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LPCO Switch adjustment

y2k600f4 on Sun September 07, 2008 9:18 PM User is offline

I had a question on the proper pressure for the LPCO to be set after a R12 to R134 retrofit. I have read 1/4" CCW should do it (~drop of 3 degrees). However I have also read that is should be adjusted to 19F and others recommending 25F ????

With the LPCO connected will you see a drop in the low side pressure while adjusting the switch ?

Edited: Sun September 07, 2008 at 9:31 PM by y2k600f4

GM Tech on Mon September 08, 2008 9:25 AM User is offline

The switch monitors the pressure... the pressure does not change with switch setting... that is a function of heat load on the evaporator. So by adjusting the switch, you are changing the pressure at which the compressor will be shut off at- hopefully to avoid freeze-up-- that is why there is a low pressure switch in the first place.. If you want to test the cut-off point, then unplug the blower motor, or run it on the lowest fan speed, or choose a cool night to test it-- the less heat across the evap face, the lower the pressure, the more likely the evap will get coldest, and the switch will turn off the compressor at whatever set point you have dialed in.

You must have a fairly old system, adjusting cycling switches went obsolete in the early '90's.......

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

y2k600f4 on Mon September 08, 2008 3:05 PM User is offline

GM Tech....thanks for the clarification.

Actually the car is an 1980 Camaro.....just trying to determine what I should set the LPCO swith at ? I am guessing around 25F ?

GM Tech on Mon September 08, 2008 3:07 PM User is offline

awwww... go for about 22 psi -- see if that works without freezing....

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

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