2000 T/C Rear Heater too hot

[donaldhall]

With heat needed, the rear heater blows fully HOT air. Fan speeds work OK. I know that the temperature setting for the rear heater is supposed to follow the driver's setting. How does it do that? I move the driver's temperature down until I am cold, but my rear passengers are still roasting. I opened the rear trim area, and found the blower and the cool/heat mode change damper, but there was no temperature control damper. (I know, the Haynes book did not say that there was one; I just assumed.) I opened up the dash to see if the driver temperature control damper connected to a mixing valve for the rear coolant. Nothing there, and I cannot see well enough between the engine and firewall. The Haynes book does mention a "High Temp Sensor" incorporated with the resistor which is inside (?) the rear blower motor. Is this some crude thermostat for the air? It is out of the circuit at high blower speed! I hate to buy a new rear blower if I don't need it, but I cannot figure out what else might be in control. My car-poolers (and I) will love you for a good lead on fixing this. Thanks!

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[Raptor 07]

The rear heater core is the source of heat for the rear system. Coolant is always flowing through it. The blower blows air through it heating the air that enters the cabin. The temperature is not regulated. The amount of hot air entering the cabin is. That is the mode doors' job. The mode door opening in proportion to the position of the drivers temperature slider switch is what determines the temperature of the air in the rear of the van by regulating the amount of hot air entering the cabin.

Remove the trim panel again. The end of the mode door shaft should be visible on the side of the HAVC unit facing the cabin at about the middle. Make sure it is rotating when you adjust the drivers temp slider switch.

Can you adjust the rear blower speed?

[donaldhall]

Well, I should have read before writing:

The owner's manual says, "Note: Only full heat or full cool is available for the rear system."
Dang, that is exactly what I am getting.

I remembered this much: Per the owner's manual, "Slide the [driver's] temperature control lever fully to the left for cold air from the headliner outlets, and [fully] to the right for heated air from the floor outlets. ... Once the rear 'temperature' has been set, the temperature control lever may now be adjusted for [driver] comfort."
When I had the trim open, I took the mode door actuator off the door shaft. It scared me because it would just run for a while, then stop in a random position. I opened the actuator, and found that it has no position feedback (I guess it is current limited, like a window regulator or door lock), so it does not modulate -- air either goes through the heater core and downward or through the evaporator coil and upward.

The blower speed can be adjusted OK, so there is no resistor problem.

I had my OBD unit (which also monitors real-time) plugged in a few days ago, and coolant temperature was wandering up around 210 or so, and that might be my problem -- the air is being heated more than it should be.

Thanks, Raptor, for the quick response!! Sorry I had neglected my homework before opening my mouth.

Don