GMC Sonoma blower control overheats and smokes in the vent position.

How do you determine that the control is overheating and not just the smoke?

Does the heater and cooling work correctly in the vent mode?

it may be due to age of vehicle for one thing as it's 20 yrs old and the blower takes alot of power . check to make sure your grounds for blower and controls are makeing good contact and you have a good battery to body contact. we don't have a schematic for that but the blower gorund should be by the motor and control shold be under dash.

Yes everything works correctly except for the overheating of the switch. It does get hot enough to melt the plastic on the switch and hot to touch in the area where the electrical contact for the vent is. No other switch positions are a problem. All grounds are in place and no short to ground can be found. Again it only does it with the engine running which is very strange.

make sure the grounds are clean and the voltage going to the switch isn't overly high and make sure you have a good body ground to battery and engine to body ground. Camaro's in the 70's would burn thier shift cables and get stuck in drive even though the shifter would work and that was the problem the engine to body and body to battery ground was no good so would ground through shift cable and melt it when a/c or blower was on high.

Thanks for the help! I think it's fixed for now. There are 3 relays in the circuit for the compressor and blower. Two are together and work together. I took these apart, checked with a 12v supply, and found 1 not working. I freed up the moving parts, cleaned the contacts, made sure they both worked and re-installed. No more smoke so I will replace with new relays tomorrow.

why don't you just replace those instead of screwing around cleaning them? they will just fail again.