First, a heat pump should have exactly the same cooling capacity as a
regular A/C unit of the same tonnage. You should really have your unit
serviced yearly to be sure it is working at maximum capacity and
efficiency. As to the breaker tripping, it is hard to diagnose without
being there, but from what you describe, it sounds more like a problem
in the electrical service to the unit rather than a problem with the
unit itself, but there are many possibilities, and unless you have some
basic experience with electrical work, it is best left to a pro. Your
best bet would be to call an A/C company, explain the problem to them,
and ask that they send an experienced service tech out. Most larger
companies will have techs with varying amounts of experience, and some
with more expertise in certain areas than others, so it wil be in their
best interest as well as yours to send someone out that can diagnose
your system rather than guess at it. Good luck, Larry