I am having an issue with my '05 Yukon Denali XL's heater blower. The core is making heat, however, the fan sporadically will not come on for long periods of time. The fan for the rear seats (both upper and lower) seems to be working fine and comes on/adjusts intensity with the controls. I have tried many things from restarting the vehicle, to shutting the heat/AC control panel off. Is this some sort of thermostatic control issue? It seems to happen mainly on days that are colder than normal. When everything works, it works great and heats the vehicle very well.
