A/C problems

[SMalafy]

Can any one out there tell me if you will get electrical current to your compressor plug end with the ignition and A/c switches both on. I went to a shop and the guy just put gauges on the truck said the pressure was normal and my compressor was toast. He did not check any thing electrical and I do not think he knows what he is doing. I tried testing that way but got no current to the compressor plug.

 

[Timd32]

Maybe he saw/heard the compressor clutch operating but no change in pressures?

Other then that yeah would be tough to diagonse an electrical compressor clutch problem with out actually checking electrical stuff.

If the clutch is working and he was watching pressures not change maybe thats how they got to that assumption that its a compressor issue not a electrical issue.

You are actually looking for voltage not current, so if you are using a DVMM you would use the leads in the DC Volts mode not the Amps mode or use a test light. My compressor is a pain to get to the connector if I remember, so its not the easiest place to check from what I remember with the truck running. My 96 is a pretty basic AC circuit, not sure how much they changed year to year.

 

[fest3er]

They're all a 'basic' circuit. B+ to ignition switch to dash switch to PCM relay to low pressure switch to high pressure switch to compressor. My PCM relay failed years ago; the A/C shop bypassed it and the circuit's been fine ever since. (The PCM relay lets the PCM choose to disable the compressor under WOT. But this is for under-torqued engines that need that extra bit of power to mke it up hills; the over-torqued Cummins doesn't care.)

(Hint: your PCM relay could've failed....)

 

[SMalafy]

Maybe he saw/heard the compressor clutch operating but no change in pressures?

Other then that yeah would be tough to diagonse an electrical compressor clutch problem with out actually checking electrical stuff.

If the clutch is working and he was watching pressures not change maybe thats how they got to that assumption that its a compressor issue not a electrical issue.

You are actually looking for voltage not current, so if you are using a DVMM you would use the leads in the DC Volts mode not the Amps mode or use a test light. My compressor is a pain to get to the connector if I remember, so its not the easiest place to check from what I remember with the truck running. My 96 is a pretty basic AC circuit, not sure how much they changed year to year.

That is what I was using is a test light. The compressor was not working as I had a 95 truck before this one and I could hear the clutch go in and out. Thanks for getting back. I guess I will have to check out everything electrical with a meter as the manual says.

 

[SMalafy]

They're all a 'basic' circuit. B+ to ignition switch to dash switch to PCM relay to low pressure switch to high pressure switch to compressor. My PCM relay failed years ago; the A/C shop bypassed it and the circuit's been fine ever since. (The PCM relay lets the PCM choose to disable the compressor under WOT. But this is for under-torqued engines that need that extra bit of power to mke it up hills; the over-torqued Cummins doesn't care.)

(Hint: your PCM relay could've failed....)

Thanks for getting back. I just wanted to make sure I should of had power in the plug going to the compressor so now I will try and find it myself by going thru everything electrical and if no problems there it would probably be the PCM relay

 

[Timd32]

When the PCM relay is picked up you should have power to the plug.

The dash controls (AC or Defrost) then the ac pressure high and low switches, all CLOSED send the request to the PCM, the PCM then picks up the relay to drive the compressor clutch.

You should have a light when its calling for AC and the pressure switches are CLOSED.

Then of course need to make sure you have a neg @ the compressor circuit.

Only reason I mention the volts vs amps mode on a dvmm they are different position for the leads, you wont see anything in amps mode with out being in series with the wiring which is very hard to do, and not needed 99.9% of the time.

Test light would be fine for these checks.

 

[DavidC]

Probably just the picture you had but the meter is on AC volts, need to turn up 2 notches for DC.

Dave

 

[Timd32]

Probably just the picture you had but the meter is on AC volts, need to turn up 2 notches for DC.

Dave

Correct.

I was working on a oven at church today. Did not look at that.