Heater Won't Blow on Windscreen

[Eggo]

Hi, please could someone give me some help/advice with the heater on my '73 Satellite? The air only comes out of the vents no matter what setting I have it on. When I turn it to vent or AC it comes out of the vents stronger, but when I have it set to DEF it only comes out of the vent and not on the windscreen. It blows hot air out of the vents when it's not moving but yesterday it was quite a cold day and the air it was blowing out of the vents was a bit on the cold side even though I had it set to warm.

I've never done something like this before as my other car doesn't really have a heater so am a bit confused about what to do. Do I need to take the dash off to get to it or will I be able to sort it out from underneath? Has anyone had anything similar happen and know why it might be doing this?

 

[moparmarks]

The problem is probably either in the switch or in the actuator from the heat/defroster door but I'm betting it is the switch since it is stuck on the vent mode. Unhook the vacuum hose going to the switch. You can do this at the motor. Then start the motor. Defrost is the default mode so it should be blowing out the defrost, windscreen.
It is fairly easy to pull the switch assy. out without pulling the dash.

 

[Red63440]

It almost sounds like you have two issues, one being the control of your heater doors and the other being the temperature of the air coming out. The temperature is controlled by the slide on your control panel which operates the heater valve, when you open or close the heater valve the this should change the flow of the water. So I would ask if your heater valve is opening when you slide the selector on your panel. If the answer is yes then you may have a blocked heater core, if the answer is no then your heater valve needs replaced OR the cable to your water control valve has broken.
The doors on your heater box are controlled by vacuum and if the doors aren’t opening then start by finding the vacuum line coming from the engine to the heater control. If you are able to access the actuators on your heater box and can manually move them while the car is running it’s normally a sign that there is no vacuum going to the doors or your control switch is faulty. I wish I could be more helpful on this but this will get you started.

 

[Eggo]

The problem is probably either in the switch or in the actuator from the heat/defroster door but I'm betting it is the switch since it is stuck on the vent mode. Unhook the vacuum hose going to the switch. You can do this at the motor. Then start the motor. Defrost is the default mode so it should be blowing out the defrost, windscreen.
It is fairly easy to pull the switch assy. out without pulling the dash.

Thank you! I'll have a look when I'm home, glad I probably won't need to take the dash out

 

[Eggo]

It almost sounds like you have two issues, one being the control of your heater doors and the other being the temperature of the air coming out. The temperature is controlled by the slide on your control panel which operates the heater valve, when you open or close the heater valve the this should change the flow of the water. So I would ask if your heater valve is opening when you slide the selector on your panel. If the answer is yes then you may have a blocked heater core, if the answer is no then your heater valve needs replaced OR the cable to your water control valve has broken.
The doors on your heater box are controlled by vacuum and if the doors aren’t opening then start by finding the vacuum line coming from the engine to the heater control. If you are able to access the actuators on your heater box and can manually move them while the car is running it’s normally a sign that there is no vacuum going to the doors or your control switch is faulty. I wish I could be more helpful on this but this will get you started.

This is super helpful, thank you! Will check these things later when Im home If the heater core is blocked is it something that can be easily unblocked or would it likely just need replacing?

 

[Red63440]

IF that is the problem it would need replaced but let’s hope it’s just the heater valve.

 

[Eggo]

IF that is the problem it would need replaced but let’s hope it’s just the heater valve.

I managed to sort it! wasn’t getting hotter because the switch cable for the heat wasn’t connected properly. the vacuum line was cracked as well so cut it off behind the break and it works so well now