The temperature control works on the dial, the fan level works, but its stuck on defrost. It will do defrost on all the settings. It is a high miles truck with about 193K miles and used on a farm most of those miles so everything under the dash is very dusty and dirty. My therory is that if I pull it off the ac unit under the passenger side dash and clean it up and put it back it should work again. Any other ideas out there?

 

Have you messed around under the hood much? A vacum leak will cause this. Do a search on AC problems on this site i have seen numerous threads about it. I had the very same problem and it was a vacum leak.

 

dezlsmkr, is right... You've got a vacuum leak somewhere. It a safety factor that DC made the defrosters the mode it falls to when the vacuum fails. Check around...

 

I had my plastic vacuum line fall down onto the exhaust somehow, and it melted the line, then we only got defrost, so I third the vacuum recommendation.

Chris

 

That is such a better thing then taking the dash off and the ac unit off and repairing the ac unit. I will do that tomarrow morning.