A 93 940T. Everything was fine then 4 dash lights lit up: washer fluid, brake, parking brake and the battery. A moment later the AC stopped blowing cold (compressor disengaged). Washer fluid and brakes are all fine. I take battery lights more serious but am thinking the lamps could be a back feed from something else.

I found a similar situation on a 10yr old post from a general car site. Guy had his SRS light come on which in turn killed the AC. Blower works - just the compressor shuts off. He said that a couple weeks later while driving, the SRS lamp went off, and a moment later the AC came back on. Same issue - different dummy lights. The next day lamp was on, AC off, and thats where his posts ended.

From what I've read, this is a somewhat "common" problem, although I never heard of it. I noticed in the schematic that the D+ energizer wire at the alternator connects to the MCC controller, which might connect the battery lamp and the AC thing. I'm looking into common grounds, relays, feedback possibilities, etc. Belts, harmonic dampener, etc are all 3k from new NOS.

Any suggestions? TIA

When checking grounds, items mounted in plastic, such as lights have ground wires, and therefore grounding points. Items that only have a power wire going to them obtain their ground through contact with the engine or body.

On a car of your's age, you should consider unplugging wires, cleaning the contacts, adding dielectric grease and zip tying any that you can.

Bad connections can drive you crazy!

Do one connector each week - that way if you have a problem, you know where to look.

clean all the grounds

Same sugg I offered on TB. Fix the alt D+ output and the dash lights will go out. The AC will come back on.
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Art Benstein near Baltimore

Was ist Übergangswiderstand?

When I have an issue with a 1979 240, I'll let you know.