2000 gmc yukon, no front heat ,good back heat

2 things to check. 1 check heater hoses going to the front haeter core, both should be hot with warm engin. 2 with engin off and ket on, turn or slide the hot/cold knob/lever from hot to cold and listen for a door moving in the hearter housing under the dash. you should be able to hear some thing move, if not promlem is in the control asembly or in the heater/ac housing. let us know,mws919

Both hoses are hot,fluid level is good,hear flappers moving when I change temp dial.

ok, here comes the trickey part. if both hoses are as hot as the top rad. hose, you are going to have to remove the blend door motor from the housing and turn door by hand to make sure it works. just because you hear the servo motor run doesn't mean the door is closing. anyway do this with eng. hot and see if you can change it from hot to cold. now to find the servo motor, work the dial and feel the servo's under the dash on the heater/ac housing, the one that viberates in your hand is the one. let me know how you make out with this. mws919

Do I need to remove anything to get to the area where the motor is? Wife is driving car daily still so I don't want to tear open the dash if I don't have too yet.

ont sure. you'll have to remove the under dash panels to check servos, that part will not stop any one from driving it. but depending on witch servo it is, that may be another story. if you can see 2 out of the 3 and the 2 are not viberating when you switch the blend door, then the 3rd one you cann't feel, might need housing removel to get at it. check the ones you can get to and let me know. mws919