven't ever had it work consistently. Since I bought the car I haven't drove it for more than 2 months at a time. When I got it there was no a/c on it at all. Since then I have put new: compressor, drier, condenser, and thermal expansion valve. I put used lines and a used evaporator core on. (off a car that had working a/c when wrecked). The lines are not clogged. I have searched and found one other thread that is similar. This one.

So the problem is very similar to the one in the thread. My a/c seems to work fine unless I let the car idle then try to get in and drive it. Following that the pressure relief valve pops and drains the freon. It has done this twice, the first time I replaced everything (hence the new parts). The replacement compressor did not come with a new relief valve, only a plate bolted to the top. I had to swap mine over from the old one. I have looked for a new valve since the cover is gone from mine as well.
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Like this picture.

One other thing to note is that I can hear the expansion valve relieve pressure moderately loudly. Not ear splitting but I can hear it over my engine when getting to highway speeds.

I also had a friend from mitsubishi charge the a/c after I replaced everything. This includes vacuuming it, adding the oil charge, and the freon. I trust that the charge itself is not the issue, though it is possible something in the a/c system may be blocked.

So is it likely my problem lies with the expansion valve, evaporator, or the black box of death described here? I am going to replace that box this weekend from a parts car. (Also a 95 Gs-t) Rep points to the person who actually helps me with this! :hellyeah:
 
Well i dont think the cover is really important its just to keep dirt out and is only stuck on. As for your issue. Your a/c ecu must be good if your compressor is engaging, as its sending all 12v to the clutch wire. I would try to get another pressure valve. And get it recharged and make sure the pressure is correct.
 
^^^what?

Sounds more like the high pressure valves stem is leaking and it may have either A launched the cap off of B never had a cap.

good way to check is to go ahead and get some uv dye in a can and run it through the a/c system and use a black light and search out any green coming out.
 
Everything has been replaced, I may just replace the cap to be on the safe side. As of today it looks like I won't even need the a/c again this year. If it still does it I will end up replaced the evap core and expansion valve with another new one. No point in only replacing one when I pull it all apart.

If the pressure relief valve isn't the culprit then what is suggested that I look into next?
 
Well I have two compressors in front of me and both are missing the cap, one just fell off as I removed it from the car. I dont really see what it does other than keep dirt out.

Well that sir you are correct all they do is keep dust and grime from getting in and making the shraider valve stick. Otherwise its pointless. The shraider valve id recommened replacing since you can get a set of them for like 5 bucks at autozone. and get a stem removal tool for it.

chances are thats what is needed.
 
Well that sir you are correct all they do is keep dust and grime from getting in and making the shraider valve stick. Otherwise its pointless. The shraider valve id recommened replacing since you can get a set of them for like 5 bucks at autozone. and get a stem removal tool for it.

chances are thats what is needed.

Did you even look at the picture? :rolleyes: We are not talking about the schrader valves. I am talking about the high pressure relief valve. Both schrader valves were replaced as I did not feel comfortable using valves that are 15 years old (stock). Neither leak. I know those are not the issue.
 
Pressure relief valve ended up being the culprit, assumed. I replaced it, recharged it and since then it has been just fine. Thanks for the help guys.

My pressure relief valve is bad. I vacuumed out my system, it held the vacuum, but as I was filling it I heard a hiss. It leaked out from that valve. My question is where do you buy this valve. They don't even have it listed on mitsubishiparts.com. Do you have to get it from the dealer? Where did you get it and how much was it?

Thanks,
JJ

Okay, I was able to find the part. Part number MR360020

and it's about $18 shipped here in case anyone else needs one.
 
My pressure relief valve is bad. I vacuumed out my system, it held the vacuum, but as I was filling it I heard a hiss. It leaked out from that valve. My question is where do you buy this valve. They don't even have it listed on mitsubishiparts.com. Do you have to get it from the dealer? Where did you get it and how much was it?

Thanks,
JJ

Okay, I was able to find the part. Part number MR360020

and it's about $18 shipped here in case anyone else needs one.

I got mine from an automotive air conditioning store.
 
I got mine from an automotive air conditioning store.

When you replaced yours, did you take the top cover off, drain the oil and refill? Supposedly you're supposed to do this. If you did, what did you torque the bolts to? I can't seem to get this information anywhere. I've tightened them to 14 ft/lbs, because I'm afraid to ever-tighten them and strip the aluminum housing. After pressurizing, i noticed a small leak with my sniffer so I know they need to be tighter.
 
Hy have a question about my a/c almost going trough the same thing its for a 99 Windstar was working fine and all of the sudden it started relicing my freon and suddenly it stop that was the first time and almost getting home all of the freon was relise any sugestion whats the problem or its just the relive valve that it gave up or what can it bee wrong. Hoe to here from someone that can help me out with that ill appreciate it thank u.
 
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