2nd Gen Non-Engine/Transmission Stuck on Defrost?????

[Devil Black Diesel]

For some reason my air will only blow out of the defrost ports regardless of the setting on my A/C control dial. All functions work (A/C, Heater, and vent) but they will only blow out of the Defroster ports..... anyone have any ideas?

 

[PC12Driver]

The dampers default to the defrost position if there isn't a vacuum signal. You probably have a hose off somewhere, or the hvac mode selector switch is bad (it's basically a valve that routes vacuum to the various dampers).



How's 4wd work? It's vacuum controlled too (which would tell you if your pump is good or not).

 

[Devil Black Diesel]

So if I test my 4WD and it works that means i have a problem with the vacuum plumbing?

 

[DBraunig]

The vacuum supply to the HVAC actuators is under the hood on the passenger side, follow the a/c lines through the firewall and you should find the black vacuum supply line right there with the a/c lines (i have seen it drop down and melt on the exhaust manifold). see if it is cracked or collapsed anywhere. disconnect it and start the truck and check it for vacuum. if the line is ok (follow it all the way across the engine bay) and the line has vacuum, then you have a control panel issue, or a problem inside the truck with the HVAC lines/actuators.



Dave

 

[justinp20012500]

Just went through this...



You have to take the whole shifter and shroud (cup holders) to get to the actuator.



My arm had fallen off. Kind of a pia, but nice to have it fixed.

 

[EDudley]

Happened on my 97, it was just a vaccum hose that fell of under the hood, luckily it was out in the open. I'd starts by checking all the easily accessiable vaccum lines, then go from there. good luck

 

[Joe G.]

When you check under the hood make sure you check the part of the vacuum hose inside the connector above the exhaust manifold. It can melt shut there and you can't see it unless you take the connector apart.

 

[McLaughlin]

Another easy check is to see if your cruise control works. That runs off the vacuum also. I've seen the vacuum hoses separate at the connector on the firewall a couple of times. The connector is over or just a bit right of the intake manifold.

 

[Missouri Mule]

Mine did this and it was a pinched line under the dash.

 

[Devil Black Diesel]

Thanks for all the good info. I'm sure it's a disconnected line because I just had a LP replaced by one shop and I also had some other guys under my hood who were doing some work around my turbo/intake. They probably knocked something loose or pinched a line... .



I really hope it's not under the dash. I'll report back when I find out what the problem was. Unfortunately I won't have time to look at it until Christmas.



Thanks again everyone.

 

[rono]

Mine did this twice. Both times it was the vac. line had come off the fitting on the back of the vac. pump under the Inj. Pump. Going to defrost only is the default setting if you loose vac.

Ron

 

[Devil Black Diesel]

Well I finally had a chance to get under the hood yesterday and I found a vacuum line had been knocked loose above the exhaust manifold and it melted a big hole in it - exactly what DBraunig said. Thanks for your tips guys. I just wrapped a piece of electrical tape around the line to seal the hole back up and everything is working properly again.



Thanks Again.