Reader Question I have a 1989 Plymouth Voyager SE that is having issues with heat. The radiator works fine and the thermostat appears to be working as well since all of the hoses are hot.
The heater core is not leaking so we are assuming that it is ok. We have lukewarm heat but it is not quite enough to keep the windows clear of ice. The air conditioning motor keeps coming on and my father in-law is thinking that it shouldn’t be but since we just got the vehicle we are not sure.
It sounds like you might have a “dash control head” problem if you have both heater hoses hot but the a/c compressor is coming on and off. Make sure you have the dash controls set correctly and that the heater is selected and the a/c compressor button is off. There is a heater control valve under the hood on the passenger side located on one of the heater hoses leading inside the cab of the vehicle.
The job of the heater control valve is to open a valve inside the hose and allow hot coolant to enter the heater core inside the dash of the vehicle. Make sure that BOTH heater hoses are hot after the heater control valve. If both heater hoses are hot, you probably have a problem inside the dash or a switching problem with the dash controls. If the radiator is low on coolant…you won’t get heat, so check the water level inside the radiator.
If the 2 heater hoses are not HOT…neither will be the heater. Since you do have luke warm heat, I would assume some hot water is making its way to the heater core so you either don’t have enough water (low coolant level in the radiator) , the heater core is full of rust not allowing proper flow of hot water thru it ( one heater hose will feel much cooler than the other heater hose) or there is a dash/control problem.