AC directional switch not working...

[ducrnd]

have a stock 01 exp, 4.0L v6...
I am having trouble that the fan only blows out of the defrost location and no where else.
I have changed the switch ,still nothing. no vent, feet, combination, only defroster....
Any Ideas?

 

[bobflood]

You have a vacuum issue. The mode controller that determines which opening the air comes out of is vacuum operated. When you lose the vacuum supply the default position is defrost only. There will be a small black vacuum line that comes off the intake manifold, goes to a softball sized vacuum reservoir inside the passenger side front fender liner, then connects from there thru the firewall to the mode controller in the instrument panel. Somewhere along that path the line is broken. Good luck.

 

[Spuddy]

^ +1

And, also, plus as well, a vacuum leak anywhere in the vacuum system will cause a default to defrost registers.

Think EGR gaskets, intake manifold gaskets, IAC and gasket, other vac lines (there's only 3 or 4 of them), Etc...

As me how I know.

Nah. I'll tell ya:

I'm still tracing down my partial vacuum leak which causes this only intermittently now - hard acceleration, hills+a/c....

You may need to do a smoke test on your intake system to determine the source(s). That'll be next for me.

 

[Spuddy]

And, as a bonus, since you have a vacuum leak - therefore allowing extra air into your air/fuel mix - your truck is running rich (wasting fuel and clogging yer cats), just like mine.

How many miles?

 

[J_C]

And, as a bonus, since you have a vacuum leak - therefore allowing extra air into your air/fuel mix - your truck is running rich (wasting fuel and clogging yer cats), just like mine.

How many miles?

A misfire will dump entirely unburned fuel through the cats and can damage them, but if your fuel trims are just up due to that unmetered air as a vac leak, it usually just gets lower fuel economy without any cat problems. It's not a situation where I'd avoid driving the vehicle if I really needed to, for fear of causing any further damage, except that if it's something that's progressively getting worse, it could leave you stranded if the computer can't compensate, reaches the upper limits of fuel trim so the engine won't stay running. If you start getting misfires then, you do have a likelihood of some fuel getting to the cats.

A vac leak minor enough that the only thing noticeably affected so far is the defroster (no check engine light), is probably in that subsystem.