Why is it blowing warm on and off on the driver side and blowing cool on the passenger side?
Here's is a little background and a couple of thoughts. Turning to the background, first. The heater/air conditioner system in your 02 uses the same set of ducts located in the instrument panel. In turn, those ducts are linked to what can be considered miniature version of the cooling system in the engine compartment (yes, this is a greatly simplified version). The whole system, in fact, is run off the main heater/ac system, however, it has a separate series of controls so that it can function properly.
When you dial a temperature, a signal is sent to the heater/cooling system telling the system to open a series of baffles, directing a flow of heated or cooled anti-freeze/coolant to the proper "radiator" behind the face of the instrument panel. In turn, the fan system activates a series of doors behind the instrument panel so that the flow of air is directed through the "radiator" and into the passenger compartment. This is essentially the heater/cooling system work.
Now, you say that the driver's side is hot, while the passenger side is cool. What has happened is that the flow of heated coolant that is supposed to heat the passenger side of the duct system is blocked. Since there is no heat to warm the air that is flowing past the fins of the "radiator," the flowing air remains cool to cold, depending on the weather and ambient temperature. The result is that one side of the car remains cool. And, since the other side of the "radiator" is normal and the air is heated, it is warmed.
That is the most likely explanation for this.
Another possibility is that the baffles themselves are stuck and the coolant that is supposed to be directed to the passenger side is not being directed their.
Either way, your technician has some work ahead.
2002 GMC Envoy...
on Jun 05, 2015