1973 Dodge Dart Sport No Heat.

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.