Chrysler Repair: 94 Chrysler LHS Heater Control Issue

Question
Hello,  I am working on a 94 Chrysler LHS which has the temperature control system (set a temp and the car tries to match it.  Unfortunately it is always blowing hot air.  I am assuming the heater control valve is stuck open.  But, wont know that until I can find the valve.  (I have looked under the hood and tried to follow the heater lines visually and have not seen any valve.  Can you tell me where the valve is and if there is anything else I should be looking at?

Thank you,

Bud

Answer
Hi Bud,
There is no hearer valve proper. Rather the unit has a door which sends the air across either the heater core or the ac evaporator core or a mix of the two pathways in accordance with the temperature you have requested.
Chances are that mode door is stuck or the electrically-controlled actuator that moves the door to the requested position no longer working. Fortunately the actuator is on the underside of the unit above the floor tunnel, toward the firewall. The control unit has self-diagnostic capability to verify which is the issue. With the engine running but the car not moving. Place the temp request at 75F. Then simultaneously press and hold the floor, mix, and defrost buttons (first, second and fourth on the top row). The panel will begin blink shortly thereafter, then release the buttons simultaneously and the self-test begins. At the conclusion either the panel will return to 75F (indicating no faults detected) or a two digit number will appear. To see if there is another fault number than the one shown press the panel button (first from the left on the bottom row). The fault codes range from 23 to 36. They can be erased by disconnecting the battery for 10 minutes.
Let me know what you find and we'll go from there.
Roland