Intermittent heat?

Hi,

Is the engine coolant full? Also, there are temperature sensors in the HVAC duct. The air temperature sensors are 2-wire negative temperature co-efficient thermistors. The sensors are installed in the air distribution ducts and measure the temperature of the air that streams from the ducts. The HVAC control module uses these values to adjust the mixed air flap position according to the requested temperature.

So, if all vents are changing temperature at the same time, my first suspect is the HVAC control module. See the pic below showing temperature sensors. However, if there is a failure, they should have found it by scanning the can-bus. Do you know if that was done?

You also indicated they checked the cycling of the doors. I suspect that means the blend air doors that control temperature. If they were checked with the heat on high, they never should have moved. However, for the temperature to cool, they had to unless there is a partial blockage in the heater core itself.

Let me know your thoughts and as much as you can.

Take care,

Joe

See pic below.

Hi,

Thanks for the update. I have a feeling it is the HVAC module that has an intermittent fault causing it. If it was only one vent, I would think more on the line of a sensor issue.

Let me know what they tell you.

Take care,

Joe