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POA virsus STV

67vetteal on Tue January 17, 2006 11:11 PM User is offlineView users profile

Year: 1967
Make: Chevrolet
Model: Corvette
Engine Size: 327
Refrigerant Type: R-12
Country of Origin: United States

Years past I installed a "Factory" correct A/C system from a donor car. I did a complete system install including dash ducts and switches. My car is a 67 and the donor car was a year or so older. Therefore it used an STV virsus the 67 having a POA. Seeing as I have the engine out I am in the process of correcting this situation. I have two POA valves (used) and need to check them. How can a DIY guy accomplish this? Will I run into any Problems by doing this conversion? Thanks, Al W.

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

TRB on Wed January 18, 2006 11:12 AM User is offlineView users profile

Use the Google search on this fourm and you wiil find a lot of information on POA testing. Our old Friend Mitch and Dougflas did a lot of work concerning POa's a few years back. Here is just one thread on this topic,


When considering your next auto A/C purchase, please consider the site that supports you:

Dougflas on Wed January 18, 2006 9:20 PM User is offline

I have a tester that will allow you to use shop air and a set of guages to test and set a POA. If I can find the photo of it, I'll post it. If not, give me a day to photograph it and then I'll post it. It is relatively easy to do.


robtemple on Wed January 18, 2006 9:51 PM User is offlineView users profile

Although I haven't dealt with suction pressure regulated systems in ten or fifteen years, I don't remember much difference (if any) in POA vs. STV valves. They both were virtually the same size. And they both maintained 28-32 PSI, keeping the evaporator in an R12 system from freezing up. Other similar systems were VIR, EEVIR, and EPR.

POA=Pilot Operated Absolute valve
STV=Suction Throttling Valve
VIR=Valves In Receiver
EEVIR=Evaporator Equalized Valves In Receiver

Rob Temple
Ford/Acura/Hyundai Tech

Dougflas on Wed January 18, 2006 11:48 PM User is offline

If this will help, the test set up is: You'll need to get a fitting to fit the input (evap) side of the poa. You can either weld a hose connection for your gages onto this fitting or use hose clamps and a bushing from a plumbing store. Then take your manifold and connect the high side hose to shop air ( 70lbs) You need at least 60 lbs. Connect the yellow hose to the fitting you just made. The low side hose goes to the fitting at the side of the POA. (make sure you zero the low side gage). Close both handwheels. Open the high side handwheel slowly and listen to the POA for a pop. Then increase the highside handwheel until fully open. The low side should read 30. (28 to 32 depending upon your sea level). This is for R12. If using R134a, you'll need to recalibrate the POA. At the input side you'll see a 5/16 inch nut with a screw thread in it. Loosen the nut, with pliers turn the screw counterclockwise 1/4 turn, and while holding the screw, tighten the lock nut. It is tricky and is trial and error. Retest. You're looking for approx 26lbs on the low side gage.

67vetteal on Thu January 19, 2006 8:55 PM User is offlineView users profile

Thanks Doug, I'm on it and will reply in a day or two. Al W. Rob, Thank you also. I need all the help I can get! lol

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

cisgww on Mon May 24, 2010 2:50 PM User is offlineView users profile

Dougflas-hope you see this post, couldn't figure out how to contact you directly/personally.

Found your Automotive Air Conditioning Procedures, Tips and FAQ on testing a POA.

I have a 72 442 with Type 1 POA that needs testing. It is removed from the car. I have no manifold like you, but can make the adapters and have other gauges needed. After more reading, and (I think) a better understanding....can you/someone confirm:

With an adapter, I supply regulated shop air of 60-100 psi to the (lowside) big inlet coming from the evaporator?
To see the psi setting of the POA, I fit a gauge to the (highside?) port going the TXV (expansion valve)?
I cap off the oil bleed line?
I do nothing with the "Shrader" valve near the input end of the POA through which refrigerant is added?

Is the POA adjuster screw/nut now under my adapter, the end coming in from the evaporator?

At is a pic of a test setup by Mitch which shows a socket sticking in the other end of the POA which goes back to the compressor. I assume in the style POA shown, the adjuster is in the output end?

If you email me, I can send a pic of my setup...which I think is wrong after my first attempt at understanding your procedure.

Mechnicaly inclined, but A/C challenged!
email: cisgww "at"

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