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Ever since I had a dead battery (car sat 2 weeks while I replaced the head gasket) the fan has been acting nuts - it was obviously on low voltage turning on/off when I hooked it back up, so I got a brand new battery, but the problem didn't change:
The fan speed seems to be stuck on either end of the scale, blowing almost full force, but increasing and decreasing just slightly in response to the fan speed controls, which show normal display bars from 1-9. Then when I hit the brakes (not always!) or do other things that draw current, it will sometimes fly up and down in a random pattern. The other times it will run at speed 1, then marginalize that by the scale also, like the baseline won't set correctly.
I have tested and it does seem to be purely electrically influenced as it does this sitting still (so not mechanical connection problem) and I thought it was stone dead, but I can feel the very slow air coming out at standstill so I know it's not.
I checked the wiring connection at the ACC unit and no effect playing with it or connecting etc. I removed the fan speed controller, and after seeing the dark board was convinced the MOSFET chip had gone bad and the P/N junctions were leaking current depending on the voltage sourced, so I got a couple of exact replacements and soldered one in - no change in operation whatsoever. I haven't tested the smaller chip on there (or the one on the back) but all the resistors and caps look fine... I need a break out box to test that ACC and see if the output from the unit is what it is supposed to be, regardless of what it says, or another unit that I can test to see if it's just plain bad -
The only grounds I ever took off were the 2 engine on the intake manifold when I did the head gasket swap, and I don't see how it would cause the ACC fan speed to act up and nothing else.
Any experts out there thing my fan speed controller IS bad, or the ACC unit? I'd like to get some used ones to test out -
If it turns out that Mosfet is the source of problems for people on this board when the fan just goes completely dead, I can fix them for 20 bucks instead of buying a new one, but would need a dead unit to test the theory on -
anyone want to send me a dead unit?
posted by 68.91.1...
, Fri, 23 Jan 2009 17:18:30
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