Heating/cooling control

[plymouth71]

I am working on a 1971 plymouth scamp with a 225/6.The heat only blows through the front vents,will not change to floor or defrost.When I hit the heat or defrost buttons I can hear the system changing behind the dash but it always blows through the front vents.I have not worked on many heating/cooling systems,so any help would be welcomed.Thanks

 

[RedFish]

There are several vacuum operated servos that move the doors in the case. if you can hear the servo move but it doesn't redirect the air, linkage is disconnected so door isn't moving. If you're only hearing the controller buttons move the controller may be broken inside. Those push button controller were a common fault.
Get a factory service manual then remove the glovebox liner and the under dash vent assembly. You'll be able to see most of it.

 

[norshorblufish]

2x

 

[plymouth71]

There are several vacuum operated servos that move the doors in the case. if you can hear the servo move but it doesn't redirect the air, linkage is disconnected so door isn't moving. If you're only hearing the controller buttons move the controller may be broken inside. Those push button controller were a common fault.
Get a factory service manual then remove the glovebox liner and the under dash vent assembly. You'll be able to see most of it.

Thanks,I will try to find the problem.

 

[Oklacarcollecto]

Here is another possibility if you find nothing else. Look at this switch you will see a place where the vacumm hoses hook up on the back left side. These little ports get brittle and crack or break off. Some times the switch is just worn out.

View attachment $T2eC16V,!zUE9s38+CCeBRFCUEKh(!~~60_1.JPG

On this picture the ports are on the top right.

View attachment $T2eC16dHJG!E9nm3rIdEBRFVEGgdl!~~60_1.JPG

 

[plymouth71]

I would have never thought about checking the port connections.Thanks for the advice,I will check that also.

 

[BillGrissom]

On all my cars, I add a relay to the blower "High" wire so the full current doesn't route thru the switch. Otherwise, it will eventually melt both the switch and the pneumo-electric switch shown above. You may not have that switch if a factory non-AC car, as my 65 Dart is.