The Carrier heat pump / air conditioning unit (model 38YMA036300)
installed on a 2700 sq ft house 15 years ago has stopped cooling. On
the unit outside, the fan is blowing and the compressor is working,
but the air after the radiator is not warm/hot. The copper pipe coming
out of the compressor is hot and remains hot going into two parts of
radiator, but none of the other copper U elbows feel hot or even warm.
It seems the radiator is clogged. Is there a simply way to further
verify that this is the problem?

Should I have the outside unit repaired or replace the entire system?
Which brand provides a good value and above average reliability? Thx