Hi,
This sounds like a blend door or air mix door issue. The way this works is, the air is ALWAYS directed over the AC evaporator when it is taken in from the fresh air vent. When the AC is on, the air is cooled and conditioned (moisture removed) and then distributed through the cabin. When you turn the heat on, the air still comes over the evaporator but the blend door moves and directs the air over the heater core to warm the air prior to it coming into the cabin.
If this were low on freon then they would find that because that would not be intermittent. Also, the fact that this happens sometimes but not others points to an issue like this where the blend door just opens and allows air in to be heated over the heater core and then when you shut it off, it resets itself.
The other thing it possibly could be is the compressor clutch intermittently does not engage. This can happen as the clutch wears out. This is easy to verify so next time this does it and it is blowing warm, open the hood and see if the compressor clutch is spinning. It should cycle on and off so just listen for a couple minutes and see that it comes on and off. I included a video of a compressor clutch cycling so you can see what it looks like. Your's may be in a different position on the engine but the front part that spins will look similar.
Disregard the topic they are talking about because that does not apply to you. I just want you to see the clutch in the background at the 30 second mark of the video.
https://youtu.be/XAlw_aoaPF8
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Wednesday, May 1st, 2019 AT 6:45 PM
