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POA revisited

ddsmith on Sat September 06, 2003 1:52 AM User is offline

Hey Mitch,
I thought I would throw this out for discussion and maybe in confirming how I think the POA valve works others will benefit. Basically I equate a POA valve to a Backpressure Regulator on a refrigeration system. The valve maintains a backpressure in the evap to prevent freeze up of the evap coil but to allow the maximum amount of cooling by keeping the evap pressure at or slightly above the P/T curve for 32 degrees. This is also why readjustment of the valve is necessary when switching from R-12 to R-134. There is a few psig difference in the pressure at 32 degrees. The TXV will maintain the 10 degrees or so superheat of the refrigerant by shutting or opening as necessary based on load and the POA will maintain a constant pressure. I understand why this is a good system if you have one that is working correctly. Let me know if any of this thought process is incorrect.

Mitch on Sat September 06, 2003 11:33 AM User is offline

You are correct. The POA is essentially an evaporator pressure regulator that prevents the evap pressure from going below its setpoint thus preventing evap freeze up.

Some confuse the TXV with that function, but the TXVs sole purpose is to keep the evap full of refrigerant with the evap outlet at the superheat setting of the valve. The TXV cannot regulate evap pressure.

ddsmith on Sat September 06, 2003 2:47 PM User is offline

Guess I'll test that POA I was getting ready to throw away. If it test good I'll save it for future use. Do you have a higher resolution picture of the internals. If you do can you send it to me at [email protected] I may have to cut this one open also if it doesn't test good. Maybe I'll do the rebuild and TIG it back together to see how it works. Thanks,


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