drwatson32.exe Posted April 10, 2023 Share Posted April 10, 2023 Hello there! My dad just picked up a '91 where the previous owner ran a toggle switch into the interior and I took at look to help figure out what's going on. It looks like the switch was added to intercept power from the blower motor, so I thought it stood to reason that it was because of a failed blower control module. Next, I lurked forums to confirm whether that's the case. It seems the consensus is that these modules tend to fail such that the blower runs at full power. This blower will run at various speeds as set from the controls, but I'm seeing ~1.6v on the purple wire with the ignition switch in the off position. While I mended the original harness connector and pulled out the rigged wiring, that presence of voltage sounds like a parasitic drain, so we left the motor disconnected for now. Can anyone confirm that there should be 0v at the connector when the car is off? (There's just a lingering doubt in the back of my mind, in case there's some sort of digital logic here that I'm not hip to.) Thanks! Link to comment Share on other sites More sharing options...
EmTee Posted April 10, 2023 Share Posted April 10, 2023 Yes, blower control module is failing. Just ordered one for my wife's '93 Allante' which runs full-speed with the key OFF... I ordered an offshore replacement on Ebay. Link to comment Share on other sites More sharing options...
2seater Posted April 10, 2023 Share Posted April 10, 2023 The most common way the blower module fails is, it won't shut off and runs with ignition off. Unless the 91 is different than a 90, the module receives power through a fusible link and is always live. The purple wire is the output to the blower motor but there is also a connection to the HVAC programmer which the wiring diagram calls a feedback input (orange wire). I can't say for certain that is a draw but I suspect what you read may be normal. One way to check for an abnormal parasitic draw is to place an ammeter between the battery terminal and the battery cable. Some draw is normal. Link to comment Share on other sites More sharing options...
padgett Posted April 10, 2023 Share Posted April 10, 2023 GM says normal draw with everything off is 50 ma. Mine usually draw 20-30ma. The blower control module has a SCR that usually fails short but sometimes open. Was used by all GM cars of the period with ATC. I keep a spare around. 2 Link to comment Share on other sites More sharing options...
Barney Eaton Posted April 10, 2023 Share Posted April 10, 2023 GM used that controller on cars with "automatic" HVAC for several years. They are about $80 new......but there should be plenty in the pick-n-pull Looks like the attached photo.... the heat sink is inside the HVAC ductwork. 1 Link to comment Share on other sites More sharing options...
drwatson32.exe Posted April 10, 2023 Author Share Posted April 10, 2023 Thanks for the replies! Still not sure on whether there should be any voltage present at the fan, but it sounds good to just grab a couple modules from the junkyard and compare before springing for a new one. Thanks again. Link to comment Share on other sites More sharing options...
2seater Posted April 11, 2023 Share Posted April 11, 2023 Connect a flashlight bulb across that 1.5v and see if there is actually any current flow there. Link to comment Share on other sites More sharing options...
padgett Posted April 12, 2023 Share Posted April 12, 2023 and if the bulb blows you have more. 1 Link to comment Share on other sites More sharing options...
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