1971 Chevy PU 134 change over problems

Cautrell05 on Wed May 27, 2015 2:21 PM

Year: 1971
Make: Chevy
Model: C10
Engine Size: 350
Refrigerant Type: 134
Ambient Temp: 65
Pressure Low: 40
Pressure High: 200
Country of Origin: United States

Customer vehicle. 71 Chevy all original. replaced compressor with a GM unit. A6 I believe, the 50 pound version. Old compressor had a rough bearing. also replaced the expansion valve and the dryer as well as all three rubber lines. Can not get it to cool. Heater hose has a ball valve in it, hoses are cold with engine warmed up. Heater door apperars to be in the closed position. The charge tag on the old compressor said 4 1/2 pounds. Tried different charge amounts from 2.5-4.5 pounds. Most temp drop from ambient is 5 degrees, maybe 10. 55 degrees at the vent with the engine at high idle and fan on high. read in a few placed about adjusting the poa valve for 134. General consensus is 1/4-1/2 turn counter clockwise when viewed from the outlet side of the valve. Tried 1/4, 1/2, and 3/4 turn out with out much change. with the ac on, high idle and blower motor unhooked low side pressure is around 35psi. What am I missing and where too next? For the amount the customer is spending to get this fixed I am not happy with only 10 degrees difference with the air on. Thanks
Nick

Edited: Wed May 27, 2015 at 3:04 PM by Cautrell05

mk378 on Wed May 27, 2015 7:54 PM

Low side (before the POA) should drop to about 23 to 25 and regulate there with no heat load. After the POA (if there is a port on that side where you can measure) should be much lower. This is assuming the TXV is working properly. POA can be tested off the car with compressed air. Since turning the adjuster didn't do much, it is quite possible the POA is bad.

Edited: Wed May 27, 2015 at 7:55 PM by mk378

Cautrell05 on Thu May 28, 2015 12:41 AM

When I left for the day it was set at 1 1/4 turns out with 2# 12oz and getting 48 sitting still and 43 down the road with the outside temp close to 80. Low side at about 34 after the evaporator and before the POA. I have to pull it down in the morning anyway because of a leaking seal at the POA valve from the TXV. Going to try another 1/4 turn while it's empty and see what happens

Dougflas on Thu May 28, 2015 5:21 PM

POA should be at 26PSI with the blower motor disabled. When adjusting the POA, you have to make sure the adjustment does not change when tightening the nut. It is easier to do off the vehicle. I used to take a socket (1/4 inch drive), place it on the nut, and use a screwdriver in the middle of the socket to hold the adjustment screw while tightening the nut.

Cautrell05 on Thu May 28, 2015 6:54 PM

Quote
Originally posted by: Dougflas
POA should be at 26PSI with the blower motor disabled. When adjusting the POA, you have to make sure the adjustment does not change when tightening the nut. It is easier to do off the vehicle. I used to take a socket (1/4 inch drive), place it on the nut, and use a screwdriver in the middle of the socket to hold the adjustment screw while tightening the nut.

That might explain why im not seeing much change. I didnt see a spot for a screwdriver, only a hex. need to look at it closer when I have it off.

Cautrell05 on Sat May 30, 2015 10:28 AM