The heater/ac fan only works on speed settings 4 & 5

SOURCE: Heater blows cold, and fan switch only works on 4 and 5

working on 4 and 5 speed that the resistor that broken cold air you got to move the selector to see the motor that move the trap hot and cold sometime when the motor was not move to the hot side for a long time its jam the motor on the passager side under dash put to hot and gently tap the motor tanks pierre

SOURCE: Fan speed switch only works on #5

Call your local GMC Dealer and see if they have the climate control panel in stock. What happens is the circuit board on the back of the panel shorts out. The panel comes as an assembly and is very easy to replace. Don't go with a wrecking yard piece. I made that mistake once and it didn't work either. I got one from the Chevy dealer and it worked perfectly.

SOURCE: Heater/ac switch speeds 1 and 2 don not work in 99 Silverado

you need a resister found under your air duct by the passenger floor under dash board auto zone sells these for about 25.00 you may as well buy cabin air filters while your at it . 1 of the screws will be a pain to install back into the duct work I left mine out didn,t make a difference . you might have to order it as they are a comman item oh you will need a vacuum to clean up mess from cabin air filters .this is not a hard job .

Jerry Koski

• 443 Answers
• Posted on Apr 22, 2009

SOURCE: HOW DO I FIX THE AC/HEATER BLOWER FAN ON MY 2004

Your switch acts as a reastat which adjusts your speeds your switch is going bad so you only have the two speeds left on that reastat.. thanks Jerry

SOURCE: heater/AC fan only works on the 4 and 5 settings.

Either the switch or the resistors on the blower. Get shop manual remove switch and jump terminals the manual tells you to do to check switch. If a-ok then do checks for the resitor on the blower motor. Hopefully its the switch.
Good luck

Testimonial: "great trouble shooting. This is very helpful. It was the switch"