Climate Control

[mlc596]

I have a 97 Tahoe and when I turn on my A/C it blows from the dash vents and the floor vents and when on defrost it doesnt blow hardly at all. Also when every thing is off and im driving down the road air comes from the vents. I am trying to find out whaT PART IS BAD. I thought it might be a blend door but now I am not so sure plus there are aparently more than one blend doors, im not really sure. Any hints to what my problem could be would be very helpful.

 

[SunlitComet]

in defrost mode outputs does it blow out just out the top below windshield or top and upper dash face vents. and when off which vents are leaking air. or are they seriously blowing.

 

[mlc596]

It blows hard when moving and everything is off and the defrost comes out the top and front face vents.

 

[SunlitComet]

you are likely to recieve a little leakage air when off because the recirc door lets in air from outside and out the vents it the body by design. if it is really strong when moving and not when not moving you may want to check the end of front doors to make sure you dont have the access panel missing or extremely worn out door seals. at speed these can have low pressure around them and to fill the vacuum void they create in the cab it will suck air in threw the hvac. a missing weather barrier film in the doors can aggravate the issue. you can reduce this by using the recirc button to close off outer air intake. when system is off and the air blowing occurs at speed where is it exactly blowing from? you have three door assemblies. one for mode/output vents, one for temp control and one for the recirc door. some things to note as well, lower vents exit thru a few small oping below the dash and if applicable one vent under each front seat on the drivetrain tunneling. the fronts exit thru about small squarish vents. the defrost vents exit thru about 5 i believe so the defrost vents coupled with a smaller transfer duct in the main housing will be a bit slower in air speed. sometime the seal between the distribution duct and main housing can break down too causing leaking in the dash. the pic below will give you an idea of the flow.

 

[McFizzl]

Yep. mine does the same thing with constantly having atleast some air coming out. I always leave it all the way on cool if not using it otherwise it leaks out hot air. I have the same problem with it coming out of the wrong vents then 2-3 minutes later i will hear the blend door actuator finally switch them. Turning the fan on max seems to somewhat remedy my issue.

 

[SunlitComet]

yeah i am thinking for you fizz that the controller or fan switch is the problem. i know when fan shutdown actuates controller shutdown the motors go to a defualt position. what they are i will have to find out. mode and recirc are easy the tep door on is harder to find out cause there is no linkage to see and when the fan is off you cant feel the heat or cold difference. i wish i had spare hvac box to experiment and document what happens for others to see. the controller can do some weird things sometimes too. at times with RAP on just sitting there in the seat i hear them moving around on their own. i know it is not the recirc motor so when i hear it happening again i will look and see if it is the mode motor since you can see that one. if i had spares around here i could find out what part on the board that does it or if it is a system voltage weird thing.