Chasing a lack of cold air in the cabin, I have found myself at the compressor itself... I've got voltage (verified with a test light) at the 2-pin compressor connector when the A/C is switched on, which tells me the panel **** is functioning and the relay and low pressure switch are OK. The two pins on the compressor itself do not have continuity between them, and neither has continuity to ground either. My DVM shows 3.7ohms between the pins. I guess now I'm not sure what to check for? The clutch simply isn't grabbing, and thus not cycling the compressor?

 

Try taking off the connecting pin and run a wire from the positive side of the battery to one pin and a second wire from the negitive side of the battery to the other pin on the compressor. It the clutch doesn't engage then the compressor is bad. If it does then the problem is some place else.

 

Your post is kind of confusing. You say there is no continuity between the pins, then you say there is 3.7 ohms between the pins.

If you have voltage on one side of the coil, and none on the other, this would indicate an open winding in the clutch assembly. This can be replaced without replacing the compressor.

Also, details of the truck would be helpful year, engine, etc. jd

 

3.7 ohms is just about right for a clutch coil. If you have 12 Volts to the coil, your concern is on the ground side. The vehicle information would help.

 

Details of the truck are in my signature, but maybe it doesn't show up properly for everyone? At any rate: 1994 F-350, 460 V8, Automatic, 4wd.

Let me first say that electrical work is NOT my strong suit!! If my post is confusing I apologize, but I checked each "test" several times with the same results (all of these is done with the harness disconnected at the compressor itself)

1.) No continuity between the two pins on the compressor itself
2.) No continuity between either of the two pins and ground
3.) 3.7ohms between the two pins

Again, each of these was done a half dozen or so times to verify, and I certainly don't know what any of it means or implies, thus my call for help

 

Connect your test light across the terminals of the clutch harness connector (ac on, truck running). It should light. If so:
With the truck running and the ac on, tap the clutch inward and see if it engages. If so, the gap is too wide. If not, the coil is open.

 

Will do, thanks for the input!!!

And just to be 100% clear, when you say "open", you mean it's bad and needs replaced? NAPA lists a replacement clutch coil, and also a whole replacement clutch/coil/pulley assembly for about the same amount of money. I'm guessing the wiser investment would be the combo kit?

 

Yes, OPEN means electrically open, no continuity. You mentioned about 3.7 ohms. That's about right for a good coil.
Tap on the clutch and see if it engages. The gap is adjustable with shims on the compressor shaft.
If your coil is actually bad, the kit is the best option. It's a pretty easy job.

 

Again, thanks for the reply! I'll check for power across the terminals at the connector and try tapping the clutch both this evening when I get home from work and report (~3 hours from now)...

 

You should have your test light lighting on one of the wires that connects to the clutch coil. If you dont, check for voltage at the low pressure cutout switch at the A/C evaporator. Someone here should be able to supply you with an exact location of this switch. Mine is an 83, and I bet its different from yours.

 

Allright, just checked things out again. Here is where I'm at now:

1.) With the truck running and the A/C switched on, I have power across the terminals of the plug going to the compressor (from the pressure switch?). This was verified with a test light, jumping across the two female ports on the harness plug. As expected, when the A/C was switched off in th cabin, power went away at the plug so I'm firmly convinced the problem lies at the compressor itself...

2.) With the truck running and the A/C switched on, I tried to tap the clutch and see what happened. Nothing... I tried several times with various hammers and various force, all with no result. There were a couple times where I hit the outside of the clutch/pulley rim and caused it to spin a few degrees, but it had nothing to do with actual electrical engagement...

3.) Because my initial "tests" were odd in that I showed no continuity between the terminals, yet also found 3.7ohms between them, I double checked both. This time, I did indeed find continuity between them and still show the same 3.7ohms between the pins on the compressor itself.

Sooooooo, again as stated I'm no electrical guru, and I'm at a loss here. I've got what appears to be acceptable resistance through the coil, and I've got what appears to be acceptable trigger power to the coil itself. But alas, it just won't grab?

 

Hmmmm, that's odd. If you have power across the connector and coil continuity......by golly, it should engage, even if you have to tap the clutch inward. You might have high resistance in the cycling switch or the AC relay contacts that allows the test light to light, but not enough current for the coil.
What year and model is the vehicle? I'll dig up the wiring diagram and have a look.
Just for grins, locate the cycling switch on the accumulator and jumper the connector with a paper clip. See if the clutch engages.

 

It's a 1994 F-350 with the 460 V8, automatic, 4wd...

When you say to jumper the connector, I simply need to unplug it from the accumulator and run a wire or something (paperclip?) from pin-to-pin?

 

Yep. Jump the 2 terminals in the harness connector. I;m not trying to oversimplify it, but I've had someone try this and they jumped the terminals on the switch.

 

Hey no worries, I *NEED* oversimplification on electrical stuff!! I appreciate you taking the time to walk me through it. I'll report later this evening when I get home.