Nissan Quest Mystiry

On long trips in the hot summer, our Nissan Quest, 1997 V6, will shut down but restore itself within 20 minutes–and keep running if I am careful not to use the air conditioning. The dealer put it on the machine, but could not find the cause. What is going on?

There’s not enough info known to make much of a guess. However, I would advise that you get someone else to scan the vehicle to see if any codes are present.
Car parts houses such as AutoZone, O’Reillys, Checkers, etc. will do this for you free and it only takes a few minutes.
Just consider this a backup test.

Shutting down due to heat could be caused by any number of things; ignition system, ignition switch, or even a fuel pump.
Question though. When the A/C is in operation are the radiator cooling fans working?

I don’t know–but the heat guage doesn’t show the motor overheating. It stays at about 1/3 at the cold end–even if the weather is hot. SH