Well...I have a `96 SSEI and my heat does not blow cold, I have just replaced the heater core, Thermostat, AND the control unit(which I paid $198 for from gmpartsdirect.com) This has not fixed my problem...I know the heater core is working fine because the inlet and outlet hoses on the firewall are hot. The thermostat is fine as the car runs at correct operating temperature, and doesnt overheat. The coolant has been flushed and filled, so there has to be another issue...I know there is a cluster of vaccuum lines that run to a circuit board, could this be bad? and if so does anyone know what its called...anyone with any info for me would be a total savior ...I dont really wanna take the car in for service if I can fix it myself...Thanx for looking, Gary.

Sounds like the air mix door is not opening? Check connections to mix door motor, inspect linkage. fuses ok?

fuses cool...i will check the mix door motor..is this is whats powered by the vaccumm lines? thanx bro, Gary

The pic I have is clear as mud, but you have to remove the lower air cover, its on the left side of the console?
Theres air inlet and an actuator for driver and one for passenger.

Do you have access to a code reader? the hvac system has a lot of codes to help troubleshoot.