2018 Pete 579 little to no heat (2024)

OK, first post here, looking for a little help. I'm in a 2018 Pete 579 and getting very little heat in the cab. The sleeper heat works fine, so I won't freeze or anything like that, but worried about the defroster not keeping up in the snow. So far, I've changed the heater controls, the blend door actuator and even taken the heater core out and cleaned it. And the water hoses are both hot coming out of the heater core. When I was changing the blend door actuator, I stuck a screwdriver in there, turned it all the way to the left, and got heat but not for long. It will give me heat for just a minute, then it cools off to just kinda luke warm. Nothing I've done has really helped much. I've got it all back together now, and out of ideas. So, is there anything I'm missing, or not thinking of?

Sounds like a either a CCU issue or a blower issue. The blower in my 17 579 failed and started doing stupid #### and had to be replaced. Though they also said a lot of times it just needs the CCU to be flashed by the dealer.

There is a wire on the backside of the motor that over time flexes back and forth and breaks inside the actual insulation and can cause a short according to the tech that replaced mine.

If you turn it off for twenty minutes, then turn the heat on, is it hot temporarily? Like you mentioned when moving the duct door.

Thst usually is a heater core issue, Plugged inside.

I assume nobody has messed with the heater hoses since your bunk works?

Yes, it does get hot, but not for long. It goes back to luke warm fairly quickly. I did check the hoses when I started this little project, and the return hose was barely warm, even though the supply hose was hot. So, I thought i found the problem. Took the heater core out, blew air through it in reverse, then forward several times. Actually, got good air flow through it by the time I was done. Put it all back together, warmed the truck up again and both hoses were hot! So, I assumed that would have fixed the problem. But it didn't really help much at all.

Blower works fine. just blowing cold or luke warm air.

Going off your description, I'm staying with the heater core being your problem

And you may very well be right! At this point, Im about out of ideas. I mean, there really isnt that much to a heating system, on any car or truck. Its just take air, blow it across a hot heater core, and presto, you have heat. But this one is kicking my butt!

Door for outside air broken ?
Duct tape over the screen inlet may give results.
Mine is up under the passenger side air breather ( 2006 ) kind of hard to see if Peterbilt has not moved it.

You would be suprised. When mine failed it started blowing backwards and ended up melting a hole in the plastic intake tube (still not sure how) and gave me a result pretty simular to yours. That said id have the CCU reset just to rule it out before you shotgun more parts at it. If nothing else it may have codes to help you narrow it down.

Regardless good luck. Tracking down these kinds of issues are a henti level pain in the rear.

Truck is too new for anything to be plugged, I say, maybe a pressure problem. I think if a bad head gasket, pressure builds up in the system, and won't flow correctly. The bunk heater may come from a different area. Water pump maybe?