Year: 1971 vin
The EPR valve is nothing more than an EVAPORATOR PRESSURE REGULATOR valve. Its purpose to to keep the pressure of the evap regulated.
To test this system on the vehicle, run the vehicle to stabilize the system. The system must be fully charges. View the sight glass. You will need to use 3 gauges. Connect the high side and low side. The 3 rd gauge is connected to the fitting on the compressor head. This is a low pressure gauge.
Operate the engine at fast idle with AC set for max AC, high speed blower, temperature cable in the full reheat position. Close windows and operate for a few minutes to load the evaporator. High side MUST be between 140 and 210 psi.
Remove expansion valve bulb from socket in suction line. Place bulb in ice and water. Submerse bulb 5 inches and make sure that the water/ice is at 32ÃÂº. Low side gauge needs to be 21 to 25 psi. If the result is not 21 to 25, expansion valve is defective and needs to be replaced.
If the above happens(21 to 25), read the 3 rd gauge. It needs to be 17psi of less. If higher, EPR is bad.
If above passes(17) , remove TXV bulb and place it in your hand for a few minutes. Low side should go to a minimum of 40 psi. If this does not happen, TXV is bad and needs replacing.
If the low side is a min of 40, the 3 rd gauge should be 1 to 4 psi less than the low side. If the 3rd gauge reads more than 4 psi, the EPR is bad and needs replacing.
If the ERP and TXV check good and the system still does not cool well, thye possibility of the compressor valve plates may be weak.
The later EPR valves have a greater differential. With a suction pressure of 30psi or higher, the 3 rd gaguge should run 6 psi lower.
I did not write this article. I have copied it from an old Mitchell manual. Give them the credit. :-)
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