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POA Valve Problem?

rgriff on Sun June 04, 2006 8:39 AM User is offline

Year: 1971
Make: Chevrolet
Model: El Camino
Engine Size: 350
Refrigerant Type: 134
Ambient Temp: 86
Pressure Low: 32
Pressure High: 160
Country of Origin: United States

Did a frame-off on my '71 El Camino. The A/C system was removed and stored with all openings taped off. It was re-installed with new compressor and dryer, then evacuated and recharged. It had already been professionally converted to 134 by the PO. It cooled great for about 2000 miles (several months) with no problems, then suddenly began blowing hot. I took the unit to a shop that does not do A/C repairs and they put more 134 in. It still blew hot but according to the technician the pressures were very high. He unhooked the compressor and suggested I take to an A/C shop.

My regular mechanic checked it and he suspected an expansion valve, although he said he was not familiar with POA valves and it could also be that. I looked up the info on testing the POA valve at and took the truck to him along with this info:

He replaced the expansion valve. and using the method described on the A/C forum, he tested the POA. The original POA would not read anything on the gauges. I got a used POA from a local wrecking yard and he tested and adjusted it to 26 lbs. He was unsure that it was set right, saying that there was another line going into the evaporator that was not plugged and he did not see how you could get a correct reading. After charging with what he felt was the correct amount of 134 the unit still didn't cool and the pressures were low. He continued to add 134 until the pressures were acceptable to him (30 to 35/150 to 175) and the air coming through the vents was only slightly cool, nowhere near what it needed to be to cool the vehicle. HE also showed me that the lines were frozen up to and including the POA valve, but barely cool if at all beyond that.

Any suggestions as to what to try from here. My technician wants to eliminate the POA valve and retrofit a pressure cycling switch somehow. I would rather get it repaired as it is.

P.S. Sorry this is so long. Thanks,

Ron Griffith

JJM on Sun June 04, 2006 1:02 PM User is offline

Keep charging... but before I go on, I have a number of problems with the people you seem to be dealing with.

First, your "technician" admits "he was not familiar with POA valves" so how can think that's the problem if he's not familiar with them??? If he's not familiar with POA valves, then he shouldn't be working on the vehicle, period! Why should you pay for guess work! And his solution: "My technician wants to eliminate the POA valve and retrofit a pressure cycling switch somehow." Stupid! Like have the compressor clack on and off is somehow better.

So if you bought a brand new car with a navigation system and your tech didn't know anything about it, would you accept a compass mounted on your dash instead and stare at a blank screen? I didn't think so.

On POA and STV systems, if the suction line leading from the POA to compressor is frosting up, and the system is not cooling properly, this is a classic indication of an undercharged system! But to make matters worse, it looks like he adjusted the POA the wrong way, because an undercharged system would cause the POA to activate and hold the lowest pressure it's set for. If it was set for 26 PSI, it should hold 26 PSI, but yours is reading 32 PSI.

How this "technician" could've "felt" he charged the system with the "correct amount of R-134a" with such low high side pressures and a frosted suction line on POA/STV system is beyond me.

One quick test, if the low side pressure is less than whatever it is set for – even with the blower motor wire disconnected – the POA valve is defective and should be replaced.

The high pressure looks awfully low for the ambient temperature and a stock tube and fin condenser. Were those readings taken at idle or 1,500-2,000 RPM. Even with R-12 they would be low.

By the way, the new expansion valve, is it externally equalized, in other words does have the sensing bulb clamped to the evaporator tailpipe, and the other line connected to the POA? Are any of the ports on the POA capped off?


Dougflas on Sun June 04, 2006 1:44 PM User is offline


If you need your POA to be set correctly, you can send it to me and I'll do it for $20.. including return shipping.

ice-n-tropics on Mon June 05, 2006 10:17 AM User is offline

Hi Joe,
Sometime you should tell us how you really, really think about service charges for guess work.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Kaps on Mon June 05, 2006 11:45 PM User is offlineView users profile

You might want to have your ac service man buy this book (if he doesnt have one like it) from Tim, the website sponsor, for about $30:

Before you actually order it, you can ask Tim if it has the POA test procedure in the book. I'd be shocked it it doesn't.
Good luck with it,

A. C. Doyle said "Eliminate all other factors, and the one which remains must be the truth."

67vetteal on Tue June 06, 2006 2:54 PM User is offlineView users profile

Do a search under author, "MITCH". POA info. Al W.

Working on our 67 Vette. Converting from STV A/C to POA system as it is correct for this year car.

rallysporttom on Sun March 04, 2007 12:52 AM User is offline

I have a poa valve that I would like to get checked and calibrated if needed. Could you please email me at [email protected] and give me an address so that I can ship it to you?

Dougflas on Sun March 04, 2007 11:35 AM User is offline


you have mail

Dougflas on Sun March 04, 2007 11:41 AM User is offline

You can go to the procedures section here and read how to do it yourself if you want. You should be able to fabricate an adaptor for less than 20 bucks. If you need a fitting, check with Tim. You can still senf it to me. If you make your own adaptor, it'll be faster and you'll have the fitting for next time. Your choice.

be safe

dray8165 on Mon April 13, 2009 5:17 PM User is offline

I have a POA valve off of a 1965 Tempest I need tested and adjusted for 134a. Could you send me your contact information? Thanks. [email protected]

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