I have a 2000 Dodge Neon with 70,000 miles. The heater controls have 3 dials; one controls the fan speed, one controls the air ouput (i.E. Floor, dash, front window) and the third selects vent or re-circ. Once the engine warms up, I will have I will select re-circ mode coming through the dash. The air is hot. If I change to defrost (front window) it will automatically change to vent and the air will rapidly cool. After further testing, anytime I have the third dial set to vent, there is a large drop in temperature as compared to re-circ. I took it to my local dealer who promptly diagnosed thermostat. I had the thermostat replaced with no change in symptoms. A different technician looked at my car and says its probably my water pump. I don't see how either one of those is a correct diagnosis. If my thermostat was stuck closed as first stated, wouldn't my engine temp rise rapidly? Same thing with the water pump? The temperature gauge on the dash does not show an abnormal condition. In fact, it now looks as if it is lower than usual.