97 Expedition 5.4L AC issue - just need verification

[Firekatt]

Hi everyone,

So, I picked up a used expedition and finally got her running good so now it's time to move on to the other things...namely the AC. I have very limited tools and also very limited funds but here's what I've done so far....

Pulled the connector loose from the low pressure switch and jumped across to see if the compressor would kick on - nothing

Pulled the connector from the high pressure switch and jumped across it - nothing

Took my little hose and added a bit of R134 with engine running and AC on max - nothing

Pulled the low pressure connector again and ran a wire from the positive battery terminal to the Black/Yellow stripe wire with everything off, including the key, again - nothing happened

I can't think of anything I may have missed to try and get the compressor clutch to engage and I didn't pull the connector loose from the compressor itself as it's a pain to get to and to see so as to make sure I'm not hitting the ground wire terminal by trying to put power there. So, this leads me to believe that the compressor clutch is bad. The compressor turns by hand so I know it's not froze up or anything.

Any other thoughts? also, if the clutch is my problem, can it be changed on the truck or do I need to pull the compressor completely off to change it?

Thanks in advance

 

[stamp11127]

Check for voltage at the low pressure switch. Also check the air gap on the compressor clutch. If it is too much it won't engage.

 

[docraymund]

Apply 12 volts directly to the compressor clutch terminal with a fused jumper wire and see if it kicks on.

 

[Firekatt]

I did some checks and do have voltage at the low pressure switch. Also, the air gap on the clutch seems to be fine. Nothing is bent or out of shape and it doesn't look like it's ever been changed. I would like to put 12V directly to the compressor terminal but it's in a location where I can't really see what I'm doing to make sure I'm not touching the ground terminal as well...or both at the same time. Also, just putting voltage to the correct terminal doesn't seem like it would work since it seems the clutch has a ground besides through the compressor body...otherwise, why would it need a ground wire too?

 

[Ed G]

I'm pretty sure you need to apply voltage to the proper terminal on the clutch to magnetize it. I do not think you'd have a path to ground if you applied voltage to the ground side. You mentioned the compressor terminal, what do you mean? sometimes there'd a pressure switch built into the compressor, otherwise its only clutch wires. In my experience the compressor is a simply mechanical device, nothing electrical happens it it, it only turns and works when the clutch is engaged.

 

[Firekatt]

Sorry, I should be more clear. I do mean the wiring connection that goes into the clutch. It's towards the top, passenger side of the truck at about the 10 o'clock position (looking at the compressor from the front) and the hoses run right over it. Hard to reach down and still see what I'm doing and also can't see at all from underneath. Also, pulling the connector apart seems to mean I also need to ground it while putting power to the right terminal since it seems it needs an external ground to work. I did put a test light to the wires on the low pressure switch and had power in both wires (Engine running and AC turned on inside) so I do know the switch is working and probably also means the system is charged. It seems I have a bad clutch but I don't have the tools to evacuate, pull a vacuum and then refill. Since my wife was in a car accident a couple of weeks ago, I can't afford for a shop to do this either. Can this clutch be changed with the compressor still on the truck?

EDIT: Everything cooled down enough so I went to take another look. I was able to disconnect the connector to the clutch and had power on 1 side, none on the other. I reversed my test light to check the ground side and everything there was fine as well. From this I gather the field coil in the clutch is bad. Again, can this be changed on the truck?

 

[stamp11127]

Depending on the age of the compressor you risk damaging the compressor seal replacing the clutch. Not worth the hassle to me.