This question is a little out of season but if I don't get it fixed this summer, I never will.

Anyway, my problem is that I dont think the vent that lets outside air into the cabin is closing, ever. Durring the winter cold air will blow out of the vents, except when stopped. In the summer the A/C works but I can tell it's still mixing with outside air.

I've been told there is a valve somewhere under the dash that 'might' be the prob and that it's next to the vaccum bulb, but I haven't been able to find it.

As far as switching between defrost, vents and lower, all the controls seem to work. Any ideas would be great!

Dayton




<img src="http://www.geocities.com/schnikies79/car.jpg">

"The road goes on forever and the party never ends."

Dayton... some things to check, because you actually didn't state what mode(s) the system was in when this happens. I'm also going to "assume" you have the plain Jane manual a/c heat system, and I will run you through all modes, so they may be checked. Statements like, they seem to work, tells me you are not quite sure how/if they are working properly.

Before starting, check under dash/footwells to see if some giant with size 23 shoes, or some little lady with size 5's, may have kicked/pulled off vacuum lines under there. Sometimes it's as easy as that. See if any are pinched closed.

1. Under L/F fender, below battery you will find a black plastic vacuum tank., it's round usually. Gotta lay on ground usually to see this. Black hose from engine supplies vacuum, Violet hose goes to control panel. Make sure the tank isn't cracked & leaking. If all is well, continue, otherwise fix leak(s).

2.Temperature selector(door). Move arm back & forth fairly fast. You "should" hear a thunk, as door hits its stops in either direction. No thunk, no problem, cable and door is adjustable.

3.Checking systems modes.

HEATER temp at HOT...blower runs on low speed, air flows from floor outlets, and VERY slight flow at defroster ducts.

DEFROSTER...air flows from w/shield ducts. Compressor may cycle on/off.

VENT...OUTSIDE air flows from dashboard vents. Compressor stays OFF.

BI-LEVEL...temperature set to COLD. Air flows from dash & floor outlets. Compressor comes on, engine fan comes on.

NORMAL...air from dash... compressor runs.

MAX(imum)...Blower noise will get LOUDER as the OUTSIDE AIR DOOR CLOSES.

Tip: under dash, where blower motor is you will see a series of plastic squares with a flapper door. This usually is where the MAXIMUM...recirculating/outside air door is located. You can actually watch/hear it open/close.

This should keep you busy for awhile :> good luck. Sounds like a birch, but really not all that complicated.

Alan

Alan,

Thanks a load for the tips. I went through each one of your suggestions and everything seems to check out. The only diffrence is that the vacum bulb is under the dash on the right side, there is nothing under the battery.

Okay, the modes that I have a problem in is defrost and heat. If i'm driving down the road when it's cold outside, i get cold air, but the second I slow down for a stoplight or whatever, I get heat again. Of course when I take off again, it goes back to cold. Thats what led me to believe that the vent is not closing.

I know it's not a thermostat problem because the engine temps are normal (i've checked them with an infrared temp sensor) and I've put two thermostats in it since I've had this problem. It has a 190 now if I remember correctly.

I was not able to hear the 'thunk' you described so I peeked under the dash when moving the heat/cold selector. I saw the cable moving and could hear it there.

Should the outside air vent close when in heat/defrost mode? Why else would I have cold outside air blowing in?

Dayton


<img src="http://www.geocities.com/schnikies79/car.jpg">
'85 Cavalier, 2.0

"The road goes on forever and the party never ends."

Dayton... first I goofed, the location of vacuum canister on cars with cruise control (mine) is under battery/fender area. The rest are where you found yours. :>

Now... in car air and outside car air is determined by the position of the recirculating/max mode door. This either draws air from, you guessed it, inside the car to quickley heat/cool car... or from outside at the cowl area. This is located at the far right of plenum, looking at dash from seat, over by the blower motor.

This air flows thru the evaporator core... all the time hot or cold... and goes to the left where the temperature door is located. So far ok?

Now this door either deflects the air up to the heater core or down and out thru the dash vents. If you have heat/defrost mode set the following happens.

Air , that's coming thru heater core is diverted to either the defrost or footwell/floor vents.

So by your own description as you slow down/stop you get heat. Fine door is diverting the air thru heater core... as you drive air gets diverted down, as in a/c mode, even though the a/c's off, and actually what your getting is the outside cold air. Check for vacuum leaks/pinched vacuum tubing, etc that's allowing the door to move into the a/c mode.instead of heat mode.

The only thing you didn't state was WHERE the cold air at driving is coming out from, and where the hot air at stop is coming out from. You just say it's hot/cold????

Alan