2007 Yukon, front blower works intermittently, rear always works. When the front is working both drivers side and passenger side temp control works, can hear the vents moving when switching between defrost, hand/face, feet. Can feel hot/cold air when selected, just the blower decides when it wants to work or not. Read a few threads about drvers side/passenger side temps different but that is not the problem. Any ideas? I was thinking if the blower was bad it would not come back on, but it does.