Does a broken thermostat cause the defroster inside your car to put frost on your inside window instead of remove it?

If the defroster is blowing hot air and it is still leaving moisture on the inside of the windshield, the heater core may be leaking coolant causing that condition. If the defroster is blowing cold air it could be the cooling system is low on coolant, or the thermostat is stuck open or the heater core is plugged up or the temp blend door has a malfunction.