2nd Gen Non-Engine/Transmission in cab fan selecter?

[TN farmer]

I just bought a 98. 5 3500 and the fan blows great on defrost but my feet are freezing. I can't get it to blow out of the dash panel either.



Does anyone know where to start looking (vacum, fuse, or cable) I don't know where to start.

 

[DLausche]

Vacuum lines

Mine's a 99 - looked at my handy service manual. Near as I can tell there are 2 vacuum servo motors that deal with heat and defrost. One is named heat-defrost servo motor and the other is panel-defrost servo motor. I think "panel" refers to the dash outlets. The vacuum circuit chart shows that the heat-defrost servo motor connection is the red tube and the panel-defrost servo motor is the yellow tube. Also, from the looks of the chart, the system will revert to defrost in the absence of any vacuum at all. Sounds like you might not have any vacuum at all to the system. The main vacuum line going into the system is the black tube. Normal vacuum looks like 27 kPa (8 in. Hg).



Once again, this is from a 99 service manual. I would think your 98. 5 would be the same, but that is only an assumption. You might want to pick up a service manual for yours. Well worth the $90 or so in my opinion.



I wish you good luck in figuring it out.



-Deon

 

[TN farmer]

Thanks Deon that gives me somewhere to start looking.

 

[Piston Slapper]

symptomatic of vacuum issues. Have heard here before about vacuum line came loose under dash.



good luck,

 

[JNailor]

I had the same experience on my 94. The knob rounded out and wouldn't turn the shaft. If you have a knob, pull it off and check it.

Dana

 

[Gifford]

no vacuum

THe heater a/c system defaults to defrost vents only when you lose vacuum. I bet you've got a vacuum leak in the engine compartment somewhere. Start at the vacuum pump and work your way back.

 

[LHartman]

I had a similar problem. There is a vacuum line that runs just above the valve cover across the front below the windshield. I had replaced my valve cover gaskets and unknowingly snapped that line in the process. Only the defrost would work, nothing to the floor.



Loren

 

[jboehm]

Had the same symptoms in Sept. when it got cold... remembered about the vacuum hose on the drivers side. . , jumped out, plugged it back in and all was fine. Turns out that it had gotten bumped/pulled off a couple weeks before when I replaced the fuel filter. Easy to do!