So I'm a little confused with this one. When you have the key on or truck on the heater fan doesn't do anything. But after you drive it for maybe 10 minutes it kicks on. It's really weak but hot air none the less. I'm thinking it could be wiring or a relay but would like some input if someone understands my problem.

 

Dirty contacts in the heater/ac control unit on the fan switch, failing fan resistor, failing fan unit, or just a loose connection at one of those three places.

I'd guess loose connector maybe first since it comes on eventually, and maybe the "percussive" test on the fan unit second.

 

Alright. Thank you. I'm actually going to assume its something in the motor compartment. It has a newer motor and the previous owner messed up a lot of connectors and electrical components. What should I check in there?

 

Uhm start with all the plugs are clean, not overly loose(female spade plugs tight) and fully seated(plastic lock clips all the way locked).

heater TS starts on the second page of this FSM section