Heater blowing cool then warm air

[belybutn]

2012 A7

just as the title says, blows hot air, then intermittenly will blow only warm air and continue going back and forth.

No issues with engine temp fluctuating and no visible leaks.

I'm assuming thermostat?

If so, I'd rather not pay the price quoted and just do it myself. Any good DIY for changing the thermostat?

Thanks!

[2k16A6]

The HVAC system adjusts the temperature of the air it outputs to maintain cabin temp at the setpoint. If the temperature changes are not extreme and the overall cabin temp (not directly in front of a vent) is fairly consistent, I'm guessing that's all you're noticing. If your fan is not on auto, then it could seem to change temp quite a bit from warm to cool as it's constantly reacting to temp changes due to the high volume of tempered air being introduced to the cabin.

If the temp difference is significant then it may be an issue with the HVAC system, potentially the thermostat for that system (not the thermostat for the engine coolant as you'd have different symptoms for that).

[belybutn]

Good insight thank you!

I did notice that it took longer for the engine to get to normal operating temp, and the outside temp was not extremely cold.

Know of any videos or threads for the HVAC thermostat?

[belybutn]

also, are you maybe talking about a heater control valve?