My 1999 Mercury Villager has the air conditioning compressor cycling on and off in heat mode with the temperature selector all the way up. The tubing from the compressor is sweating. The engine is over heating in the meantime. The radiator fan is cycling on and off but on only for seconds at a time. The top radiator hose is hot but so is the bottom radiator hose. When I sit with the car idleing it watching it to see what is happening it doesn't overheat, but if I am driving it does overheat. Anybody have any suggestions?