I you're talking about blower speeds 1 and 2 not working, then it's the resistor. Instructions on how to replace it are here:
http://www.automotiveforums.com/vbulletin/showthread.php?t=175159
fuel systemfor 1998 chevy malibu
what is the cost to repair password for antitheft system chevy malibu 2001?
how do i change my blower motor on my 2007 malibu
if im not mistaken the heater control has vacuum lines. take off heater controls and see if you have a bad vacuum line to heater box.
Find the source and repair it.
It just cost me $350
Body Control Module
Traction Control
You can't repair an o2 sensor,You'll half to replace it
check heater fan to see if it is working.
The heater actuator motor on a 2001 Chevy Malibu is typically located behind the dashboard on the passenger side, near the HVAC housing. To access it, you may need to remove the lower dash panel and possibly the glove compartment. The actuator is connected to the climate control system and is responsible for regulating airflow and temperature inside the cabin.
Where is the heater control valve for a 93 Chevy van, G-20, 5.O