Took my 07 2500 to the dealer for intermittent failure of the fan speed selector on the temperature A/C control. They replaced the temperature control head unit. It is still doing it. It will work then quit blowing air, A/C is still cooling and I can change the blend door settings but no ability to control fan speed. Any ideas? where does the other end of the harness that plugs into the control unit go?

 

The fan motor gets + power when key is on from the TIPM.

The fan speed switch completes the circuit to ground/negative either through a resister block on lower settings, or directly when on high.

If you lost all speeds but high, then I'd be looking at the resister block. It is mounted on the bottom of the HVAC case, to the left of the fan blower.

When you say it quits blowing, do you mean the fan stops running? A few folks have had motors fail.

If you can still hear the fan but not moving air, check the fresh/recirc door. It is right above the fan, and has been known to break and fall over the blower wheel. Pull the rear corners of the glovebox inward while you tip it out, and you will have a good view of the recirculation intake grille, or just pull the fan motor and look from there.

 

It completely stops blowing air. The recirc door is working. When it stops working even when I turn the fan to the off position the yellow A/C light stays on. When it quits it will usually start working again the next time the truck is started. Seems to be electrical problem.

Was hoping somebody had a similar experience and could share the fix, the dealer just wants to replace parts ***** nilly.

 

My 06 is doing the exact same thing. The blower quit turning, the yellow a/c light stays on and when you turn the truck off and wait a minute it starts working and stays on. It appears to happen only after it's been on for a long time. The Florida heat in August probably doesn't help.

 

Earlier trucks get key on + directly from the ignition key. There have been some threads about charred wires under the steering cowl, and/or charred ignition switch.

Sometime mid-06 I believe they changed so that the fan motor gets + from the TIPM.

It might be worth it to take the cowls off the column to look for anything charred, and maybe take voltage meter readings when it acts up.

Be sure to disconnect both neg battery cables for a few minutes before working around the steering column, so as to disable the airbag.