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Old 07-25-2022, 03:21 PM   #1
mschultz373
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Default stuck AC clutch

the inner wheel on my AC compressor is not turning regardless of the AC being on or off. My AC was just working and then suddenly stopped blowing cold. It was blowing at 35F while driving beforehand.

This is what the compressor looks like with the AC on and the fan on; belt is turning and pulley is turning normally (no squeal/smoke/etc):
IMG-3298


is there a way to unstick the clutch so the AC will turn back on?
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Old 07-25-2022, 03:28 PM   #2
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First check whether the clutch is actually getting power. The pressure switch on the accumulator is an easy place to check for power. One terminal is for power coming from the AC control panel, the other terminal is power to the clutch after the pressure switch.
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Old 07-25-2022, 03:43 PM   #3
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hate to be total n00b but - where is the accumulator and pressure switch? On the compressor?

Wish I had a bentley manual for the 960!
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Old 07-25-2022, 03:50 PM   #4
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The accumulator is the Coke can like aluminum cylinder in front of the firewall on the passenger side of the engine compartment. You will see a switch screwed to the side of the cylinder with a two wire harness connected to it. That is the low pressure switch. If you have an ohmmeter, unplug the connector and probe the switch in the ohm setting. If you get something like 1-2 ohms, the system has enough refrigerant in it for the compressor to run. If you get infinite ohms/open circuit, the system it too low on refrigerant, or, the switch itself has failed.
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Old 07-25-2022, 04:11 PM   #5
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the fuse for the AC clutch is blowing. it was blown and the replacement blew in seconds.

the switch on the accumulator ohms out at 0, it seems. I got 0.1, which I doubt my meter is accurate enough to measure.

The harness to the switch was getting 3-4V on one side and no voltage on the other.
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Old 07-25-2022, 04:33 PM   #6
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It sounds like you have a problem with the AC controller in the car. Or possibly one of the pressure switches. I don’t know exactly how the circuit on that works. The 960 AC system is much more complicated than the 240 system. Your 960 also has a high pressure switch on the AC condenser.
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Old 07-25-2022, 04:56 PM   #7
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Sounds like you have figured the location of the accumulator - should be same spot as my older 740 - in the top right of the pic below. You can unplug the switch connector (probably a black 2 pole connector on yours) and jump the terminals in the harness plug with a paper clip to bypass the pressure switch. If the compressor clutch engages, at least you know it's functional. Don't leave the jumper in place beyond the short function test. You will then need to move on to checking the freon charge, pressure switches, control head, etc.

First step really would be to hook up the charging manifold & see if there is any freon in your system.

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Old 07-25-2022, 05:18 PM   #8
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sometimes when the clutch coil goes bad it can draw way more power than it's supposed too
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Old 07-25-2022, 05:57 PM   #9
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Quote:
Originally Posted by philski o'flood View Post
sometimes when the clutch coil goes bad it can draw way more power than it's supposed too
is there a way I can check that with a DMM? Where is it located?
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Old 07-25-2022, 07:32 PM   #10
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Quote:
Originally Posted by mschultz373 View Post
is there a way I can check that with a DMM? Where is it located?
The clutch coil is the electro magnet that the pulley is attached too. When it is energized, it pulls in the outer spring plate that you can see (not moving), and connects the pulley to drive the compressor. The pulley is freewheeling in your pic, not connected to the compressor (via the coil & outer plate). If you jumper the accumulator switch & the coil engages without issue, then you will know it's not the coil or compressor at issue, as I said.

Last edited by lookforjoe; 07-25-2022 at 07:43 PM..
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Old 07-25-2022, 08:07 PM   #11
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jumping the switch at the accumulator doesn't engage the clutch.

however, connecting and measuring the amperage across the AC clutch fuse holder reads at 118mA. The clutch would engage and disengage as I made the connection.
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Old 07-25-2022, 10:07 PM   #12
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Quote:
Originally Posted by mschultz373 View Post
jumping the switch at the accumulator doesn't engage the clutch.

however, connecting and measuring the amperage across the AC clutch fuse holder reads at 118mA. The clutch would engage and disengage as I made the connection.
OK, so if manually interacting with the clutch coil feed causes the clutch to engage, then it is unlikely that either the coil or the spring plate are at issue. so, you need to get the system tested in terms of circuit wiring, freon leakage, etc.

