Ventalation system - Thumping

[Craig]

When I start the truck it thumps for 10 seconds under the dash and again for 10 seconds when I turn the truck off. It sounds like the flap in the ventalation system wacking back and forth. I also notice when feeling around under the dash where all the vent system stuff is (Flat black surface near passenger side of tunnel) it was real hot to the touch. I was running the AC at mid temp

[Garth J]

Mine did it too.. There is a solenoid under there that opens and closes the vent door for inside and outside air.
I just set the A/C on normal and unpluged it ..It looks like a bear to change.
the hot could be just the air return to the condenser...Garth

[Craig]

Found the wire and unpluged it. It was between the blower motor and the firewall. Thanks.