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Showing content with the highest reputation on 04/20/2023 in all areas

  1. I would guess the system is working as expected since actual on car testing is so similar. To an old school guy like me, it does appear very different than the way heater fans worked in the past. It seems the voltage split of 1.5 volts from low to high speed is pretty narrow and high speed is a full four volts or so below nominal system voltage, so the maximum speed possible would be wildly different. I don't see much of anything in the FSM that contradicts the present operating parameters? Have any probes been done of input voltage with the blower under load and operating? It seems counterintuitive that voltage would be higher under load but is it possible the system limits open circuit voltage for some reason?? Lack of feedback connection?
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  2. Ronnie, I thank you for your advice. That looks to be the best way to go. Thanks again for all your assistance!
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  3. Go to a salvage yard and get a good used one. Most of the big GM cars of that time period with auto HVAC controls used the same module so they should be plentiful and cheap. If that fixes the problem send the new one back.
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  4. I hesitate to suggest much in this area as I do not have an 89 FSM, but a scan of my 1990 FSM suggests checking the control module red/black (2B) input wire for full battery voltage. It is fed by a fusible link which is hot at all times. I don't find a specified output voltage for high speed in the FSM, but there is an orange feedback connection between the purple blower motor wire and terminal "P" of the programmer which is under the right side of the dash. I would guess that is where the programmer determines if commanded voltage is equal to actual voltage. It also says the command from the programmer to the blower module is a variable voltage. I do not know if there is a blower fan override or output control in the BCM diagnostics or not. Some functionality is different between the touch screen cars and the non. The BCM is the master controller here. In my FSM, only two conditions have a diagnostic tree: high speed fan only, or no fan operation at all 😖
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