Hot Air Leak at Back of Heater

Created: 5/30/98

Last updated: 8/29/99

Author/source: DML

From: Dave Swingle

To: dmcnews(AT)

Subject: re: Heater Control Valve

Date: Wednesday, May 27, 1998 10:04 AM

I have verified that the water valve is operational. It closes (pull-in) automatically with the A/C in Max, is open at all other times. The recirculator trapdoor on the A/C unit opens at the same time the water valve closes. The mode switch works well, and everything functions normally. For my test I simply put a tie-wrap around the arm on the control valve to hold it closed all the time. This very effectively shut off the hot water, but I'd rather do something a little more convenient, or even fix the real problem (Maybe an air leak where the tubes come thru the front firewall?)

Thanks for the help...


Subject: Re: Heater


Your description of a possible air leak at the fire wall is very close to the problem. There is, for no reason that I can see, a hole in the air box, refereed as the

"Case" in the workshop parts book (7:1:1) item 16.

This opening is covered by a piece of foam, refereed to as a "Tube Seal" item # 19.

(The illustration in the manual is incorrect and does not show this seal in the correct location) On many cars the glue has dried out and the foam, becomes partially detached, this condition forces air to by pass the condenser and heater core. The result is hot air at the drivers foot well in summer and cold air in the winter. To repair this you need long monkey arms, like I have, to get your hand in the space between the firewall and A.C. box. Your entrance point is just to the right of the accelerator pedal. Feel around the air box for this foam seal, as a guide it is virtually in line with the A.C. mode switch. A piece of duct tape should secure this piece and allow your A.C. unit to work as it was designed. Good luck!


Sent: 5/30/1998 11:11 P

I just ran out and checked - sure enough the foam is there, it seems pliable enough, but the only thing holding it in place is the tubing that it is supposed to seal. I presume that the slightest air pressure inside the case causes it to open like a flap, and direct air right to the gas pedal. Clever design (ha). The foam seal is entirely on the outside of the case, and I can feel where the side facing the case is marginally tacky. Kind of like anything else foam that was glued 17 years ago - the gasket for the coil cover comes to mind.

I'll be that further dislocation of the foam leads to the problem that many complain about regarding low air flow out of the vents.



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