Labrat

'91 AC intermittent problem

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I had my AC system replaced last year but kept everything R12.   A few weeks ago the Compressor didn't appear to be working  for a few days then for whatever reason everything was good again.  Yesterday same thing happened.   All the buttons and lights are functioning on the dash control system so I think that is OK.  Any ideas where to tell my mechanic to check next.  I do have the factory manual to help him.  Thanks.

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This switch is for 88-90 only.  Did '91 change something so it isn't needed?  I can't find one listed at various Auto Retail sites.

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As additional information, I have no problem lights on the instrument panel telling me to "service Ac soon" or even that I have a problem.  Would there be a problem code in  the system if I have it scanned at AutoZone?

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3 hours ago, Labrat said:

Would there be a problem code in  the system if I have it scanned at AutoZone?

 

They might be able to. You can check the switch DIY. Engine running- enter OBD, ECM INPUTS, EI78 and with AC on MAX COOL turn the wheel. The switch should go from LO to HI and the compressor will kick out- if the switch is OK.

 

4 hours ago, Labrat said:

This switch is for 88-90 only.  Did '91 change something so it isn't needed?  I can't find one listed at various Auto Retail sites.

 

Yes, sorry I didn't catch that. That IS squirrely- ANOTHER "running change" with production?

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Well I'd look at BD-28 (low AC pressure sensor). If it drops below zero the AC will turn off

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Check rpm gauge. AC compressor will not engage if the rpm gauge in the IPC is reading zero rpms with engine running. On mine I had intermittent electrical problem with ECM, that made rpm gauge read normally one minute when the engine was running, and then the next minute it went to zero rpm even though the engine was running. When the gauge went to zero rpm, the compressor would disengage. I posted about this but apparently nobody else ever observed it or made the connection, but I guarantee it is a real fact of correlation between rpm gauge on IPC display and whether or not AC compressor runs The fix for me was to replace ECM.

Edited by ChrisWhewell (see edit history)

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Well, after checking everything it was the simplest failure.  The electrical connection at the compressor is loose.  I'll cut off the plug-in and replace it today.  Thanks for the help Forum.

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