AC/Heater acting up

[Gruntwify]

Hi everyone, I have a 2002 QX4. My heater/ac was acting up and the dealer had my vehicle for 3 weeks because they couldn't figure out why it was acting up. They changed the temp sensors, the thermostats, gaskets, which we thought it was finally fixed...but nope, its doing it again. My heat won't come on until I turn the knob to 85..not 84..but 85. SO the air that blows on the top vents is still cold, but on my feet vent it changes they way it should. A couple of times too, it was backwards, my ac wouldn't turn on until I turn it to 65...but mostly it's the heat that acts up. And then also, this problem it's not constant, it comes and goes at it pleases. The dealer is as perplexed as I am and are very determined to fix it and are very nice about the whole thing, but it's just getting frustating not knowing what's wrong. Any suggestions? I have to drop it off again on Tuesday.

[Towncivilian]

See this thread and run the diagnostic procedure detailed on page HA-43 of the factory service manual.

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