89 Peterbilt 379 cab heater problem

[midmac48]

Have a problem with my heater functions , if I put it on defrost it will be on defrost for a short time and then will lose the defrost, if you switch to other function and return to defrost it will work for a while. Anyone come across this problem.

 

[waynejd]

i have a problem with my 2000 379 heater controls. i have no control over any of the functions such as temp. blower positions, rec./fresh, no power to bunk, and fan wont shut off, but the speeds do work

 

[lightingboy]

Have a problem with my heater functions , if I put it on defrost it will be on defrost for a short time and then will lose the defrost, if you switch to other function and return to defrost it will work for a while. Anyone come across this problem.

Have u checked the lillte cilinder that swiches the little door inside the unit.it might be damaged and will cut off and open the little door back to the a/c side.
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[Larry]

I know the problem....It's them dog gone Peterbilt's. LOL

 

[lightingboy]

i have a problem with my 2000 379 heater controls. i have no control over any of the functions such as temp. blower positions, rec./fresh, no power to bunk, and fan wont shut off, but the speeds do work

It might be the control panel I had that problem on mine but mine was on a 2006 379 I now have a 2007 379.the board could have gone bad. Or if its air powered like kw the line get pluged up and need to be cleaned out or may rubbed together and have a leak and may be geting the air it needs to work.
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[gottago]

I have the same problem. Did you find out what was wrong

 

[midmac48]

Heater defrost problem

Hi!
No I have not found a solution as of yet will post when I do

 

[midmac48]

Have checked alot of things no solution yet, will find a solution one of these times

 

[Flatbedpete]

Have you checked the electrical actuators. These operate the vent doors. If you can remove one, look at it as you switch climate control. you should see the little metal ring inside move. Replace them if they don't. There will be two of them, one under the dash for the front, and one under the bunk plywood for the bed on top of the rear unit. I have seen when one doesn't function right affect the other. I had purchased many on ebay for about 10 - 15 bucks and keep a spare set in all trucks. Simple fix