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Discussion Starter · #1 ·
Ok, why is it there.Why complicate the system,it already has a metering valve(expansion).The poa is not sold new or rebuilt,are they a common problem source?I called my AC suplier,they said to install a update kit.I understand the kit replaces the POA,and just connects the suction side,with nothing inside the connector. I've worked on these (POA) before,but never understood the reason for the POA valve.
 

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The POA valve maintains the pressure in the evaporator at 28.5 PSI. The thermal expansion valve keeps liquid refrigerant from entering the evaporator by providing the pressure drop from the compressor discharge side of the system which operates somewhere in the 200 PSI range. The liquid flashes to vapor as it passes through the expansion valve, while the POA valve maintains the pressure inside the evaporator at a pressure which corresponds (when using R-12)to the a temperature of 30 degrees F.

This is the component that causes R-134a to operate less efficiently in a retrofitted system. Since the POA valve is non adjustible, when a system is retrofitted with R-134a the temperature of the refrigerant is increased in the evaporator to about 35 degrees F instead of 30 degrees F. This inturn raises the operating pressure of the entire system somewhat.

If you remove the P.O.A. valve there will be no way to control the pressure within the evaporator except with engine RPM, since the compressor is essentially a positive displacement pump (pumps the same amount of refrigerent per revolution regardless of operating conditions) at low engine speeds the pressure in the evaporator woould increase, raising the temperature of the refrigerant in the evaporator and at high engine speed lowering the temperature or the refrigerant resulting in freezing of the evaporator.

The POA valve is the large component that is connected between the outlet of the evaporator and the hose going to the compressor, with the service ports in it. You can't just hollow it out and screw it back onto the evaporator.

Don't fool with the A/C system components, they are there for a reason. If someone made an adjustable POA valve or one set to 26.5 degrees (they don't) then it would be worth it for use with R-134a.


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Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11
 

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Discussion Starter · #3 ·
I'll be running R12,or freeze 12."The POA maintains low (cold) evap. press.,even at idle".Cant the exp valve do this,opening up when at high speed,closing at low speed.Therefore maintaining evap pressure,on it's own?Well I think I've got this all wrong,I'll have to hit the books on this one.If there were only an exp. valve,with a pos. displacement pump,then at high volume(speed),you would need the exp. valve to open, or high side press. would be too high,and low would be too low.Well I'm rambling,and am still in a fog on this one.But, I so far am unable to buy a new or rebuilt POA valve,what to do? The supplier of the "update kit" says that the POA system does'nt work in AZ.it's [email protected] in the summer

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68 z28 ,68 rs 327 ,73 454 vette, 2 goofy kids
 

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There is a BB similar to this at http://www.aircondition.com Someone there may be able to help.

BTW- 2 summers ago I bought a POA from YearOne,. It was for my el camino, but I bet they are the same. Its possible that they may still have one. And with 134 I have no problems staying cool. West Texas is not quite as hot as Az, but I bet its close.


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Rick Schaefer
68 Camaro
72 El Camino
TPI350/700r4
 

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Discussion Starter · #5 ·
Thanks

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68 z28 ,68 rs 327 ,73 454 vette, 2 goofy kids
 
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