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Topic: Damp smell when interior fan is running on my 1991.

in Forum: C4 Cooling and Heating Systems

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Damp smell when interior fan is running on my 1991. (1/3)
 8/29/17 9:43am
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1991 C4 Corvette Quasar Blue coupe

Joined: 9/2/2013
Posts: 16

Does anyone know if there is a Cabin Air Filter in a 1991 C4, and a drain hose to drain any condensation inside the cabin evaporator case, and where they are. I have spent hours on line but have found nothing available, nor in my Haines repair manual. Any help would be appreciated.

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Re: Damp smell when interior fan is running on my 1991. (2/3)
 9/5/17 12:45pm
Black Shark
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Atchafalaya Basin, LA - USA

Black 1979 L-82 Black 1996 LT1 Black 1999 Coupe

Joined: 3/20/2009
Posts: 586

#1 ---Order a factory service manual for your make/model car.
(Haynes and Chilton's will only get you so far)
#2 --- Evap. case drain is on passenger side, underneath, below firewall.
#3 ---Hopefully not your situation; but, if the evap. case and/or evap. coil is dirty, it will always smell bad until they are cleaned.
You tube video of this fiasco:
Re: Damp smell when interior fan is running on my 1991. (3/3)
 9/5/17 9:58pm
Adams' Apple
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Duncanville, TX - USA

1985 Coupe-L98/Auto,Bright Red/Carmine. 1974 Coupe-L48/4speed, Medium Red Metallic/Black Deluxe.

Joined: 3/18/2009
Posts: 2183

No cabin air filter. Your smell is most likely mold forming on the A/C evaporator. Definitely check A/C condensate drain hose. You can possibly see it from the top, but it's easiest to get to it from underneath, if you reach up next to the exhaust pipe on the passenger side of the car(make sure the vehicle is COLD...don't want any heat tattoos).
GM has a TSB on odors from the A/C system. It involves cleaning the evaporator, and installing an "after-run" relay that will turn the blower motor fan on after the car sits for a few minutes after parking. The system DOES pretty much eliminate the odors, BUT....it also has a tendency to drain the battery eventually. I've disconnected plenty of those dang things to "fix" a parasitic battery drain that couldn't be found by normal diagnostic methods.
The cleaner used on the evaporator core, however, is good stuff. It normally comes with a long, flexible applicator to get down into the core to clean it. Check with your local GM dealer to see if they have it in stock...they should. The TSB covers ALL GM vehicles(except some Cadillacs, since they are factory equipped with the after-run relay) from 2016 back. Thumbs Up

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