Question about 1990 GMC Sierra

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Heater controls for my 1990 gmc pick up do not work. Could it be the inline fuse? If so where is it? I checked the heater/ac fuse and it is good. I had disconnceted the battery and when I reconnected it the controls were not working nor did they light up. Just prior to disconnecting the battery every thing worked fine.

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  • John Luppino Dec 30, 2010

    There is not a fuse box under the hood. I also checked the other fuses in the fuse box all are good

  • John Luppino Dec 30, 2010

    the blower motor is blowing at low speed on it's own I have on control of it the control pnl is blank. Nothing on the panel works on/off, fan speed,select button,tempature. The panel is blank. I was reading the owners manual and it said there is an inline fuse but it does not tell you where it is. Also my truck is a 1990. Does it have the same wire diagram as the 1999?

  • John Luppino Dec 31, 2010

    This sounds more like the problem. Not what I wanted to hear (hoping it was a fuse). I was in the process of looking for a used one for troubleshooting. With that said can you tell me where the inline fuse is anyway? I expect for my son to hold on to this truck for a couple more years I just put a rebuilt motor in a month ago.

  • John Luppino Jan 01, 2011

    GGood job but no one has told me where the inline fuse is!!!!!the problem wasfixed by unplugging the control panel and pluging it back in.
    O.

  • John Luppino Jan 01, 2011

    problem fixed. I unplugged the control panel waited @ 20 min thenplugged it back in andit worked

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Generally these controls go bad and nothing works. They are an imported item GM uses of course. The electronics short circuit and go completely dead. Best to find a used one that works for new ones are expensive

Posted on Dec 31, 2010

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Hi and welcome to FixYa!

I'm suspecting that you have a faulty pcm (powertrain control module). The PCM has connectivity on all electrical current that runs inside the car including the engine, transmission, internal accessories, lights, etc. If the PCM is faulty something will surely fail.

I strongly suggest that you replace the PCM to resolve the problem.

Hope this helps and thank you for using FixYa! Happy New Year!

Posted on Jan 01, 2011

  • brisigler1 Jan 09, 2011

    Can you explain better what the PCM is and where to find it on the truck?

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This trucks had common problem of the blower motor resistor going bad or burning out and it would only work on high speed. The resistor is located under the passenger side dash by the blower motor.

Also, I suggtes check the wiring diagrams for any blow/fried connections...

heater controls for my 1990 gmc pick up do not - zjlimited_369.jpg

Fig. Heater Blower Controls Schematics (1999)

zjlimited_370.jpg

Fig. Cell 60: Front HVAC Blower Motor(c) (1999)


Hope this helps; keep us updated

Posted on Dec 30, 2010

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My Chevy truck has fuses for the heater in both the dash fuse panel and the engine compartment fuse panel. Maybe yours does too. Mine's newer than yours though and may be different.
Also being that it's the control panel that's not lighting up, it could be a fuse that involves the dashboard control panel rather than the heater/ac fuse.

Posted on Dec 29, 2010

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