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2002 Deville base
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29 Posts
Discussion Starter #1
The heat in my car only works when your going highway speeds (about 45 and above) when at idle or just cruising in town it blows almost freezing cold anyone know what can cause this? And this is with the ac turned off and heat cranked all the way to 90 degrees
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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70,380 Posts
Poor coolant flow through the heater core. Your heater core coolant flow is designed for full flow at all times; discharge air temp is controlled by blend doors in the HVAC stack. The heater core coolant supply/return lines should be HOT at all times.

Either you or a good radiator shop need to flush the heater core - if you have used ANY sort of sealants or "conditioners" it's very possible that the core is partially clogged. Otherwise, generally poor coolant flow overall, and you need to find out why.
 

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2002 Deville base
Joined
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29 Posts
Discussion Starter #3
Poor coolant flow through the heater core. Your heater core coolant flow is designed for full flow at all times; discharge air temp is controlled by blend doors in the HVAC stack. The heater core coolant supply/return lines should be HOT at all times.

Either you or a good radiator shop need to flush the heater core - if you have used ANY sort of sealants or "conditioners" it's very possible that the core is partially clogged. Otherwise, generally poor coolant flow overall, and you need to find out why.
would it be best to just do a coolant flush? i know with northstars you wanna keep up on that anyway
 

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Super Moderator
2010 DTS
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87,306 Posts
"Frezezing cold" sounds like the A/C is activated. I'm confused. Why would you even have the heat on at this time of the year? Are you in AUTO mode maybe?
 

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2002 Deville base
Joined
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29 Posts
Discussion Starter #5
"Frezezing cold" sounds like the A/C is activated. I'm confused. Why would you even have the heat on at this time of the year? Are you in AUTO mode maybe?
not on auto mode strictly heat, and im just trying to fix all the small things wrong with my car because it gets cold at night where i live. when i say freezing i don't mean ac cold its just no heat whatsoever.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,998 Posts
STEP #1 - ALWAYS - check for DTC's - Diagnostic Trouble Codes - using the on-board scanner -
if you don't know how - go here -

post any codes you have -
ALONG WITH THEIR DEFINITIONS -

include whether they are C-Current or H-History -

for code definitions - go here -


here is a how-to video -
 
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