POA Valve Honking/Pulsing

[major_mitt]

Hi everyone,

My name is Matt, I live in New Zealand and have a 67 Buick Rivera that I've owned for about 13years.

I'm going through the A/C system in my Riv (has never worked in the 13 years I've owned it).

I was bench testing and trying to set the POA Valve for R134a by blowing ~100psi shop air through the evaporator. Instead of smoothly regulating to the 30PSI expected, the valve opens and closes repeatedly and the low side pressure fluctuates between about 25 and 27PSI. There is a loud honking sound that accompanies the valve opening and closing.

I took a video of this happening. You can watch it here:

https://youtu.be/RDyZSpX0VFs

[JohnHere]

Welcome, Matt. For R-134a, I believe the POA needs to be calibrated to 26 PSI to work properly. Search this Forum for the specific procedure, which has already been discussed and pictured in detail.

[major_mitt]

Hi John

Thanks for your reply.

I was trying to follow the guides I’ve read here and tune it down for 26psi.

I’m just not sure if the fluctuating gauge reading while blowing air through the valve is indicative of a faulty POA

Cheers

[Dougflas]

1/4 turn counter clockwise from R12. POA should not pulsate. your looks bad.

[JohnHere]

Matt, your POA valve could be defective as mentioned. But before presuming that it is, I would test it again using reduced air pressure of around 60 to 80 PSI. The pressure you used, approximately 100 PSI, seems too high to me when you consider the pressures at which the low side typically operates. The high test pressure might be causing the fluctuation/honking that you're seeing.

[major_mitt]

Thanks for the suggestions.

An update for posterity:

• The valve had initially tested OK when I first pulled the evaporator out.

• It started honking after I cleaned the mineral oil out with A/C Flush solvent.

• I added a couple of drops of PAG 150 oil to the inlet of the valve and re-tested.

• The valve stopped opening and closing and regulated properly at my new set pressure of 25psi and was quiet.

• It started to get a little bit noisy after some of the oil had blown out.

I guess with the system in proper operation there should be adequate lubricant flow. Whatever mechanism that is in the valve must require adequate lubrication to function correctly.

I'm going to attempt to run the valve as-is.

[tbirdtbird]

FWIW I do not know what kind of magic is in commercial flush you buy at the auto parts store.
We use naptha here. It dries quickly and leaves absolutely no residue.

As far as adjusting the valve for 134, I would heed the suggestions of Dougflas and JohnHere if you want it to work correctly with 134. These guys are some of the best of the best

[JohnHere]

When testing a POA with compressed air, you should hear a "pop" when the valve reaches its set-point and then a "hiss" as the air flows through it. The noise and pressure fluctuations that you're seeing appear to be abnormal. Could this behavior be caused by the old internal soft parts and exacerbated by solvent-flushing? Maybe. But as you mentioned, the problems might disappear once it's re-installed. If not, there are several shops in the USA that can rebuild, calibrate, and test your POA to like-new condition as long as it was made by Frigidaire. Delco-branded units can't be rebuilt. I don't know about any shops that offer a rebuilding service in New Zealand, though.