Q: The temperature gauge is at half way and the heater is blowing cold air with the heater on

The only purpose of the engine cooling system thermostat is to maintain optimal engine cooling system temperature, which is typically around 200 degrees. However, inasmuch as it is the engine coolant that provides the cabin heat (through the heater core in the dash), if the engine cooling system thermostat happened to be stuck open, causing engine coolant temperature to be below normal, you would definitely experience a reduction in cabin heat. But, you are reporting that the engine temperature is normal; consequently, the thermostat is not the cause of inadequate cabin heat in your circumstance.

Common causes of no cabin heat include malfunctioning blend door(s) (part of the in-dash ventilation network), a faulty or stuck heater control valve, a plugged heater core, stuck open engine cooling thermostat (not applicable in your case), collapsed hoses, and low coolant level. The cost to resolve the problem depends on which of the foregoing faults is the cause. If you desire a diagnostic to determine exactly why there is inadequate or no cabin heat, please request a non functioning cabin heater diagnostic and the responding mechanic will come right to your location and get this resolved for you promptly. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.