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Topic: Heater blows cold

in Forum: C4 Cooling and Heating Systems


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Heater blows cold (1/7)
 1/14/22 3:47am
AFammo
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Joined: 9/30/2021
Posts: 5

     My 85 blows cold air, no matter what the slider position is in.  The unit is placed in heat mode and the car was warmed up to 195. I thought that maybe vent was wrong and went through the defroster, vents and floor with no heat what so ever. The fan worked great. Any insight would be great.

 

     The tachometer worked when I test drove the car. After I had it in the garage, (starting and shutting the engine off) the tach went from 1500 RPM to nothing.  

 

   

 

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Re: Heater blows cold (2/7)
 1/14/22 8:33am
Black Shark
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Vette(s):
Black 1979 L-82 Black 1996 LT1 Black 1999 Coupe


Joined: 3/20/2009
Posts: 598

If hot water is flowing thru heater core; inlet and outlet side will be hot.

The above determines if valve is working correctly and if core is NOT restricted.

 

Other diagnostics follow after this is determined.

Re: Heater blows cold (3/7)
 1/14/22 9:39am
pvantienen
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, - Canada

Vette(s):
1993 C4 - Red, 6spd


Joined: 9/25/2020
Posts: 1

If you aren't smelling anti-freeze inside or the windshield isn't fogging up, you probably have a stuck blender door which is quite common as well. 

 

 

Re: Heater blows cold (4/7)
 2/23/22 2:38am
AFammo
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   There was no smell of anti-freeze, but when I looked under the 3 floor mats on the passenger side, there was a puddle of water.

   I'll try and get the car to warm up and touch the inlet and outlet pipes. I heard most C4 owners just bypass the system, cause the car is used only in warm weather.

 

    Wish I checked the heater and floor mats when looking at the car and I wouldn't be in this mess. Hindsight is 20/20.

Re: Heater blows cold (5/7)
 2/23/22 8:50am
Black Shark
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Black 1979 L-82 Black 1996 LT1 Black 1999 Coupe


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Sometimes people purposely bypass the heater core because they know for a fact the core is leaking.

Re: Heater blows cold (6/7)
 3/8/22 12:10pm
RobertM
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Coppell, TX - USA

Vette(s):
1989 White with all Red interior My first Corvette


Joined: 9/24/2021
Posts: 3

Where is the blender door and how do I access it? 

Re: Heater blows cold (7/7)
 3/8/22 2:06pm
lkedmiston
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Williamsburg, PA - USA

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1989 coupe


Joined: 6/8/2019
Posts: 13

If it's electronic, a little electric box will push/pull the actuating rod.  If it's manual, your control cable will be attached to the rod.  Either way, it's mounted right on the outside of the heater core housing.  What usually happens is the 30 year old plastic clip that holds the actuating rod to the blend door inside just gives up.  If that rod has become disattached and is just flopping around inside the core housing, you will not be happy about what comes next!  It is possible to get the core housing open from under, you'll never get it back together properly without removing the entire dash.  (ask me how I know this)  We all know that a heater core came down the assembly line first, and then they built a Corvette around it!  Yep, it's a lot of work, and a lot of time, but it's actually not hard to do.  Since you'll have the whole car apart, heater cores are fairly cheap, and you won't want to do it again anytime soon!  This guy has the best videos I've found on doing it the right way.  (it's a little hard to watch because he has the camera attached to his head, but still the best I've found.  Good luck, and as another Larry has said on many occasions, "Git-R-Done!"

Part one: https://youtu.be/1buzyWFbvu4

Part two: https://youtu.be/sSgOWqo719A

Part three: https://youtu.be/Bp1yfBPpn8c

 

 






|UPDATED|3/8/2022 1:06:56 PM (AZT)|/UPDATED|
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