Came home to find the upstairs unit which was set to cool instead
putting out heat; the thermometer read 99 (but took hours to change to
98, so i think it was much higher). by the time the repairman came, it
worked fine. he checked the reversing valve and said it was fine, must
be the thermostat. i am skeptical; we have had ants foul the solenoid
on another unit.
any way for a layman to check this out?