According to Trane, my heat pump's high pressure switch will trip
during power surges. We've had a few during the past few weeks. So it
seems that was what caused the problem. This is based on it not
recurring since I shut the system down last week for a few minutes and
restarted it. Thanks to all who replied... but... it sure would be
nice if some knowledgeable person would just answer my original
question regarding the location of the high pressure switch (without
the "sales" pitch or warnings of doom, etc...).