Question about 1991 Chevrolet S-10

6 Answers

Heater/AC control non-functional

1991 Chevy C1500 P/U; the digital heater/AC control failed gradually, first acting strangely, resetting, then going completely dead, not even LCDs lighting up. I've tried two used controllers, one labeled as ''tested'' with the same results. Because of the $380 price of a new control, I'm reluctant to purchase until I'm certain it's not something else. I have 12VDC and ground in the plug and 8.5VCD (strangely) also. The Haynes manual shows 5VDC on a Tan wire; the only tan wire has 0 VDC. I'm not confident about the Haynes manual wiring diagram. That's where I am now.

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  • dhamos Feb 23, 2009

    1991 Chevy C1500 P/U; the digital heater/AC control failed gradually, first acting strangely, resetting, then going completely dead, not even LCDs lighting up. I've tried two used controllers, one labeled as ''tested'' with the same results. Because of the $380 price of a new control, I'm reluctant to purchase until I'm certain it's not something else. I have 12VDC and ground in the plug and 8.5VCD (strangely) also. The Haynes manual shows 5VDC on a Tan wire; the only tan wire has 0 VDC. I'm not confident about the Haynes manual wiring diagram. Who can confirm this wiring diagram? Where does the 5VDC come from? WHere is the other end of the tan wire?That's where I am now.

  • dhamos Feb 23, 2009

    1991 Chevy C1500 pickup.
    The heater controller is dead. I have tried two other used units with the same result. Does anyone have a factory wiring diagram? Does it show that 5VDC should be on the tan wire? Please look to see where that tan wire gets 5VDC and let me know. Thanks

  • dhamos Feb 24, 2009

    While you state that the tan wire is the fan speed, you haven't said where that info comes from. Again, the Haynes manual says the tan wire is +5VDC; the connection reads 0VDC. If you have a real chevy wiring diagram for the 91 C1500 P/U, that will show, over several pages, where the tan wire leads. You can't trace it under the dash easily if at all. I could have purchased a wiring diagram on-line, thought I'd try you folks first. Does anyone have one? The tan wire terminates in the heat/AC controller. Where does it start? Is the tan wire really +5VDC according to the factory service manual for the truck?

  • dhamos Feb 25, 2009

    Up to this point the feedback I am getting is poor. Let's revisit: what I could really use is someone who has a wiring diagram for a 1991 Chevy C1500 pickup. The heat/AC digital controller in the cab has gone blank, I cannot control the heat, turn on the fan, etc. Two used digital controllers, when installed, exhibited the same symptoms. I feel pretty sure the problem is not the controller, but something outside the controller. I have a Haynes manual wiring diagram that indicates +5VDC on the "tan" wire in the connector. There is no voltage. If there is really supposed to be +5VDC on the "tan" wire and its not there, that would explain the symptoms. I am asking this: do any of you have a wiring diagram from a 1991 chevy C1500 shop manual that can confirm that the "tan" wire should have +5VDC and then also trace that wire back to the source of the +5VDC by following the various wiring diagrams? Failing that, I'll need to find a wiring diagram elsewhere.

  • Anonymous Mar 15, 2014

    body control mod to heater controll

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6 Answers

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  • Master
  • 362 Answers

The tan wire should be the fan speed control, as you change the speed of the fan the voltage will increase. If it is at zero the programer is faulty or the fan speed is turned all the way down.

Posted on Feb 23, 2009

  • Jason Morris Feb 24, 2009



    This is for a 1994 model but it is the same for 1991 thru 1994.
    The tan wire runs from the control module to the High Blower relay then to the resistor.


    Let me know if this helps, I can trace it further.
    Lone99star

  • Jason Morris Feb 24, 2009

    Here is a link to the diagram.
    Look at scematic # 26.

    http://www.autozone.com/shopping/repairG...




    Lone99star

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Try checking behind the glove box...there is a connection that has a red wire and two green stripped wires....on my 91 the connector melted a little and broke the connection ...if this is so the heater control will work sometimes and not sometimes...or not at all...I just cut the connector off and reconnected the wires and everything works great.

Posted on Nov 05, 2013

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  • Chevrolet Master
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IT IS VERY POSSIBLE THE BLOWER SPEED CONTROL MODULE IS DEFECTIVE OR SHORTED, THIS WOULD CAUSE ALL KINDS OF STRANGE SYMPTOMS, THE TAN WIRE BEING DEAD LEADS ME TO THINK THIS IS THE PROBLEM.

Posted on Feb 25, 2009

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  • Master
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Locate the relay in the fuse box for the heating/ a/c sytem and replace it... that should fix the problem. the relay should be under the dashboard fuse panel although it could be located in the engine compartment fuse panel near the battery.

Robert

Posted on Feb 24, 2009

  • maxim9691 Nov 23, 2010

    Had the same problem as the person above, even the same year of Truck.
    After seeing his post about the Tan wire , figuring it must be the hot wire or one of them. I wired my tan control module wire to my ignition power wire that runs my radio which is the same rating as the brown wire. Now after nearly a year of troubleshooting without success my heater/AC works again !!!! YeeeeHaw ! , I came back to post this in case someone else is having the same problem.

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Just check out the other end of the wire to make it confirmed.also cjeck out other wirings are they getting cut in between or connected loose.

Posted on Feb 23, 2009

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  • Master
  • 547 Answers

Pick up at scrap yard most of the time you will get at 25% of the cost and replace

Posted on Feb 23, 2009

  • 2 more comments 
  • albert getty
    albert getty Feb 23, 2009

    you may want to look in to tan wire it sounds like the problem is tan wire not connected thank you for useing fixya please rate me

  • albert getty
    albert getty Feb 23, 2009

    the tan wire should have voltage in it trace it back end to end

  • albert getty
    albert getty Feb 23, 2009

    http://www.vintagewatercooleds.com/tech/... use this link I think this is the one you are looking 4 please rate me

  • albert getty
    albert getty Feb 23, 2009

    you have tested the wires to other controls and same no power in wire it's the wire it's self or conection please remove and rewire as per diagram thank you for useing fixya please take your time to rate me after wire is replaced and reconected

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If you dont have your 5v reference then no amount of modules is going to do you any good. Get a diagram trace your wire back and i'm betting you will find it fried to a crisp somewhere along the line, but make sure you check your fuses first. start simple and work into it. GOOD LUCK!!!

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