Heat and air conditioning in 2000 gmc jimmy rarely works. When it does, it is only

[jeffde23]

in the 3rd setting.? sometimes comes on while driving. Thanks

 

[johnm]

Check the blower resistor. If the blower only works on the high setting, the resistor is probably burned out. The resistor is not located next to the fan switch because it produces so much heat in use- the resistor may be located on the firewall.

 

[kelly_f_1999]

wel heat and cooling two different systems and both controled by switch and fan is another part of both so first heater control switches from heat to ac and fan switch control fan and if fan only works on 3rd setting then its dirty or bad not hard to replace or try cleaning back side with contract cleaner

 

[loves_me_chevy]

maybe its a little simpler... just try replacing the heat/ac crontrol cluster cause it is possible for the knobs to be worn or have a short