Test AC Clutch / Compressor

mjonesjr84

mjonesjr84

WTF was that?
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Salem, IN
The AC in my 2000 doesn't work. The PO put in a new pressure switch on the dryer, but said it never worked after that either. I've tried jumping the high and low pressure switch wires and the clutch doesn't engage. Could the problem just be the clutch? If so, is that a serviceable part or does the entire compressor need changed?
 
Yes the clutch can be replaced separate from the compressor. First though check for power at the connector, you'll have to have the key on, the dash switch on and the LP switch connector jumped.
 
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mjonesjr84 said:
The AC in my 2000 doesn't work. The PO put in a new pressure switch on the dryer, but said it never worked after that either. I've tried jumping the high and low pressure switch wires and the clutch doesn't engage. Could the problem just be the clutch? If so, is that a serviceable part or does the entire compressor need changed?
Click to expand...

Check the pressures in the system, if there is no refrigerant then clutch won’t turn on. That is where to start.
 
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NskLJ said:
Check the pressures in the system, if there is no refrigerant then clutch won’t turn on. That is where to start.
Click to expand...

Actually jumping the LP switch will allow the clutch to engage even if there is zero charge. You have to jump it anyway to get the system to pull in refrigerant.
 
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Jumping either the low or the high pressure switch won't engage the clutch. I'll have to verify that it is getting power tomorrow.
 
It's a pretty simple system. When you switch the dash switch to AC it sends a ground signal thru both pressure switches to the PCM along with a second wire with a ground signal to the PCM. When the PCM gets both ground signals it connects one of them to the clutch relay which in turn energizes the clutch. The clutch relay coil gets it's power from fuse #11 in the fuse block and the power to the clutch coil comes from fuse #21 in the PDC. The PCM can delay the signal for up to 30 seconds under certain circumstances.
 
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Connect gauges to the system and see what the stabilized (off) system pressure is.
If the outside air temperature is 70* the refrigerant pressure should be 70 psi.
IF the PO replaced the LPCO and the clutch did not engage; there probably are problems with the A/C controls.
 
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B1Toad said:
Actually jumping the LP switch will allow the clutch to engage even if there is zero charge. You have to jump it anyway to get the system to pull in refrigerant.
Click to expand...

Yes you can jump it with zero charge but if it turns on then what? Still need to check the pressure. Refrigerate in the system carries the oil to lubricate the system. Actually you don’t need to jump it to charge the system.
 
B1Toad said:
It's a pretty simple system. When you switch the dash switch to AC it sends a ground signal thru both pressure switches to the PCM along with a second wire with a ground signal to the PCM. When the PCM gets both ground signals it connects one of them to the clutch relay which in turn energizes the clutch. The clutch relay coil gets it's power from fuse #11 in the fuse block and the power to the clutch coil comes from fuse #21 in the PDC. The PCM can delay the signal for up to 30 seconds under certain circumstances.
Click to expand...

That ALL is assuming the A/C console control switch, fan speed controls and mode selector are working properly with no electrical problems which they are prone to…
 
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CharlesHS said:
Connect gauges to the system and see what the stabilized (off) system pressure is.
If the outside air temperature is 70* the refrigerant pressure should be 35-45 psi.
IF the PO replaced the LPCO and the clutch did not engage; there probably are problems with the A/C controls.
Click to expand...

I'll hook up some gauges tomorrow.

The HVAC controls got replaced 2 weeks ago. The system wasn't working before either.
 
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CharlesHS said:
Connect gauges to the system and see what the stabilized (off) system pressure is.
If the outside air temperature is 70* the refrigerant pressure should be 35-45 psi.
IF the PO replaced the LPCO and the clutch did not engage; there probably are problems with the A/C controls.
Click to expand...

The pressure should be about 70 at 70 degrees outside temp. You are thinking of low side pressure running
 
mjonesjr84 said:
I'll hook up some gauges tomorrow.

The HVAC controls got replaced 2 weeks ago. The system wasn't working before either.
Click to expand...

Here is the diagram for a 99 tj. The pcm needs a ground at the signal from the switch and through the pressure switches to apply a ground to the
Relay.

IMG_0652.png
 
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NskLJ said:
Yes you can jump it with zero charge but if it turns on then what? Still need to check the pressure. Refrigerate in the system carries the oil to lubricate the system. Actually you don’t need to jump it to charge the system.
Click to expand...

Yes true but the original question was about the clutch, you can prove the clutch works or doesn't work without running the system. Many DIYs don't have the ability to check the pressure.
 
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Fairly certain this might be one of the issues. Wonder if this could have locked the compressor. This was with the engine NOT running and the AC switch off.

20240324_133351.jpg

I still need to jump the low pressure switch and see if I'm getting power on the AC clutch.
 
mjonesjr84 said:
Fairly certain this might be one of the issues. Wonder if this could have locked the compressor. This was with the engine NOT running and the AC switch off.

View attachment 512050

I still need to jump the low pressure switch and see if I'm getting power on the AC clutch.
Click to expand...

Looks like you don't need to jump the LP switch unless you think it's no good, there's enough pressure there to keep it closed and looks right on the money per @CharlesHS and @NskLJ. Time to start ringing out the circuit, maybe start at the relay and see if it's closing. Assuming you checked both fuses.

If the relay closes then move toward the compressor, if it doesn't move backwards thru the pressure switches and dash controls. Hopefully it's not the ECM but that's fixable too.
 
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