2023 Peterbilt 579 heater blowing cold air.

Try unhooking the ground on your battery for a few minutes and see if that resets the computer. Other than that the dealer will probably have to hook up to it and see what’s going on. Could be as simple as needing a software update or you could have actual component failure. What did they say the problem was in December?

 

Most commonly needs a temp blend door actuator. High failure rate.

 

Amazing how many problems I’ve solved by using the battery disconnect.. I’ve had a similar problem as @bentstrider83 but it was the sleeper blowing cold. Now if I could just figure out why fourth gear ( fan speed 4) ain’t a workin..

Mines a 2023 also..389 but I’m sure everything is the same.

 

I had the same issue when I bought my 2023 Pete 567.

Probably not the coolant but check anyways. Then when starting the truck, hold down your thermostat gauge and vent control for 5 seconds. Yes, it sounds dumb but worked for my truck everytime until it reset to automatically blow heat. Once and again, it will blew cold air espeically here in Canada being minus 10 Fahrenheit at times is a real issue.

 

Are your heater hoses hot where they go thru the fire wall ?
If they are you got heat to the heater core.
The fresh air vent door may be stuck open.
Duck tape up the fresh air vent on outside of cab.
You should have heat now.
Actuator's may be stuck.

 

Glad to hear it.