Defective ballast resistor pack.
OTHER :It sounds like it could be the blower motor relay / resistor. I replaced mine today in my 2001 Chevy Impala. It was next to impossible since I heard that the way to get to the resistor was to remove the blower motor housing and repair it that way. I instead removed the blower motor and got to it that way. The two screws in the back are knuckle busters. Good luck and I hope you have patience or enough money to have someone else repair it.
The blower motor speed resistor is burned out.
try replacing the blower motor resistor
Check the low speed relay and the resistor at the motor
do you mean the speed of the fan? if so, it'a relay generaly near the motor of the fan. If it's the heat who only came at high speed, you need to add some antifreeze.
blower motor resistor is burned out
The blower motor resistor pack is bad.
2004 Chevy express van, heater has no high speed, at one time the blower stayed on even when the ignoton was turned off therefor draining the battery,
you might need a new switch.
The blower motor speed resistor is burned out. The high speed function bypasses the resistor. The speed resistor is generally located near to the blower motor.
Defective heater resistor pack.
If all speeds do not work, suspect the fuse, the switch, the switch connector or the blower motor. If only high speed works, suspect the blower motor speed resistor. If low speeds work and not high, suspect the blower motor relay.
Maybe because your climate control system needs to be repaired....