1973 Dodge Dart Sport No Heat.

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lsrguy2007

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I have a 1973 Dodge Dart Sport. The engine heats up correctly. Both heater hoses get hot but no heat comes out of the vents when I use the slide switches to turn on the heat. Can anyone suggest what I can look for to solve the problem? Thank you.
 
Check cable connections on both ends to make sure they aren't disconnected first. Make sure heater blend door is working right.
Your heater core may be plugged/clogged up if all previous are working good.
 
I agree with above -if that is okay then try this:
If you relieve your radiator pressure at the radiator cap (engine cold) and clamp off your heater hoses remove them from the heater core ports at the firewall.
You can run water from a garden hose thru one side of the core and verify the core is not clogged internally. It should flow out the open side very easily. Put pressure to either side. Just put the hose end up to the pipe. This way you don’t over pressurize the core. Water pressure from the hose can be like upwards of 80psi and the core is built for 20psi or less.
Also- is the blower motor working?
Is air coming out but no heat- then the motor is working.

My guess is possible mouse nest blocking core. No easy repair for that one.
 
Syleng1 said:
I agree with above -if that is okay then try this:
If you relieve your radiator pressure at the radiator cap (engine cold) and clamp off your heater hoses remove them from the heater core ports at the firewall.
You can run water from a garden hose thru one side of the core and verify the core is not clogged internally. It should flow out the open side very easily. Put pressure to either side. Just put the hose end up to the pipe. This way you don’t over pressurize the core. Water pressure from the hose can be like upwards of 80psi and the core is built for 20psi or less.
Also- is the blower motor working?
Is air coming out but no heat- then the motor is working.

My guess is possible mouse nest blocking core. No easy repair for that one.
Click to expand...
Hi. I hear the blower motor working on both speeds. I do feel resistance when I slide the arm (I believe it's for temperature) over and it wants to slide back some. I'll check what you suggested. Thank you.
 
Pull the control panel to see if there is a vacuum switch on the back side.
 
@Syleng1 gives good advice. If water is flowing through the heater, core properly, which it sounds like it is since both heater hoses are getting hot, that will remove the heater core as a suspect. Then it comes down to some of the other suggestions, as for cables, or possibly a vacuum operated vent, that is not opening to allow air to flow across the heater core. I had a Dodge Caravan once that had poor heat. I back flushed the heater core with a garden hose, and then it worked OK after that. Have you used an IR thermometer at the thermostat housing to test the water temperature inside the engine?
 
lsrguy2007 said:
Hi. I hear the blower motor working on both speeds. I do feel resistance when I slide the arm (I believe it's for temperature) over and it wants to slide back some. I'll check what you suggested. Thank you.
Click to expand...

It’s not a big deal to pull the box and open it up to clean it out and verify blend door function.
I can have the whole heater unit out in about 15 minutes.
73’s don’t use vacuum controls. (Cables only)
 
Unless the core is blocked, doesn't the core have heat all of the time? Just a diverter to channel the air in or out? Not a big deal to pull and open the box up to see what may or not be in there. Had a big mouse house in the Road Runner I just bought, heater didn't work either.
 
harrisonm said:
@Syleng1 gives good advice. If water is flowing through the heater, core properly, which it sounds like it is since both heater hoses are getting hot, that will remove the heater core as a suspect. Then it comes down to some of the other suggestions, as for cables, or possibly a vacuum operated vent, that is not opening to allow air to flow across the heater core. I had a Dodge Caravan once that had poor heat. I back flushed the heater core with a garden hose, and then it worked OK after that. Have you used an IR thermometer at the thermostat housing to test the water temperature inside the engine?
Click to expand...
I have a temp gun so I'll check the temp. Never thought of doing that so thanks.
 
The heater core is a dirt trap. like most coils with only top connections for in and out. Reverse flush it with a garden hose. I have extra long heater hose for this. Disconnect at the core on the firewall, connect two longer hoses. I put one end in a 5 gal bucket to see how it looks, with the other end on the garden hose. Then swap and flush the other way.
 
73’s don’t use vacuum controls. (Cables only)
Click to expand...
Are you sure? I think AC car would have vacuum controlled vents and Non AC are cable only.
So is this car AC or Non-AC originally?
 
Checking the heater core with a garden hose is easy to do but for now let's assume that is not the issue.
Here is a list of possible problems.
Make sure there is vacuum at the hose connected to the heater control valve located under the hood on the right inner fender.
Bad vacuum actuator under dash or vacuum hose has come off one of the actuators.
Malfunctioning AC Heater control switch on dash.
Other members may have additional ideas.
 
If both heater hoses are getting hot there is flow through heater core. A partially clogged core will still warm both hoses but have marginal heat output. I would check and make sure there is vacuum connected to the dash controls. There should be a single line coming through the firewall that connects to a vacuum source.
 
The 1973 service manual can be found on MyMopar.
AC / HEAT vacuum circuit diagram for the Dart is on page 24-44. Explanation of the controls are also in Dart section.
 
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AC cars have a vacuum heater valve in the engine compartment. You can watch it move if you have someone else move the controls from heat to ac.
 
TrailBeast said:
Ah yes, I wasn’t thinking ac.
Sorry.
Click to expand...
Here's what I have under the hood and above the heater controls. It looks like a lot is missing.

IMG_20240121_112036782.jpg


IMG_20240121_112036782.jpg


IMG_20240121_112331461.jpg
 
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