Hello All,
I have a 1998 Suburban. It has separate controls for the rear temp and front temp. When we have both controls on cold (and the AC button pushed in), the front vents don't get cold with the AC running whereas the back blows ice cold. With both controls on hot, the back vents blow cool and the front vents blow hot air.


I'm suspecting the mixing valves are not working fully. Does anyone have any other ideas or know the location of all the mixing valves. I think I saw one under the dash toward the center to the right of my gas pedal foot but I have no idea where any others are or how many of them there are. My guess is 2!

 

Might also consider flushing the heater core to the rear unit...

 

So you're saying there's 2 heater cores! I know there's one by the front passenger's feet. I assume that's the one for the front. Where is the one for the back located?

 

Look under the vehicle at the rear coroners and you should see where the rear heater hoses and AC lines run up to the rear system(s)

 

Ok. Thanks. I'll check that out. I found a diagram online of the box back there. It looks like it has the core and the mixing valve so I'll check them both while I'm there.