Heater Control - Panel, Bi-level, Floor, Defrost

[keforbes]

I move the lower slider on the heater control but nothing happens, it stays on defrost with air blowing on the floor and windshield. Is there something electrical that makes the airflow change or is it controlled by a cable? Is there a schematic of the heater control? I can't find much in my Haynes Manual. I have a 1988 Dodge Aries without air conditioning.

[K-CAR_WAGON]

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[keforbes]

Thanks, I am betting whatever it is it happened at -40F this winter. There was one time in the extreme cold that I tried to move the slider and it was really stiff and I forced it to the defrost setting. Hopefully I didn't break something expensive. On the upside it is stuck at the defrost and floor setting because at least it will clear the windshield and heat the car in winter and cool the upper and lower level in the summer.

[niceold600]

not long ago i replaced my radio. after closing the dash back up i checked to see whether everything worked and was dismayed to find that my heater control only worked on defrost. thought i had broken something or left something disconnected.

it turns out that , as k-car wagon stated, air flow is vacuum controlled, and defrost is the default setting. i was testing without the engine running. started the engine and airflow was directed where i wanted it.

[keforbes]

I think the temperature control setting is controlled by a cable, but the the controls for airflow direction are vacuum controlled using vacuum with two vacuum actuators, and the control panel acts a control routing the vacuum differently as a function of the selected setting, thus controlling the actuators located at the doors. You could have bad vacuum hose, bad actuator, bad control panel or a stuck door.

Hey K-CAR_WAGON,
You were absolutely correct about the vacuum problem. The service person who replaced my brake master cylinder jambed the small vacuum line between the master cylinder and the brake booster. It is all better now after the vacuum line was removed and repaired.
Thank you for the help.

[aussiewoody]

Great outcome from this thread and a lesson for us all - thanks