My 2009 Ford Explorer Eddie Bauer has a strange heater issue. It is not an issue with the door. With the engine off but key turned on I can switch the temperature control from cold to hot and hear the door switch positions. Once the engine warms up if the fan speed is on the lowest setting I can feel warm air coming out of the defrost. If I increase the air speed the first burst of air is warm but it quickly turns cold. I seems as if there is a low flow of coolant circulating through the heater core. The air flow quickly dissipates the heater from the heater core quicker than the coolant flow can reheat it. I don't know if I have a vapor lock or what. that is the only thing I can think. of. Does anyone have any ideas? If it is a vapor lock, how do I clear it to get the coolant flowing again?