Bad blower resistor?
Sounds like the blower motor resistor. Should be near the blower motor under right side below glove box!
The blower may simply have burned out. If the blower is out then the heater probably still works.
Why does my 99 silverado have no heat and the ac fuses look good and blower motot works great
The heater blower motor speed resister is burned out.
Defective blower motor resistor pack.
Depends on what you mean by heater will not work. If the blower motor will not work, it can be a blown fuse, bad blower motor, bad blower motor switch, or a defective blower motor resistor pack. If you mean that the blower motor works but there is no heat, then it can be a clogged heater core, thermostat stuck open, or defective heater control valve.
Heater core
The blower motor speed resistor is burned out.
The most likely cause is a bad blower motor resistor.
ABS and blower motor are unrelated.To fix blower motor, read this:http://www.ricksfreeautorepairadvice.com/diagnostics/blower-only-works-on-high-speed
Check the blower resister
Resistor on the heater blower motor has failed