Pontiac Repair: 2001 Pontiac Montana Rear Heater Stuck On, pontiac montana, hot position

Question
I have a 2001 Pontiac Montana with the rear heater is stuck on. The water lines are hot like water is flowing through them even though I have the temperature gauge set to cold. The temperature control works at the front dash for the front heater core. But the controls that are on the ceiling just behind the front seats don't seem to make any difference for the rear heater core. In the summer when I run the AC it is blowing hot air for the rear occupants. I pulled off the side cover and I can feel the rear AC is getting cold, but the heater core is stuck on. I'm wondering where is the actual valve that shuts off the flow of water to the rear heater core and is there an electronic controller that actuates the valve for the rear heater?

Thanks for any help you can provide, especially so I don't have to hear my kids complain about it being so hot in the rear of the van.

Answer
Hey Sean:

The rear heater unit on that van the hot water runs to the rear unit all the time. On some of the newer vans there is a pump in the rear lines but the coolant still flows through the lines the pump just increases the water flow to it will not loose the heat from front to rear that pump if equipped is mounted just above air cleaner assembly on the left side of the engine compartment you can unplug it is equipped and it will slow the heating down. I think what you have going on here is the temperature door in the rear air distribution is either stuck, or the actuator is stuck in the hot position or the control head for the rear unit is bad and is commanding the rear heat door on all the time. It's one of the three possibilities. with out seeing it. Good luck :)