I've tried to read several posts on the issue. Got into the truck noticed I only had defrost which I guess is default mode. Found a bad vacuum hose and repaired. Still the same problem. Could not find any other leaks. Curious about the vacuum ports/solenoid in the attached picture. Don't know what it controls. Any help or knowledge of the problem and identification would be appreciated. Thanks!

 

Don't forget to check the vacuum line into the passenger compartment that feeds the HVAC controls.

RwP

 

Thanks I'm assuming everything is vac controlled except the fan and A/C.

 

I couldn't find it maybe Ralph knows but there is a TSB for a vacuum issue on some Daks where you have to install a special vacuum diverter on the engine side of the firewall as a design fault allows some vacuum pressure diversion which causes the defroster vent only problem. Or it could just be old leaky rubber o rings and vacuum lines under the dash

 

Thanks all! RalphP it was the line going into the cab. Little bugger was hard to find until it feel off into my hand.