Update: I replaced both the run capacitor and the start capacitor and it did not help. Any ideas guys?
Original post below:
I have a 2005, 60 gal., single stage, 7ph (peak), belt drive, Sanborn air compressor which is wired directly to the breaker box by a short piece of romex wire. It has performed well for 16 years until recently, receiving regular but modest use. All parts are original. Model LA7006056.
In recent months it performed fine at start up but then the motor slows down and has a lower, labored sound when the pressure is roughly 60psi, although the compressor did still go to its usual maximum (120psi or so) but perhaps more slowly than when the compressor was newer. Then last Saturday, it began sounding labored when the pressure built up to 30psi or so, and did not go beyond about 70 psi, although it continued to run while sounding labored.
If I open the tank’s petcock at the bottom of the tank, it runs fine and continues pumping air into the tank (which then leaks out the open petcock).