Swapping the Clutch on an R4 A/C Compressor

[PlayingWithTBI]

I've had good luck with Permatex Orange 25210

Thanks, I might try that.

 

[Erin]

Mine's quiet and the air gap is still ~0.020". It's not very old either.

I ended up getting a refund from Rock Auto, since it was the second one from them to seize up, and bought one off amazon.

 

[Schurkey]

Because, when I rev it up it doesn't suck down the low side (it just wavers between 35 & 40 IIRC) or increase pressure on the high side...
I should be able to look at the clutch for signs of over heating or damage... ...That leads me to thinking the clutch is slipping. I'm going to ohm out the coil and compare it to my spare one too.

Verify that the clutch coil is getting proper voltage/amperage.

I'd want to know the voltage at the clutch terminals--power and ground--with the clutch engaged.

The ground side should have essentially zero volts. Any more than zero is likely the result of a poor ground.

The supply side will "want" about system voltage, I think. Maybe system voltage minus one volt or so. This might be listed in the service manual. If the voltage is down more than a couple of volts, you've got excess resistance on the supply side of the circuit.

 

[PlayingWithTBI]

The supply side will "want" about system voltage, I think. Maybe system voltage minus one volt or so. This might be listed in the service manual. If the voltage is down more than a couple of volts, you've got excess resistance on the supply side of the circuit.

Thanks. That's funny, I was thinking about that and wondering if I ought to throw a relay on it to get full battery voltage. I'll check it out and let you know.

 

[PlayingWithTBI]

The supply side will "want" about system voltage, I think. Maybe system voltage minus one volt or so. This might be listed in the service manual. If the voltage is down more than a couple of volts, you've got excess resistance on the supply side of the circuit.

I got out my meters, a Fluke and An HEI, just to see how close they were to each other. The HEI was reading about onE Ohm higher than the Fluke using the same leads and crossing them to see how close to zero they would go. The Fluke read 0.2 Ohms while the HEI read 2.7Ohms. I changed the batteries - the HEI was from 2008, ha ha. I don't use that one very often, mainly for testing capacitors. Anyway, back to the story.

My spare coil and the one in the truck are within a 1/10 of an Ohm, ~3.7. I put in a couples jumpers to check voltages. With truck running and A/C on, I got 11.4V at the compressor with 14.2V at the battery, 2-1/2V difference. Who knows, 11.4 Volts may be enough but, like I said above, I'm gonna install a relay so I can get full system voltage at the compressor coil. I might just tap off the alternator, ground at the T-Stat housing, and use the wires from the coil to activate the relay which will be mounted close to the compressor. I wonder if it will be too hot for the relay there or, should I mount it on the wheel well behind the battery and run a wire loom around to the compressor?

 

[Schurkey]

I wouldn't expect heat to be a major problem, but mounting the relay far enough away from the compressor wouldn't be a problem, either.

Take a look at your existing wiring. I suspect you'll have a capacitor across the + and - wires; probably tucked under some tape right at the molded plug that connects to the clutch coil.

Be sure that your relay includes a similar capacitor, or add one of the same values (capacitance and voltage) of the OEM unit.

This prevents voltage spikes transmitted to the rest of the vehicle.

"I" would be running a jumper wire to the clutch coil, to see if more voltage resulted in better performance before taking anything else apart.

It might be worth your time to trace the wire harness back, to see if there's a point of high resistance that could be repaired, rather than installing a relay.

 

[PlayingWithTBI]

Take a look at your existing wiring. I suspect you'll have a capacitor across the + and - wires; probably tucked under some tape right at the molded plug that connects to the clutch coil.

Yes, now that you mentioned that, there is a diode, IIRC.

It might be worth your time to trace the wire harness back, to see if there's a point of high resistance that could be repaired, rather than installing a relay.

You know how brittle wires and looms are on a 32 year old truck, LOL. I'd prefer to exacerbate the condition as little as possible

 

[Schurkey]

Well, crap. Diode, not capacitor.

I sometimes think I've achieved early senility.

 

[PlayingWithTBI]

I sometimes think I've achieved early senility.

I gotcha beat in that category, LOL.

 

[PlayingWithTBI]

I decided to go ahead and do it. I rounded up some supplies.

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Drew a little schematic

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And wired it up.

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To be continued...