Ac electrics

[Sterling]

My ac has never worked so I tested the pressures. 0! so I found the accumulator leaking and replaced it. I evacuated the system and began filling it but the compressor will not engage. If I disconnect the compressor plug on the supply side I have 0 volts between the pins but 13 v from one pin to the frame/ground. I am guessing there is a loop through the compressor to the high pressure and low pressure switches. Am I right or is there some logic board involved. I am guessing the low pressure is in the accumulator should it be closed with pressure? The high pressure is right off the compressor should it be closed during normal operation? Basically can I paper clip the switches to diagnose?

 

[dudeman2009]

The compressor clutch is controlled by the PCM based on the pressure switch inputs. The pressure switches are in series with each other, both are closed in normal operation. Low side is normally open, when the pressure rises the switch closes, the high side is normally closed, when the pressure rises it opens. You can jumper them, but make sure you watch the low and high side pressures, if it goes too high it can blow out lines and fittings on the high side, if the low side goes too low, it can cause the compressor to burn out.

On the compressor side, if you have battery voltage on one side of the connector, then the PCM is trying to turn the compressor clutch on. You dont have an issue with the pressure switches, dont even mess with them. The pin that has 13v to ground is the source pin, the other pin is ground. Check the other pin for continuity to ground, if it reads open, then you need to repair the ground.

 

[Sterling]

Thanks

I just went back out and no longer get any voltage on either pin on the compressor connection.

I tried jumping out everything kinda ***** nilly. I have 12 v at the ac compressor relay on the cool side. I jumped the load ( 30 and 87) but still no voltage at the compressor.

The 10 amp ac relay fuse is good and I have voltage at 30

The compressor coil has resistance but it does seem to jump about.

To jump everything I would jump the low and high and jump 30 to 87 on the relay, correct? If this fails it's the compressor clutch?

Thanks so much

 

[Sterling]

It just dawned on me that you said one side of of the compressor connector is ground so there should continuity to the frame. If I don't have that the compressor won't engage.

I know the truck is old and the connector is in a hot spot. I wonder if me jerking around broke the connector? So one side to ground and can I check the other to the relay?

 

[dudeman2009]

It just dawned on me that you said one side of of the compressor connector is ground so there should continuity to the frame. If I don't have that the compressor won't engage.

I know the truck is old and the connector is in a hot spot. I wonder if me jerking around broke the connector? So one side to ground and can I check the other to the relay?

To test the clutch, jump one pin to ground and the other to battery positive with jumper wires. That will tell you pretty quick if the clutch is bad.