heater stops putting out heat at a stop blows cold on 1995 Mercury Villager

the heater stops putting out heat at a stop, blows cold air, once car start moving blow hot again. I have ck coolant and overflow was low added drove still doing it will check once car is cooled down but was wondering what else to ck

Asked by for the 1995 Mercury Villager
Check that coolant level to be sure it is full. If you find it low again on your 1995 Mercury Villager be sure to have your cooling system checked for leaks. For additional information on possible heater issues please see the following RepairPal article -