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Heater on while swithch is on cold

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Old 07-06-2018, 01:28 AM   #1  
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Heater on while swithch is on cold

Hello, i have an issue with the HAVC controles. I do not have A/C in my car. The blower sends warm air in the interior while the controls are on "vent" and "cold".
What can cause this? The controls? Or some electronic issue?
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Old 07-06-2018, 06:28 AM   #2  
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Re: Heater on while swithch is on cold

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Originally Posted by IROCK1987 View Post
Hello, i have an issue with the HAVC controles. I do not have A/C in my car. The blower sends warm air in the interior while the controls are on "vent" and "cold".
What can cause this? The controls? Or some electronic issue?
Hi IROC1987 ,

First , before I answer , I have a question for you . Was your IROC built without A/C , or has it been removed by some previous owner ?

I ask this because many of these "I'm gonna clean up the engine bay and get rid of the A/C cause it don't work anyway" removals generally involve some butchery that ends up rendering portions of the heater controls inoperative as well . There are no "electronic controls" in the system which , other than the blower motor itself , is actually ran by and controlled by engine (manifold) vacuum . The system is designed that a complete loss of vacuum to the control head causes a default operation of heater core always "on" (receiving hot engine coolant) and defrost always on , providing a measure of safety that no matter what fails in the controls you'll have warm air coming full time from the defroster vents to ensure a clear (non foggy) windshield . Now , if moving the controls does indeed change the air flow from floor to dash to defrost vents then the system is still receiving vacuum and it's possible it's the heater control valve itself that isn't receiving vacuum , remember it takes the application of vacuum to the heater control valve to turn it off . So some more questions arise ; is your heater control valve still in place under the hood ? And if so , is the hard plastic tubing still connected to the top of it ? If all that is visually intact the thing to do would be to attach a vacuum gauge to that hard plastic line and verify that with the heater control set to max. cool position there is actually vacuum being applied to the valve , with the engine running of course (to give it it's "off" command , no hot coolant flowing) . Is there vacuum present ? The valve is stuck open . Is there no vacuum present ? There is a malfunction causing that loss of controlling vacuum (broken/disconnected vacuum line anywhere between the vacuum tap at the manifold and the heater controls , or perhaps a malfunctioned control head not sending the vacuum to the valve would be your two prime suspects here) .

I hope I've given you some insight into how the system operates and some things to check to try to troubleshoot the problem because , yea , an always on heater can really suck on a hot day and roasting one's butt off is no way to enjoy driving any car , especially a car as cool as are third gens are .

Last edited by OrangeBird; 07-06-2018 at 06:33 AM.
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Old 07-06-2018, 09:57 AM   #3  
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Re: Heater on while swithch is on cold

Thanks for your reply! Thankfully my car was built without A/C. With your info I have some direction where to look so I will dig in to it. Thanks!
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Old 07-06-2018, 11:57 AM   #4  
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Re: Heater on while swithch is on cold

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Thanks for your reply! Thankfully my car was built without A/C. With your info I have some direction where to look so I will dig in to it. Thanks!
Your welcome and I'm happy to have been able to help . When you find out why it's always making heat post up your results , and if I can help you with any other info feel free to ask .
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Old 07-09-2018, 12:07 PM   #5  
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Re: Heater on while swithch is on cold

Is it really cold outside where you are? I can set my temp all the way cold on my car, but unless I switch on the a/c, it's going to blow hot until December or so...
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Old 07-09-2018, 12:38 PM   #6  
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Re: Heater on while swithch is on cold

Well,..... The 82-89 Non-AC cars didn't use vacuum to control air flow; those cars had a cable controlled ventilation system. (82-89 AC cars all used vacuum and ALL 90-92 Controllers were vacuum controlled. ) The 82-89 non-AC controller has 2 cables that control the "door flaps" inside the interior mounted heater core box.

NON-AC cars kinda' depended on the outside air VENTS under the dash on the driver and pass side. The pull-handle "VENT" controls mounted under the column would open one side vent &/or the other side to allow outside air to be forced thru them and into the car while driving. They pretty much did nothing to help air flow unless the car was moving.

You can check to be sure that the non-AC controllers' cables operate freely because it's possible a door flap might be stuck,... but unless it's winter your pretty much going to get warm/hot air from the blower.

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Old 07-11-2018, 04:20 AM   #7  
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Re: Heater on while swithch is on cold

Thank you! I will dive into it and post the results
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Old 07-11-2018, 07:41 AM   #8  
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Re: Heater on while swithch is on cold

Thank You for the correction John !

In the half dozen or so third gens I've been involved with , ALL had been factory equipped A/C cars , and I've never seen one built without A/C , which is the basis for my mistaken notion that all of our third gens climate control was vacuum controlled . I had thought GM left the mechanical cable setups back in the second gen , and I really appreciate you setting the record straight with my (obviously) limited knowledge of the non A/C cars
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Old 07-11-2018, 09:48 AM   #9  
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Re: Heater on while swithch is on cold

No Sweat ! Each of us only knows what we know till we learn otherwise. Sharing our knowledge is what this place is all about and I too am constantly learning 'on the fly'. Heck; I for years I thought ALL non-AC thirdgens were cabled controlled till I finally bought an AC Delete 91 RS to part out; talk about being surprised !

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Old 07-11-2018, 10:03 AM   #10  
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Re: Heater on while swithch is on cold

It is , It's amazing how many variations these cars can present , and I do really appreciate your sharing you knowledge with me . My god , just look at the differences between say , an 82 base model VS one of your beloved later model Berlinettas and it's almost like it's an entirely different car !

I can just imagine the parts confusion so may different variants must have given folks over the years , give the parts man your exact submodel or the parts could look like they came from a whole different model line
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Old 07-16-2018, 06:05 PM   #11  
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Re: Heater on while swithch is on cold

My non-a/c 87 was stuck, the lever (and thus cable) moved a bit but jammed up. It wasn't until I fully pulled the dash out of the car that I learned why. A lighter was jammed in the heater box, jamming the door. Also found a razor blade down there... Sort of makes you wonder!

My "vents" were jammed solid, I thought those handles were for looks, but I got those freely moving when I pulled it all apart too.
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