Here's what I have. 02 X 7.3L 4x4.

Heater will work fine. Then out of nowhere just blow cold. I can turn it off then back on it'll blow hot for 1 minute or 20 minutes. Then out of nowhere blow cold again. It doesn't matter if I'm highway driving or city driving.

I'm kinda thinking it may be the door in the duct that's just closing. I real don't know.

Thanks.

 

See HVAC FAQs. Link is in signature below.

 

Thanks. Got it.

 

It sounds like a blend or other door malfunct.

 

I think its the blend door actuator too. I had orileys special order mine. If you take yours apart and find your plastic gears are stripped let me know. I have my old one at home with good gears. You can just swap the gears if that's the case. Mine was the motor inside.

 

Look at the following thread..

Click...

On page 2 I posted some general troubleshooting logic, and (gasp) pictures. The part number I posted for the actuator motor assy is accurate.