As a short cut you can always buy one of those R134a cans with a fill hose/gauge & try adding some freon to see if the AC then works. That will let you know if you have a refrigerant leak without spending $$$ for a system test up front... You need to pay attention to the gauge for pressure / temp
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Old 07-25-2022, 11:10 PM   #13
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What year 960 is it? The compressor clutch on newer 960s (1995+?) is controlled by the ECU directly using a separate linear pressure sensor and a dedicated fuse/relay. On late 960s the climate control unit has no direct control over the compressor and only requests the ECU to turn it on with a ground signal through the accumulator low pressure switch. If it's newer then the only way the clutch fuse would blow is if the clutch wire is shorting to ground somewhere or the clutch itself is drawing too much current. Early 960s have the clutch controlled by the climate control unit so it could be an issue with the climate control unit itself or its wiring
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Old 07-25-2022, 11:47 PM   #14
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who and/or what in the world is your avatar?

Mine is Lee Van Cleef, the actor famous for his Western movie works, but as an American ninja in an early 80s TV series called The Master.

Ok I added the mask during Covid lock down and I don't look a thing like the guy pictured.

When my coil went bad the volt gauge would zap down into the red as soon I hit the AC button and blow the fuse.

I put a 25A in there and that held for a bit until I swapped out the coil.
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Old 07-26-2022, 12:01 AM   #15
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Quote:
Originally Posted by mschultz373 View Post
the AC clutch fuse holder reads at 118mA.
is that enough to pop the fuse? that like a tenth of an Amp right?
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Old 07-26-2022, 12:05 AM   #16
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you need to measure the coil resistance and compare to what specs say it should be. I think most of the time they fail open and draw too much popping the fuse
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Old 07-26-2022, 12:36 AM   #17
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The first thing I do is connect the machine and suck it down and see how empty the system is.

Then charge it back up and see what happens.

Btw The compressor isn't gonna kick on if the system is really low on pressure.
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Old 07-26-2022, 01:35 AM   #18
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Get you one of these and test the draw on the clutch.
https://www.harborfreight.com/30-amp...ter-67724.html
Sounds like you have a bad clutch.
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Old 07-31-2022, 11:59 PM   #19
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Quote:
Originally Posted by kyote View Post
Get you one of these and test the draw on the clutch.
https://www.harborfreight.com/30-amp...ter-67724.html
Sounds like you have a bad clutch.
I do need one of these. I am idiot - my DMM only measures up to 10A for 30secs. So no way to know what the actual current draw across the AC Clutch is. but - it keeps blowing 15A fuses, so clearly something is eating more power than intended.
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Old 08-01-2022, 03:53 PM   #20
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set your DMM to ohms and measure the coil resistance
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Old 08-01-2022, 04:31 PM   #21
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Quote:
Originally Posted by philski o'flood View Post
you need to measure the coil resistance and compare to what specs say it should be. I think most of the time they fail open and draw too much popping the fuse
Quote:
Originally Posted by philski o'flood View Post
set your DMM to ohms and measure the coil resistance
sorry, didnt' mean to miss this. again, hate to be the n00b, but how do I measure resistance at the coil? i don't figure I can measure ohms across the fuse block, like measuring the amperage.
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Old 08-01-2022, 08:02 PM   #22
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there is only one wire on the compressor
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Old 08-02-2022, 12:47 PM   #23
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Quote:
Originally Posted by philski o'flood View Post
there is only one wire on the compressor
So you disconnect the coil wire and measure resistance from that one wire to a nearby ground (compressor body perhaps)?
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Old 08-02-2022, 01:22 PM   #24
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Quote:
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So you disconnect the coil wire and measure resistance from that one wire to a nearby ground (compressor body perhaps)?
Exactly. Compressor connector to compressor case.
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Old 08-02-2022, 02:08 PM   #25
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it takes two to tango
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