73 olds 455 A/C evaporator temperature sensor
May 1st, 2014, 07:14 PM
#4
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Thread Starter
Join Date: Jan 2011
Posts: 57
As you guys can tell I'm sure no A/C expert but there has to be something to signal the compressor that it's time to shut off or the lines will freeze. That's what I'm looking for. Air blows ice cold when I start it up then after a couple minutes the low side freezes, I can turn it off manually and it will thaw and start the process all over again. Any help on this appreciated, thanks.
May 1st, 2014, 07:50 PM
#5
Connoisseur d'Junque
Join Date: Sep 2010
Location: The Hudson Valley
Posts: 21,183
The original Frigidaire system does not shut the compressor of unless you shut the A/C off.
The compressor pressurizes the refrigerant, which is cooled in the condenser and condenses into liquid, then it flows to the expansion valve, where it is metered into the evaporator, with the quantity allowed in dependent on the evaporator outlet temperature. In the evaporator, the liquid refrigerant sprayed in by the expansion valve is able to expand and turn into a gas, picking up heat along the way. After leaving the evaporator, the refrigerant passes through the POA valve, which maintains the pressure in the evaporator at 29.5 psi, which, in concert with the expansion valve, keeps the evaporator from dropping below freezing. After the POA valve, the refrigerant goes back to the compressor, where it is pressurized and pumped to the condenser again.
If you are getting low side icing, you could have an expansion valve that is stuck open, allowing too much refrigerant in, or you could have a POA valve that is stuck open, allowing the pressure in the evaporator to go too low.
The POA valve is easy to test, and we were all trying to find Rob's excellent post on the subject, but nobody could.
Primary information about testing is here, and some additional information here.
The expansion valve cannot be tested, but you may get lucky and find debris in its intake screen, or other evidence that it's not working right.
- Eric
The compressor pressurizes the refrigerant, which is cooled in the condenser and condenses into liquid, then it flows to the expansion valve, where it is metered into the evaporator, with the quantity allowed in dependent on the evaporator outlet temperature. In the evaporator, the liquid refrigerant sprayed in by the expansion valve is able to expand and turn into a gas, picking up heat along the way. After leaving the evaporator, the refrigerant passes through the POA valve, which maintains the pressure in the evaporator at 29.5 psi, which, in concert with the expansion valve, keeps the evaporator from dropping below freezing. After the POA valve, the refrigerant goes back to the compressor, where it is pressurized and pumped to the condenser again.
If you are getting low side icing, you could have an expansion valve that is stuck open, allowing too much refrigerant in, or you could have a POA valve that is stuck open, allowing the pressure in the evaporator to go too low.
The POA valve is easy to test, and we were all trying to find Rob's excellent post on the subject, but nobody could.
Primary information about testing is here, and some additional information here.
The expansion valve cannot be tested, but you may get lucky and find debris in its intake screen, or other evidence that it's not working right.
- Eric
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