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1991 GMC K1500 Cannot Adjust Heat


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New User

Nov 28, 2014, 1:48 PM

Post #1 of 9 (2772 views)
1991 GMC K1500 Cannot Adjust Heat Sign In

I may have multiple problems. I cannot adjust my heat. Hot air is always blowing. When I push the heat control button to low or high, all the arrows will light up, flash continuously and then just go out. The fan works and the other switches for adjusting face to feet work. I hear the clicking in the dash or control unit, whichever. I replaced AC control unit per GMC and that didn't fix the problem. Now here is problem 2, my temp. display has been flakey, meaning it will show over heating then nothing then normal then over heating etc. Now the temp. display doesn't move off cold and now my heater only blows cold air. GMC told me to replace the instrument cluster but since the AC control unit wasn't the problem, I'm reluctant to buy another cluster.


loin_lord
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Nov 28, 2014, 2:59 PM

Post #2 of 9 (2753 views)
Re: 1991 GMC K1500 Cannot Adjust Heat Sign In

Did the change in behavior of the temp display and only blowing hot or cold air coincide with any sudden changes in the outside air temp?


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New User

Nov 28, 2014, 3:09 PM

Post #3 of 9 (2751 views)
Re: 1991 GMC K1500 Cannot Adjust Heat Sign In

No, the temp. gauge fluxuated for about a month with hot air flowing even with the heater turned off. It wasn't until the gauge quit totally that it started to flow cold.
Fyi, I did change the thermostat also, and there was no change.


Discretesignals
Ultimate Carjunky / Moderator
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Nov 28, 2014, 5:29 PM

Post #4 of 9 (2742 views)
Re: 1991 GMC K1500 Cannot Adjust Heat Sign In


Quote
When I push the heat control button to low or high, all the arrows will light up, flash continuously and then just go out.


That means there is a malfunction with the heater blend door actuator or its circuit. The clicking in the dash might be the actuator with stripped gearing or a problem with the blend door linkage.

You mean your coolant temperature gauge is acting strange? You should monitor the voltage on the temperature gauge sender circuit while the gauge is acting weird to determine if you have a sender, sender circuit, or instrument cluster problem.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Nov 28, 2014, 5:30 PM)


Hammer Time
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Nov 28, 2014, 5:44 PM

Post #5 of 9 (2738 views)
Re: 1991 GMC K1500 Cannot Adjust Heat Sign In


Quote
No, the temp. gauge fluxuated for about a month with hot air flowing even with the heater turned off. It wasn't until the gauge quit totally that it started to flow cold.


That is sounding like you have more than one problem. This symptom is sounding like there is air in the system, probably resulting from coolant loss somewhere. Don't keep driving it until you get to the bottom of that symptom.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



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New User

Nov 28, 2014, 6:24 PM

Post #6 of 9 (2735 views)
Re: 1991 GMC K1500 Cannot Adjust Heat Sign In

where is the actuator and the blend door linkage located? Is it possible that is might be the actuator motor? The clicking sounds like its coming from the heater control head.
GMC shop said that the temp. sensor tested good. ( that's the sensor with 1 wire )?? I replaced the other sensor with 2 wires, ( I think that's the sensor to the computer )??
My coolant level is fine and always has been.


Hammer Time
Ultimate Carjunky / Moderator
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Nov 28, 2014, 6:32 PM

Post #7 of 9 (2732 views)
Re: 1991 GMC K1500 Cannot Adjust Heat Sign In

It's number 61 in the picture.



This actuator has no relationship with your temp gauge. The only thing that no heat coupled an erratic temp gauge indicate is air in the system, although I think you do also have an actuator or door problem.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Nov 28, 2014, 6:32 PM)


buffer
New User

Nov 28, 2014, 7:00 PM

Post #8 of 9 (2724 views)
Re: 1991 GMC K1500 Cannot Adjust Heat Sign In

Ok so just to clairify, heater blend door actuator is #61, and that may be my cool to hot blinking display problem?


I will double check the air in the system.


Could GMC dealer mechanic be correct, it may be the instrument cluster that is causing problem with the temp. gauge.


Hammer Time
Ultimate Carjunky / Moderator
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Nov 28, 2014, 7:03 PM

Post #9 of 9 (2723 views)
Re: 1991 GMC K1500 Cannot Adjust Heat Sign In

Sure, it could be anything in that electrical circuit effecting the gauge but the fact that the gauge problem is coupled with losing heat simultaneously tends to point elsewhere.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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