Looking for some A/C troubleshooting tips

[Petethepug]

Alright, double secret probation then.

[dkfx]

I had the same issue, and when I charged my a/c (to test if the system even worked) I heard a nice hiss coming from behind the driver side headlight when the car was off. It was leaking right at the AC pressure switch which is right above the accumulator / drier.

FCP Euro has the part for under $10, but was able to order it on amazon for $13 and have it the next day. If you want to search for it they have it labeled as the "Four Seasons 35758 System Mounted Low Cut-Out Pressure Switch". It was a BEAR to remove, and it's MUCH easier to pop up the driver side headlight to get to the fitting. Mine was so corroded (probably original) I had to use locking vice grips to remove, but the new one slid right in... and fixed my A/C leak.

Now to fill up and test again to see if I have any other leaks before doing a full evac and charge.

(not sure if image is working but here is what mine looked like) https://photos.app.goo.gl/pabDwdVA7yNMvgA16

[blueline]

@dkfx

Your pic didn't post. However, photo posting is encouraged and greatly welcomed here and is very easy using the following guide:
viewtopic.php?t=410

And, welcome to Carpokes!

[notny41]

ok guys I'm finally getting around to doing some troubleshooting on this.

I pulled the two black/red wires off my low pressure switch and tested continuity across the switch with the engine off. it tested as a closed circuit so that's good I'd imagine. I take that to mean that my system is pressurized.

so then the next thing that I did was to hook up a switch onto the ends of the red and black wires and start the car up, put air on, fan on, temp to cold, and went back-and-forth between open and closed on the switch I plugged into the harness connectors. The compressor still did not start up when the switch was in either position, but I did notice the RPMs on the car increase when I closed the switch, even though the compressor clutch did not engage.

So looking for next steps here. I suppose it could need a new compressor but I'd like to be sure that's my problem before swapping that out. Did someone mention hard wiring the compressor somehow - bypassing all other wiring?

[dr bob]

There are a few basic electrical tests you can do before replacing the whole compressor.

-- Most basic is connecting a voltmeter or even a simple test light to the wire from the car to the compressor. Single conductor, usually a spade connector somewhere close to the compressor. You can unplug the compressor and look for circuit voltage when you expect the compressor to run. (key on, AC button engaged, etc.) If you see battery voltage there referenced to ground, there's power available to close the clutch coil and run the compressor. If not, you are tracing circuitry back towards that pressure safety switch and onward to the fuse.

-- If you do see battery voltage there, you can move your meter to the wire from the clutch, and test resistance from there to ground. The coil resistance is in the 3-5 Ohms range IIRC, referenced to ground. If you don't see that, look carefully at the wiring to the clutch coil. Look hard at the one you are testing, plus one from the coil to the compressor body behind the pulley and clutch.

-- You can do a test of the clutch coil and clutch by running a battery+ jumper to that terminal. Engine stopped. The coil should draw the clutch closed with a very noticeable clink sound, and you can watch the rear disk in the pack get pulled to the coil when that happens. If not, the clutch is DUFO.

-- I'm not familiar enough with the specific compressor control on your car. On the 928, the system relies on a too-small relay actuated by the dash controller AC button. Circuit continues from that relay through an anti-freeze switch on the evaporator, then on to the pressure safety switch before feeding the clutch coil. So testing for function starts with the easy connection at the clutch coil, then moves to the pressure switch, the anti-freeze temperature switch, and finally the relay and contact in the dash controller. This is in the 928, and is a convenient but less than ideal circuit design. The relay should be the last thing before the clutch coil. Maybe the 944 guys were smarter than the 928 guys. Best to check your model-specific wiring diagrams for the exact sequence for testing.

@Tom knows this stuff intimately. Hopefully he'll jump in and correct my mis-info. I've had just about zero 944 exposure, so take my suggestions with one large and two small grains of salt.

[Tom]

There are a few basic electrical tests you can do before replacing the whole compressor.

-- Most basic is connecting a voltmeter or even a simple test light to the wire from the car to the compressor. Single conductor, usually a spade connector somewhere close to the compressor. You can unplug the compressor and look for circuit voltage when you expect the compressor to run. (key on, AC button engaged, etc.) If you see battery voltage there referenced to ground, there's power available to close the clutch coil and run the compressor. If not, you are tracing circuitry back towards that pressure safety switch and onward to the fuse.

-- If you do see battery voltage there, you can move your meter to the wire from the clutch, and test resistance from there to ground. The coil resistance is in the 3-5 Ohms range IIRC, referenced to ground. If you don't see that, look carefully at the wiring to the clutch coil. Look hard at the one you are testing, plus one from the coil to the compressor body behind the pulley and clutch.

-- You can do a test of the clutch coil and clutch by running a battery+ jumper to that terminal. Engine stopped. The coil should draw the clutch closed with a very noticeable clink sound, and you can watch the rear disk in the pack get pulled to the coil when that happens. If not, the clutch is DUFO.

-- I'm not familiar enough with the specific compressor control on your car. On the 928, the system relies on a too-small relay actuated by the dash controller AC button. Circuit continues from that relay through an anti-freeze switch on the evaporator, then on to the pressure safety switch before feeding the clutch coil. So testing for function starts with the easy connection at the clutch coil, then moves to the pressure switch, the anti-freeze temperature switch, and finally the relay and contact in the dash controller. This is in the 928, and is a convenient but less than ideal circuit design. The relay should be the last thing before the clutch coil. Maybe the 944 guys were smarter than the 928 guys. Best to check your model-specific wiring diagrams for the exact sequence for testing.

@Tom knows this stuff intimately. Hopefully he'll jump in and correct my mis-info. I've had just about zero 944 exposure, so take my suggestions with one large and two small grains of salt.

What he said.

In an effort to add a morsal of value, here's a picture of the compressor spade. Very weird design in that the spade is wedged on there very tight, yet there's no good way to grab it and yank it out -- so good luck with that. Bob's test all carry over to the 944 perfectly up to the control circuit part -- we have the infamous climate control unit. I'd start by pulling the spade connector off (good luck) and running a single jumper cable from the positive terminal of the battery to the spade connected to the compressor (NOT THE HARNESS SIDE). The clutch should engage hard. If not, whatever DUFO means, the compressor is that. (Due for overhaul? Definitely Un-Fixable Object? Dead Until Funding Occurs? Doesn't Understand Fan Orders?)

[notny41]

much thanks guys! that is what I'll do next. thx for the pic @Tom and I think I saw that if the clutch coil is not within ohms and not sucking the pulley in, a person can change just that coil without pulling the compressor out of the system.

This is the type of stuff where I'm glad I have a lift in my garage!