3rd Gen Blend Door

So I'm driving on the highway with the temp on cool, not A/C, had adjusted the temp a few times, and I feel hot air suddenly out of he vents. It goes cool again after a few seconds. This happens a few times over a five hour drive. Not related I think, but it seems it happened when down shifting going up a hills. No change on the temp gauge. Plus the temp swung quickly so I suspect it was not a thermostat issue.

I opened a case with Toyota hoping they may help me out since my 8 yr extended ran out just a couple weeks ago - Lucky Me. Anybody have any experience with this ?

Thanks

 

To clarify the AC compressor isn't on and the vents will periodically blow warmer than ambient air after the truck has downshifted to climb a hill?

 

Yes or shortly after shifting back up.

 

Sounds normal. Without the AC on the vents are simply blowing out whatever air is or isn't passing through the heater core. More heat occurs from the engine doing more work which gets translated to the un air conditioned vents.