I have the same exact problem. Does any have any idea how to get around this. I have noticed that there are two vents on either side of the center console near the front. No air comes out of these when the A/C or fan is off, but when you drive down the road air starts to come out of them and increases with vehicle speed. The air itself only seems moderately warm, but its as if it pulls the radiant heat from the firewall right into your legs, and as hot air rises it eventually fills the cabin. I also notice that with the A/C on the air coming out from the same vents is cold. I should mention I have an 89 RS, but I've noticed the same ducts in an 88 Z28 as well. Does anyone have a clue as to how to solve this? One more thing, for those of you who have changed your own heater core: remember that flap or door near the heater core? It is actuated by the lower slide lever - the one that adjust from hot to cold.
Apparently GM used some sort of foam in an effort so seal the duct off from the heater core. Over time the material degrades and crumbles. I think this creates a gap that enables some of the radiant heat from the core to escape and come into the cabin. When the windows are down it creates a vacuum and pulls the air through the core even without the blower on. Does this make sense to anyone? I guess I could try to replace the foam but I'm not in a hurry to rip apart my whole dash and console again.

 

My car does the same thing. Anyone know why?

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82 Camaro:
350
Erson cam, ported heads,Comp Cams 1.6:1 rocker arms
Edelbrock Performer RPM intake, Holley 600
Crane Hi-6 ignition, Accel supercoil
TH350 tranny with 2500 stall.
Eibach Pro Kit
SLP 1 3/4" headers

 

???ANYONE???

 

Same thing here...only no a/c to cool it off! It really sucks when im in traffic and the fan (radiator) kicks on. I got a feeling we ALL have the same problem (kinda like the leaky t-tops). If anyone knows how this is fixed please help!
peace

 

I don't have this problem but I know what you are talking about. There is a way just to block up those vents if you wanted to but that wouldn't be too good. I know in my car when I have the system totally turned off air does come in through the lower vents. However the temperature of this air represents the temperature outside and not extra heated air. You could check to see if the motors that open and close the vents are all working. I would say the first thing to do it make sure there are no vaccum leaks and that the system in general is working first. The only thing I would think that could be the problem is air is being directed over the heater core then through the console vents. Whenever I have a problem like this I fiddle around with it. Well good luck guys.

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88 Camaro Sport Coupe
2.8L V6 173ci
K&N Air Filters
JET Underdrive Pulleys