Broken POA Valve?
 

I've been reassembling my A/C evaporator, expansion valve and POA and figured I'd adjust the POA for 134a. I wanted to get a bearing on where it was set at first so I set it up to test.

I hooked up the low side gauge to the POA and ran compressed air through the expansion valve into the condenser to build up pressure. I was expecting it to build up to 30" or so, but instead I almost immediately heard a big pop from the POA valve. Now it won't hold any pressure and blows right through (showing 12-15" on the gauge).

The system worked reasonably well before I took it apart. I'm assuming that the POA is toast now? Is there any way to repair it?

If I need to replace it, has anyone used one of these OEM-looking POA eliminator kits that make the compressor cycle?

https://www.originalair.com/15-52-ac...iminator-valve

Can you perform a more detailed measurement of inlet pressure vs low side pressure. using your gauges? There should be a "knee" at the point the POA begins regulating. If your "knee" is there but at a different pressure,a flush without the adjustment screw in place may dislodge and exit the POA. Reattach the adjustment screw and set the pressure for the refrigerant you're going to use..

I've attached some bench test and in-situ plots of a good and a bad POA to give you an idea what to expect.

I have been successful unfreezing a stuck open POA valve and attached a before/after pressure reading as well. I made my own attachment from plastic electrical couplings and brass fittings. You can buy them too but they are a little pricey.

I'd recommend a TXV bench test over temperature.on the expansion valve. If you need some guidance on how to proceed, let me know.

As of right now, it doesn’t look like the “knee” is there. I’m seeing about 12” at the valve with the air blowing right through so maybe it’s stuck. Thanks for the info - I’ll try flushing it and a bench test to see if I can get it working.

Can you elaborate on what fittings you used to make the attachment? I went to the hardware store today and couldn’t find a combo of fittings that would work. In particular, the thread of the a/c hose fitting seems to be unique.

The 3/4" plastic electrical conduit and it elbow was bought at Home Depot. The 1/4" flare brass fitting and adapter was bought at Lowes. Parts numbers may be found in the photos. The 3/4" conduit thread is not exact but will engage and deform the threads without damage to the POA. The pressure seal is maintained by a rubber O-ring I got from a set bought at Harbor Freight. If you look at the threads side by side to an actual adapter, you can see they are very close.

Appreciate the details. Unfortunately, I wasn't able to get anywhere with the original POA so I broke down an ordered the billet POA-eliminator from Old Air. Not quite exact in appearance, but it's in the ballpark. They have you add an additional thermostat to cycle the compressor and splice the wiring into the stock harness. I mounted it down low on the evaporator case so it's not as noticeable. We'll see how this thing works.


https://forums.maxperformanceinc.com...1&d=1656790183

https://forums.maxperformanceinc.com...1&d=1656790151

https://forums.maxperformanceinc.com...1&d=1656790188

Verdoro 68, what are your thoughts so far using the billet POA eliminator? I’m at the point of ordering either a recalibrated POA or the eliminator for my 67 GTO and 69 Caprice….

My thoughts are that if you are retaining a factory type of A6 compressor, go with a re-done original POA. From what I've read and heard, the A6 wasn't designed to be cycled and wont perform well if you do.

If you go with an aftermarket like a Sanden or one of the aluminum A6 drop-in replacements like the Pro6Ten , then going with a POA eliminator should work fine.

Just an FYI...I have the Pro 6 Ten in my 67 GTO and that POA eliminator does not work. I bought a refurbed original.

Thanks for the input….looks like I’ll be purchasing two recalibrated OEM POA valves tomorrow

Hello,
I just came across this thread while researching some AC issues I'm having on my '70 GTO. I don't know if I go w/R134 or stick w/ R12.

My question is that if POA valves aren't being made any more, where did/were you getting an R134 recalibrated unit from? Any information would be appreciated.

Thanks,
Larry

It's not difficult to readjust the POA using a set of gauges on a bench or even while in the car. The is a hex screw and jam nut that is ilocated in the output side. After loosening the jam nut, rotate the hex screw and retighten the jam nut. Test for the new pressure. Repeat if you're unsatisfied with the results.

If you wish to send it out for recalibration, a place like Old Air Products or Original Air Group can perform the work. Specify you don't want a restoration, just a recalibration.

Awesome! Thanks for the information and illustrations. But for R134, what should the pressure be adjusted to?

The 1967 Pontiac Service Manual states that the POA operated at 28.5 psig for R12, This corresponds to 30°F. From the R134a pressure temperature curves, a 30°F temp corresponds to a 26.1 psig. This is the nominal setting to strive for.

That completes the picture - thanks again.