Constant Hot air out of vents? Help

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Michael Farrell

Not-quite-so-new-guy
Aug 4, 2016
25
1
8
Carleton Place, Ontario
Hi All,

finally got my car up and running but I'm noticing one issue, no matter where my temperature control is "hot" or cold, it blows hot air, Blower motor works on each speed and I can hear the vents open and close when I go from defrost to AC, but toggling between hot and cold I hear nothing which I find suspicious. where should I start for troubleshooting?
 

ck80

Moderator
Moderator
Supporting Member
Feb 18, 2014
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Hi All,

finally got my car up and running but I'm noticing one issue, no matter where my temperature control is "hot" or cold, it blows hot air, Blower motor works on each speed and I can hear the vents open and close when I go from defrost to AC, but toggling between hot and cold I hear nothing which I find suspicious. where should I start for troubleshooting?

I'd start with the air blend door and go from there. Easiest way to check is open the glovebox, empty it out, then press in the metal tab (typically on the driver side of the box assembly) that catches on the dash pad and let's the glove box door drop open all the way dowe towards the carpet.

Look up inside and you will see the cable leading from the climate slider to the pivoting arm that in turn operates the blend door.
 
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jlcustomz

G-Body Guru
Nov 22, 2011
983
1,097
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The heater valve inline on the heater hoses commonly freezes up, also lots of small vacuum hoses & the controller to go wrong & not operate it. You could also clamp a heater hose line to shut it as a test. Valve is cheap & easy but if controller issues are the problem some have put in a hardware store manual ball valve as a temporary or even permanent fix.
 

axisg

Comic Book Super Hero
Jul 17, 2007
2,684
2,356
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YYZ
like others have said, its either in the blend door or the heater control valve. AC cars still flow coolant thru the heater core ( for blend function ) in all settings other than MAX AC from what I understand. Every summer I put the valve on manifold vacuum to keep it closed, then put it back inline for the fall and spring. It's located inline on one of the heater hoses closer to the firewall with a vacuum line from the small vacuum ball mounted to the heater box. When they fail its often in the open position and inexpensive to replace

http://www.rockauto.com/en/catalog/...338,heat+&+air+conditioning,heater+valve,6860
 

Michael Farrell

Not-quite-so-new-guy
Aug 4, 2016
25
1
8
Carleton Place, Ontario
Hi Guys,
quick update, blend door cable is working from what I can tell, I cant seem to find a vacuum valve everyone mentioned if I follow my heater core lines back to the firewall I find what looks to be an electrically controlled valve running to my blower motor, also noticed my blower motor only functions on high would that affect anything?
 

Longroof79

Rocket Powered Basset Hound
Oct 14, 2008
12,191
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Gainesville, Fl
The heater valve is usually positioned on the right side of the intake manifold...at least on a Chevy small block it is. I agree that the problem might be the heater valve, especially if the blend doors are working properly.
 

Opie Knievel

Rum Fueled Midnight Mechanic and Moderator
Sep 6, 2010
1,512
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Brodhead, Kentucky
If your blower only works on high, there's a good chance that your blower resister is bad or possibly the fan speed switch.
 
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