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I searched.... read dozens and dozens of posts...

2 questions I haven't been able to conclusively answer:

  • Where exactly is the oil pressure switch relating to HVAC function?
  • Is there a fuse or something in the resistor pack that would stop the fan from blowing at ANY speed (incl no high speed) ?



Also, does anyone have a photo of the 2 relays under the dash? I was only able to find one relay under there.... but there are like 15+ unused or disconnected wire harness connectors dangling around various parts of the dash... no way to know which ones are for options my truck never had and which ones are actually disconnected and should have something on 'em

Thanks!

(BTW I can at least eliminate the possibility that the relay behind the left headlight is bad.... THAT one was easy to isolate and test... 80 ohms across trigger, trigger clicks, and continuity on switched contacts when it is triggered.)


It's the same oil pressure switch that controls the fuel pressure back-up relay, the one mounted right next to the filter. I don't know why GM did this, it's weird. It prevents you from running the blower if the engine is off, even if the key is in the ACC position. There is a TSB on this, as the original ETM/Service manual had it wrong in the wiring diagrams. If you have the Alldata CD, it's in there. SB90-04-007 "A/C Compressor - Wiring Circuit, Manual Correction".

Glad you got yours working. The problem I had is that my original oil pressure switch was leaking through the connector. Even after I replaced it, my blower was still flaky. I cleaned the contacts on the switch and connector and voila! It works fine now. The blower is a bit weak though.

Last edited by armyBob; 05/27/07 02:51 PM.
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