Could it be the thermostat??

Question

When the heater on my Nissan is set at high and switched on with the re-circulating button depressed, the temperature needle drops from normal operating temp to cold within a few minutes. When the air flow is diverted to the windshield for defrosting with the heater still on high, the re-circulating button automatically deactivates bringing in all the bitterly cold air. I can’t seem to control the heat while defrosting the windshield at the same time. I use the same setting in my other car and it works fine – warm interior and clear windshield. Could this be a thermostat issue? Thanks.

Answer 1

Ok.
The reason the air gets colder with the defrost on is when you activate it, the A/C pump turns on to condesnse the water vapor in the air and reduce humidity to improve the defrosters performance.

The reason the "re-circulating" button deactivates is so that the humid air inside the car doesn't just blow around inside. Fresh air from outside is forced in to force out the humid air.

Now, as far as the air being cold, that's because the A/C is activated in this car and the engine may not have warmed up enough yet.
Your other car may not be set up the same. Same year,make and model?

Your thermostat is also probably stuck half closed.

Answer 2

If your temperature gauge is working ok, then I'd replace the engine coolant thermostat located under the little bell housing where the upper radiator hose connects to the top of the engine. Make sure to reinstall the new thermostat like the old one came out. To be sure of the proper replacement, I'd go to the dealer's parts department and buy the thermostat and gasket there.

Answer 3

Check your coolant level first. If the coolant level is full then it is your thermostat. Get a new one, they go for $5.....