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Thermostat switch wont change heat to cool air

718 views 2 replies 3 participants last post by  N.Texas 
#1 ·
I have a 1999 7.3L Powerstroke and the thermostat switch wont change the setting from heat to cool air. I got it to change to cool air and than I couldnt get it to switch back until I messed with it for awhile. Now it is stuck on heat again. Any suggestions? I thought maybe it was a vaccum line or someting. How do I check these? Thanks.
 
#2 ·
Could be a vacuum line.. but there is a good chance that the actual mechanism connecting the dial to the electronics/vacuum setup, is disconnected. Is there tension on the dial? Can you tell that you are moving something inside when it starts hitting the blue, and when you turn it back to heat, feel the tension as you are entering the red? Take that front part of the dash off and make sure that it's actually connected to the dial. Somebody else would have a better idea of where EXACTLY it is on these trucks. But this is a common problem in general.
 
#3 ·
I had the same problem on a 97 I owned. I changed the thermostat, check vacuum lines & everthing related. I finally figured out it was the knob itself. The knob was stripped out & not turning the control stem. Boy did I feel like an idiot. One of the guys at work was having the same problem. I told him about the knob & it ended up being his problem as well.

Try pulling the knob off & turning the stem with a set of pliers.
 
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