Feel the heater hoses, they BOTH need to be hot, if only one is hot, the heater core is clogged, if both are hot, the temperature blend door inside the plenum(box) is stuck, either from rust on the shaft, or a bad actuator. If both hoses are cold, check your thermostat. If both are hot, have the truck scanned for codes, this will reveal a bad control panel or door actuator.

Answered by merlin2021 (expert)
18,145 answers provided

The heat in the front of the truck works great..is the heat system a different system...?

Response from schoolman
3 questions asked

Yes, if it's the rear unit, the same rules apply back there, plus a check of the heat system via a scan tool capable of reading "B" codes. This will pinpoint the problem part. This is a complex system, and without a scan, you will be just guessing at what part needs replacement. Checking the hoses is too see if the mechanical portion of your system is working, but it also has many electronic sensors and actuators to perform the work.. Is yours an auto temp or manual system?

Answered by merlin2021 (expert)
18,145 answers provided

There are three ****s ceiling mounted above the rearview mirror that control the rear cabin only.... **** for fan control with auto/ manual setting, temp and vent location The main system on dashboard is auto for front passengers only?

Response from schoolman
3 questions asked

Ok sounds like auto system, here's a diagram of the parts and location, I do recommend a scan!

Answered by merlin2021 (expert)
18,145 answers provided