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How does a POA valve work?

dwg on Wed June 24, 2009 9:45 PM User is offline

Year: 1967
Make: chevy
Model: impala
Engine Size: 283

How does a POA valve work?

My understanding is that the A-6 compressor is running continuously whenever the A/C is selected, How does this constant running not ice up the evaporator, or make the car so cold you can't stand it? Is this a function of the POA valve?

Is there a good schematic diagram of how the refrigerant flows in this old system?

If I am not understanding the way this system works, can someone explain it? I have a basic understanding of the liquid and the gas, and the functions of the evap and the condenser, but I don't really follow how the system throttles itself up and down to maintain a temp.

Thank you for your help

mk378 on Thu June 25, 2009 9:49 AM User is offline

The POA regulates pressure in the evaporator by restricting the flow out of the evaporator should evaporator pressure get too low. By holding the evaporator pressure up, this increases the boiling point of the refrigerant to more than 32F, which makes it impossible for the evaporator to get cold enough to ice up.

Otherwise it is a standard TXV system, it just has the throttling valve in line between the evaporator and compressor. The pressure on the compressor side of the POA valve will vary with rpm etc and will always of course be lower than evaporator pressure.

Like most systems, the evaporator always runs at a constant 40 F or so. If the dash controls are set for warmer than maximum cooling, some of the air is reheated in the heater core.

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