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Pressure relief valve blew open!

Engineer on Sat July 16, 2005 6:22 AM User is offlineView users profile

Year: 1990
Make: Honda
Model: Civic (DX sedan)
Engine Size: 1.5 L
Refrigerant Type: R-134a
Ambient Temp: 85 deg F
Pressure Low: ?
Pressure High: ?
Country of Origin: United States

Greetings, I am a newbie to mobile A/C work, and to this forum.

I have MANY years of experience in auto repair but very little in auto A/C repair.

Last Thursday night (7/14/05) I was sitting in my car in a parking lot with A/C running. I had the engine idling at a fast idle when the pressure relief valve on the A/C compressor blew open and released all the refrigerant to the atmosphere! There was a VERY LOUD hissing sound! I was kind of BLOWN AWAY by this event! :-)

A little history on this car:
May 2004 - the A/C was not working. I determined that the compressor clutch was defective. I then replaced the compressor with a reman unit and converted the system from R-12 to R-134a. Since I didn’t have the required (EXPENSIVE) A/C equipment, I had a local A/C shop reclaim the R-12 from the system. (They were happy to do this for free!) I then replaced the compressor, receiver-dryer, put in ester oil and installed the R-134a service ports. The Schrader valve core on the low side was broken and fell into the metal tube leading to the evaporator when I tried to remove it. (This made me a little paranoid). I then added R-134a to the system, fired it up and it seemed to work fine for the next 14 months.

7/14/05: Pressure relief valve blows open and releases all the refrigerant to the atmosphere.

7/15/05: I removed the (reman) compressor and the pressure relief valve. A LOT OF OIL was also blown out from the compressor, along with the refrigerant. I was forced to go to my local Honda dealer because nobody else had the valve available separately. I am now waiting for the special order to arrive.

Once I receive and install the new valve, I plan to have my local A/C shop evacuate and recharge the system with oil and refrigerant. I also plan to make sure the condenser fan is working properly.

My current problem: I don’t know WHY the relief valve blew open (I am still paranoid about the lost Schrader valve core). Once I get the system working again, I want to prevent future failures.

I also plan to buy some manifold gages ASAP.

Can you give me some advice; tell me what to look for at this point?

Thanks in advance!


To thine own self be true.

Chick on Sat July 16, 2005 6:43 AM User is offlineView users profile

Well, when you changed the compressor, you had a shop recover the R12..They should have told you to bring the car back for a vac/recharge. But you added the R134a without pulling a vacuum, and I really am surprised it lasted 14 month. You had to have air in the system, and air is not condensable. So the high side will build up pressure and eventually, blow the relief valve. You can do this whole job yourself, guages are the first sep. Check out DIY'er starter kit which will have the guages, vacuum pump and can tap. Then you follow these Vac/charge procedures, make sure the condenser fans are operating properly and you'll have nice cold Ac again, and the tools to fix family and friends AC systems. The tools will pay for themselves, not conting the satisfaction of doing "all" your repairs now.. But if you don't want to fool with Ac systems, then have the shop pull the vacuum and recharge the system..Hope this helps.

Email: Chick


Freedoms just another word for nothing left to lose

bohica2xo on Sat July 16, 2005 5:57 PM User is offline

134a conversions are all "custom" systems when you charge them. You need both high side & low side pressures, and some care when charging them.

Hondas have little or no reserve in the condensor, and converting them in hot climates can be tricky. Many honda models spec a complete new system for conversion in the factory manual.

We test systems with the doors open, fan on high, and the engine speed at 1500 to 2500 rpm for a reason. The worst possible case. If you charge & test at idle, the pressures can be MUCH higher at higher engine speeds with no ground speed - as you just proved with the relief valve.

You will want to be careful adding the final charge to this vehicle. Monitor the high pressure, and stop if you see more than 350 psi on the high side. You can road test the vehicle with the hood closed and check the pressures at actual operating conditions. A recent poster had sucess doing this with his honda, try a search.

As for the missing valve core - since the system is apart, flush and clean the suction line it dropped into at least. The best thing to do is flush the entire system, so you know exactly how much oil to add. Too little oil, and you kill the compressor - too much oil, and you lose cooling capacity....


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Shehzada on Wed July 20, 2005 3:39 AM User is offline

When refrigerant has been evacuated and then thoroughly vacuumed, should then a flush be done? Does flushing remove all of the compressor oil in addition to the contaminants?

k5guy on Wed July 20, 2005 3:52 AM User is offline

Yes, you can flush once you've reclaimed the refrigerant. After the flush, you need to draw a good vacuum after you reassemble everything. The flush will remove any old oil, so you'll have to replace the oil with new.


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jwcrawford on Tue September 02, 2014 7:04 PM User is offline

Concerning pressure relief valve. My compressor on my 2000 Chrysler T&C locked up so I installed a used compressor and pulled vacuum on the dual system. Recharged system and the valve released at 150psi. I manually activated both condenser fan and cooling fan and recharged again. The valve release at lower psi. I put a new valve in and vacuumed and recharged and was able to get pressures to 200psi before it release again. After the final recharge I was able to get the rear to cool some, 82degrees. It never would cool properly. No sure what is going on. Not sure why it locked upped. Anyone have any ideas.


mk378 on Tue September 02, 2014 8:03 PM User is offline

Your condenser is probably clogged up with compressor debris. I assume the high side port is after the condenser, so the pressure at the compressor could be much higher that what you see at the port.

Jag987 on Fri September 05, 2014 10:29 PM User is offline

Anyone notice this thread was 9 years old?

I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

Edited: Fri September 05, 2014 at 10:30 PM by Jag987

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