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Old 10-09-2017, 07:15 PM   #1
oifish
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Default New A/C compressor clutch won't engage

Car is my brother's 91 745 NA. His old R12 system had leaks and the compressor recently seized up so it was time for replacement.

We installed all new components (besides evaporator) including the proper amount of oil for the compressor. Pulled a solid vacuum that held overnight. But when trying to charge the system, the new clutch won't engage. I tried jumping the connection at the pressostat, but nothing.

His old a/c compressor was only a single wire with a weird little box that was mounted at one of the bolts to the compressor and then on to the red/green wire. The new one has a black wire from the clutch and a green wire the y's into the harness, then connects to the red/green wire.

We're stumped on why it won't engage. The idle's raise after about 10 seconds and we did double check the fuse.
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Old 10-09-2017, 08:19 PM   #2
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Break out the test light. Did you forget the ground wire?
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Old 10-09-2017, 10:14 PM   #3
DET17
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Quote:
Originally Posted by To old for this View Post
Break out the test light. Did you forget the ground wire?
This. Check your ground from the compressor body directly to the battery post.... if not essentially zero ohms, run a ground wire to the frame rail, right behind the battery (existing tap points).

When I bought my 92, the JAPAN made control circuit board (attached to the back of the HV control knobs) had a failed circuit.... fairly common. Once you've confirmed ground, then see if that single wire has got 12V on it when the AC is engaged.
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Old 10-09-2017, 10:40 PM   #4
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Derp, forgot the accessories are isolated. Grounded it and no problems
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