A/C & Heat all going thru Defrosters

[sspanthony]

Recently had to replace my heater control because the indicator switch would not switch from panel, floor, mix, etc.... Every setting would cause the air to flow through the defroster at the top of the dash as a default.

I replaced the complete heater control unit and now it switches correctly as it should "BUT" everything is still coming thru the defroster ??? I checked for vacuum leaks but didn't see any apparent issues?

Anyone ever run into this ??

[FoxChassis]

Very tiny black plastic vacuum line running across the top of the firewall. That feeds the climate control assembly. Check that line for vertical breaks or horizontal splits. That's the most common place for a vacuum leak. There are other places of course.

Here is a diagram of the HVAC vacuum controls, courtesy of TMoss (Tom Moss) and veryuseful.com:

http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

[1988Bullitt]

Has to be a vacuum leak somewhere, default position with no vacuum is defrost. The vacuum line mentioned above is a good starting point as it is the main vacuum line to your HVAC system.

[NoDrama43]

Recently had to replace my heater control because the indicator switch would not switch from panel, floor, mix, etc.... Every setting would cause the air to flow through the defroster at the top of the dash as a default.

I replaced the complete heater control unit and now it switches correctly as it should "BUT" everything is still coming thru the defroster ??? I checked for vacuum leaks but didn't see any apparent issues?

Anyone ever run into this ??

I have run into this. Behind the glove box is a series of vacume lines that intersect and connect in a "group" or "junction fitting" (for lack of better words). When I had that same exact problem it was because a line had pulled loose from this fitting. Once I plugged it in the problem was fixed.