99 tahoe I changed the thermostat, flushed the radiator and the heater core!!! still no heat! my switch only turns the fan on when it is on high no other settings work could it be a switch or maybe a watter pump??? I need heat please help!!!

99 tahoe I changed the thermostat, flushed the radiator and the heater core!!! still no heat! my switch only turns the fan on when it is on high no other settings work could it be a switch or maybe a watter pump??? I need heat please help!!!

the resistors that control lower speeds is n/g, this is located in air plenum in dash on passenger side access is from under glove box. if no hot air at high speed then your electric motor heat blend door is also n/g or stuck...........common problems with this vehicle........the reason you only have high speed fan is , the resistors are not in that circuit.....after market resistor module is 20-30.oo...