Hi, I don't know much about this subject, so please bear with me...I am
visiting from college, and just found out my mom had a problem with her
heat pump.

The heat pump will no longer shut off. The fan control at the
thermostat works, but no matter what, the outside unit continues to
run.

She switched the circuit breaker off upon realizing the problem.

The unit is 20 years old. If it matters at all, the unit is branded
"Payne high efficience heat pump", and is white/off-white with a green
grill. Again, if it matters, her house is a 20-yr. old double-wide
mobile home.

It was last serviced in June of '05. The service was to top off the
coolant, and "check it over", at least in theory.

She lives about 30 minutes from town, so I assume a service call would
be somewhat expensive for her. Should she call for a repair or would it
make more sense to just go for a replacement at this point? Thanks,

Note: Sorry for the double-post, I initially put this in the alt.hvac
forum, until it was suggested I move it here.