I read with interest yesterday's posting on a similar problem. I have an 87 with no fan operation in any mode. I used the GM electrical diagnosis manual to try to figure out what the problem is. The results are confusing - and I'm no electrical wizard.

So far I have confined tests to the underhood area. All fuses are fine, fusible link is good. Grounds are fine and no broken wires that I can find.

The input from the controller to the blower control module (BCM) should be between 1 - 5 volts (according to the manual) but reads 10 volts. This reading stays constant no matter what the manual fan setting is.

There is a splice between the BCM and the blower that goes the the contoller. it appears to be feeding 1.4 volts to the blower regardless of manual fan settings (should be .5 - 5 volts). I expected that this wire would take a signal back to the controller - not from it.

The BCM provides no voltage to the blower at all. Blower works if I feed it 12 volts.

I guess this means that the BCM is toast. Would the fried BCM affect readings from the controller? I'd rather not pull it out if I don't have to. Does the 10 volts output from the controller signal a serious problem there or is possible that cleaning would help?

Thanks.