I'm stumped and as usual could use some help. Why would my fan blower work in the on key position and then nothing once started. I still have power to C1 10BR going into temperature controller once then truck is running. Voltage increases to C1 10BR while running. But I don't have power to C4 10TN or C7 12DG with the truck running and the controller turned on. Ignition switch, blower fan, and resistor are all relatively new. I even switched out the hvac unit for one that I know works. Heck, the one that was in there works fine until the truck starts. I don't get it. One thought I had was after removing all a/c components from the engine bay maybe the two unconnected pig tails need a jumper wire or a ground of some sort. I know there's a great troubleshooting post already but I feel like I'm missing something easy. If there is such a thing as easy. Thanks for any ideas out there.

 

Is your ignition switch located down on the column and actuated by a rod? NOT a tilt wheel system. If so your rod adjustment may be off. I have noticed that my windows will not operate sometimes if the key is just a little off and I have to tweak it back to the right to get the windows to work after I start the engine.

Edwin

 

I would replace the ignition switch. Doesn't matter which type it is, too much juice goes through those small contacts. Putting large loads on relays take it off the switch.