No heat in 2015 Peterbilt 579

No heat in 2015 Peterbilt 579. I turn the deep frost on to max and it will cook you out of the truck. When I turn it to just regular defrost I get nothing but cold air. The actuators appear to be working to opening the doors to change from foot to defrost to chess vents. But nothing will come out other than cold air. Just don’t understand why I have heat on max defrost only.


If this post sounds funny or looks funny in the spelling, I’m using voice to text. Sorry

 

Likely a bad actuator in the system. That said rule out a blown fuse first using a tester. Then rule out that one of your taps is closed on the heater core. Easy to check and cheap.

If there is no blown fuse and the taps are open then you need to have a dealer run a test on the system, i think its called an esa? It will tell you exactly whats wrong and may just be you have the old software still and a quick update will fix it.

 

Esa is up to date.

 

I have all positions get air when their prospective selection is made on the climate control but is cold. So those doors are working. I get cold air on defrost normal. But if I hit defrost max it’s hot. When I turn off the max, I can feel the warm air come from any vent just briefly until that air cools again. Almost like the blend door is closing on anything other than max defrost.

 

Hummmm check the heater core lines. Are they warm to the touch? Also check your coolant level.

Also could still be one of the actuators sticking but the one doe the defrost opening or being forced open by the warm airflow.

 

Lines going to coil are hot. Both. Coolant full. I hate going to the stealer but looks like I’m gonna have to

 

Yep sadly i think so as well. If the lines are hot, coolant is full, fuses are all good and there is nothing obviously broken or leaking then its either a deeper electrical problem, a bad actuator, or if your really lucky a bad control switch. The max defrost at least on my 17 579 is on a diffrent wire and circut then the control knob.

 

Fresh air / recycle air door not shutting ?

 

It operates fine. Can definitely tell a big difference from open to close

 

Check your cabin air filter & look at the heater core itself. Make sure the fins are clear of any gunk or debris