Here we are cruising down the highway in the hot weather with the A/C on and all of a sudden it starts to kick into a heating mode; like that's what we need. There seems to be no reason for the change. One minute it's cool and the next it's blowing hot air. We shut the A/C down and then start it up again and it's OK for a for a few minutes. On other days, I can run it for a long time (an hour) with no problems. What's up? Thank you your imput.