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C4 Cooling and Heating Systems

everything blows out the defroster (1/6)
 10/31/17 4:06pm
Tony B
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Massapequa, NY - USA

Vette(s):
1990 Dark Red Mettalic convertible


Joined: 10/29/2017
Posts: 10

no matter what mode I select on the A/C / heat control on my 1990 everything blows out the defroster. Is there a diverter that needs to be replaced?
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Re: everything blows out the defroster (2/6)
 10/31/17 9:57pm
Atchafalaya
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Atchafalaya Basin, LA - USA

Vette(s):
Black 1979 L-82 Black 1996 LT1 Black 1999 Coupe


Joined: 3/20/2009
Posts: 518

Tony B said: no matter what mode I select on the A/C / heat control on my 1990 everything blows out the defroster. Is there a diverter that needs to be replaced?

Check for vacuum lines for leaks, and the mech. that opens and closes the damper-doors that re-directs air from vent to defroster....it's free, and easy to check.
 
 
Similar to this (but on your car):
 
 
 
Re: everything blows out the defroster (3/6)
 11/1/17 11:55am
Busterbrown
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Sonomma, CA - USA

Vette(s):
1995 coupe DRM


Joined: 11/4/2013
Posts: 14

Remove the pass side fuel rail cover. There is a vacuum valve that may have deteriorated?
Re: everything blows out the defroster (4/6)
 11/1/17 1:23pm
tloftus3
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Virginia Beach, VA - USA

Vette(s):
1996 Corvette Conv


Joined: 2/11/2016
Posts: 1

My 96 did the same thing, I had to remove the air control module which is located under the dash above the gas pedal.  I removed the box and found that the lines ran through a black rubber which had nipples which collapse after time.  I purchased new lines and removed that black rubber piece totally and joined the new lines to the control module.  After doing this my air blows out the vents on the dash when needed and the floor for heat.  I was informed on another forum that the default setting is defroster.  Mine works like a champ.  Good luck it was a b>>>>h standing on my head and removing the unit from under the dash. 
Re: everything blows out the defroster (5/6)
 11/1/17 6:08pm
Tony B
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Massapequa, NY - USA

Vette(s):
1990 Dark Red Mettalic convertible


Joined: 10/29/2017
Posts: 10

Ok, thanks!!
Re: everything blows out the defroster (6/6)
 11/2/17 1:29am
Phat98
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Crystal Springs, MS - USA

Vette(s):
1973 LS5 1981 Claret Red 1982 White 1985 Silver Metallic 1994 Torch Red Coupe LT1 1996 Dark Purple Metallic LT4 2001 Light Pewter 2003 Z06 2009 Atomic Orange


Joined: 7/29/2011
Posts: 23

tloftus3 said: My 96 did the same thing, I had to remove the air control module which is located under the dash above the gas pedal. I removed the box and found that the lines ran through a black rubber which had nipples which collapse after time. I purchased new lines and removed that black rubber piece totally and joined the new lines to the control module. After doing this my air blows out the vents on the dash when needed and the floor for heat. I was informed on another forum that the default setting is defroster. Mine works like a champ. Good luck it was a b>>>>h standing on my head and removing the unit from under the dash.


Correct on everything...defroster default is pretty much standard on most vehicles if there's an issue with the A/C system.

Also, spend 15-20 minutes to remove the drivers seat first, makes it much easier to recline and work under that dash.


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1973 Mille Miglia Red LS5
1981 Dark Claret Metallic
1982 White
94 Torch Red LT1
96 Dark Purple Metallic LT4
02 Black Convertible
03 Millennium Yellow Z06
09 Atomic Orange Z51