I have a 4 year old Lennox central air conditioner. It has run fine
until this summer.
Now after it has been running for about 15 minutes the circuit breaker
trips and the outside condensor fan stops. When running it does blow
cool air.

I have heard that it could be the compressor or something else with the
A/C unit or it could be a bad breaker. Since the unit is only 4 years
old I am thinking that it is unlikely that the compressor has gone bad.
If it were a bad breaker wouldn't it trip as soon as the unit turned
on?
Any thoughts?