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The following write-up by David Beierl is in response to an article posted by GoWesty's Lucas Valdes. The original article can be found posted herein.
Hullo Lucas --
From your fine article on Vanagon cooling fans:
There is nothing in the wiring diagram that would indicate that the AC system can operate the radiator fan at any speed other that the first stage. However, my experience with my own 87 Westy with factory AC is that, on a super hot day charging up a long grade at 80 MPH with my 2.4 liter engine and AC blasting, I have heard the third-stage fan speed come on when I KNOW FOR SURE the temperature on the gage is nowhere near 7/8’s. I know that AC is involved because it I can feel the compressor shut-down while the turbo speed fan is on. Furthermore, it WILL NOT do this with the AC off. So, maybe someone smarter than I can have a look at the AC schematic and figure this one out.
Take a look at Bentley 97.140/141 -- mine shows the stage-1 driven by thermoswitch at track 19 going to 21, and also by the A/C relay terminal 5/6 (track 12) whenever the A/C is on.
Stage-3 is by thermoswitch and relay at track 18, which as you say shuts off the A/C compressor through the relay at track 17.
But have a look at track 14 -- the A/C overpressure switch dives up into the panel and drives the *second*-stage relay at track 23 to bring the refrigerant pressure down. I don't know the resistor values but presumably second-stage is noticeably faster than first-stage while still something short of artificial-hurricane.
As to it shutting down the compressor, I have three thoughts, first one is that old debbil coincidence. I remember spending many hours with my '39-era Hammarlund shortwave receiver, tuning back and forth chasing the signal fade from European broadcasters. I was somewhat dismayed years later to learn that my efforts had done exactly squat, and I'd been fooled by the cyclic nature of the fade itself. Not saying this is the case, but to bear in mind. Second is that maybe the extra heat shed from the condenser is heating up the thermoswitch somehow and triggering the actual stage-3 fan. Third is maybe the wiring in your vehicle doesn't precisely conform to Bentley -- maybe the overpressure switch is driving stage-3 instead of stage-2, for example.
Regds,
david
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David Beierl - Providence RI USA --
http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage," '85 GL "Poor Relation"
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