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Could be a number of thing's ! Testing the electrical circuit is the way to find out what's wrong . Using a wiring diagram and a DVOM - digital volt ohm meter . Videos on youtube showing how to test it ! Without testing i would only be guessing . Does it work in high speed ? In high speed it by-passes the resistor . If it doesn't work in any speed more then likely the blower motor is the problem !
The HVAC control assembly applies ground to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:
• Low speed--3 resistors
• Medium 1 speed--2 resistors
• Medium 2 speed--1 resistor
When the operator requests High speed, the HVAC control assembly applies ground directly to the blower motor through the high blower motor control circuit. The resistor card has a fusible link which, if blown, will require that the card be replaced.
Under the dash is the heat box and it has two levers on it. One is for changing where the air comes out (floor, vents, defrost) the other is the BLEND door and that controls hot and cold. Look for the levers on the door, move the controls and see which one is not moving or if they both move it could be the DOOR inside the box that is broken off.
This is typical of a voltage resistor pack problem, it controls the different speeds of the fan.
I'm not familier with your Tahoe, but this is usually installed right in the air stream of the fan to keep it cool.
Look for a connector block with 3 or four wires, installed under the dash of passenger side, right ito the air tube moulding, very close to the fan.. 2 or 3 screws, should be quite easy to replace it and inexpensive. Just be sure to install the new one all the way before trying to turn on fan. It needs the blowing air to cool or may burn out immediatly.
Check the relais module located inside under the rh side of the heather box you can see the connector most of them need to be replaced as they burn out you may need to replace the blower motor as well,high amp draw caused by faulty bearings will overload the blower motor controller