Knowing this is not easy, I would still like to try if someone has some answers.

The A/C system contains an Expansion Valve and a Pressure Operated Absolute valve. Both are mentioned in the 66 and 72 manuals I have but not explained in full detail. I have three questions:

Apart from the inlet and outlet the POA valve has 3 more fittings. One is for the charging line, one is for a balance line to the expansion valve and one is for an "oil bleed line" welded on to the evaporator. In pressure testing the evaporator with 120 psi I noticed some oil coming out of this oil bleed line. Apparently there is a connection (though not completely open) between the evaporator and this oil bleed line. Does anybody know how this operates?

The fitting on the POA valve the oil bleed line connects to has a Schrader valve in it, which is not opened when connecting the line to it. This confuses me even more. How can it operate this way ?

The GM replacement for the expansion valve I ordered from Year One has a closed balance line (which connects to the POA valve), whereas the old one has an open line. Will the POA valve still be able to functon ?

Thanks

Rob

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www.si.hhs.nl/~rob (http://www.si.hhs.nl/~rob)

[This message has been edited by rusty66 (edited 06-12-2001).]

After fighting with my AC system for about 2 weeks and finally finding out that the POA was the problem. I snatched i outathere, and slapped in the POA update valve. I cut open the POA, to see how it worked, and was amazed at all the crap in it. I could not tell you how it works, or why. It is supposed to keep the pressures in the AC system constant, but thats about all I know of it.

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350 4speed 12bolt 3.73's
Bench Blue w/black inter. 14.5@90mph

Since you have not gotten any answers I will try throw in a few things. The scharder valve is just a one way valve in the line so the system does not bleed off pressure. As for the POA being blocked off. Maybe this valve does not really do much to start with. On later GM systems they only use the Expanion valves to meter the pressure.

Don

What exactly happens when a POA valve goes bad or an expansion valve goes bad? When I bought my 70 Chevelle last year there was no freon in the system and an AC shop told me the POA and expansion valve were bad. Instead, I fixed an obvious leak in a hose, filled it up and it seems to work fine. Are there any signs I need to watch for?

Blaster. The 72 manual describes a test to determine whether the expansion valve or the POA valve is stuck. I have scanned these pages and mailed them to you directly.

Thanks! Its hard to read but I got some info out of it.

Blaster. I don't know what went wrong so I put the scan on my web site for you http://www.si.hhs.nl/~rob/images/other/POA-exp-test-72.jpg (256 k). Hope this helps.

Rob


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www.si.hhs.nl/~rob (http://www.si.hhs.nl/~rob)

ChevelleCLM,

Can you provide a little more detail on the "POA update valve."?

Where did you get it? What is supposed to do? Who makes it? All that jazz. Thanks for whatever you come up with.

Tom

I am in the process of converting my 70 Chevelle factory A/C system from R12 to R134a. I purchased the core components (evaporator, condensor, dryer, compressor from my local Chevy dealer (the best price) and the Expansion valve, hose assemblies and the POA (update) valve from Old Air Products, Fort Worth, TX 817-531-2665 I worked with Jack.

The POA update valve is patented and sold by Old Air. What it does is that it allows r134a refrigerant to work with the 70's A/C system without drastic changes to the aesthetics. The r134a operates at a higher pressure than r12 and therefore without this update kit, r134a would not work very well, i.e cool not cold, constant cycling of the compressor.

The POA update valve is visably different looking than the factory syle POA but fits in the same space and allows the use of all other factory pieces, hoses, liquid line, evaporator etc. I am quite happy with the quality, though I haven't fired it up yet.

Please email me if you have any other questions.

--Andy--


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1970 Chevelle SS Convertible (being restofied)
1937 Master Business Coupe
TC #551, ACES #3513, VCCA #35642
http://home.earthlink.net/~andypap/wsnC442.html

"It's better to be thought a fool, than to open your mouth and confirm it"

Andy. In the "old" POA setup, like in my 66, the compressor is meant to run continuously. The POA will maintain sufficient cooling by regulating the pressure in the evaporator. That much I know.

I am curious if your "update" POA is meant to tell the compressor to cycle ?

Rob

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www.si.hhs.nl/~rob (http://www.si.hhs.nl/~rob)

Rob,

Yes the POA update from Old Air has an electric switch and wiring harness that connect to the compressor clutch. This will convert it to a "cycling type system" found on later model cars. On the instruction sheet that came with this valve, it specifically states that it works with GM cars 1966-1972.

email me if you need more info.

--Andy--

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1970 Chevelle SS Convertible (being restofied)
1937 Master Business Coupe
TC #551, ACES #3513, VCCA #35642
http://home.earthlink.net/~andypap/wsnC442.html

"It's better to be thought a fool, than to open your mouth and confirm it"