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
Find the source and repair it.
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.
It just cost me $350
Body Control Module
Traction Control
You can't repair an o2 sensor,You'll half to replace it
Where is the heater control valve for a 93 Chevy van, G-20, 5.O
check heater fan to see if it is working.
How do I repair heater that won't shut off in 1998 chevy s-10 zr2 pickup?