I have a customer who has a vertical pie display cooler. It is an older unit from 1988, originally had r-12 in it, time clock has 409a wrote on it. The complaint was the cooler will work fine for a few days, then it will run around 60 box temp, customer leaves the cooler off overnight and starts it the next day and it seems ok for a day. I noticed everything seems to be original except for the fact someone replaced the start components. My customer has only had the cooler for about 6 months, bought it used at an equipment auction. The unit had been off for 2 weeks when I worked on it, started it up, it pulled down to 34 or so and cycled off quite quickly, was off a few min and cycled back on from the pressure switch, pulled back down to temp and cycled off, everything was working fine until the 3d time it tried to cycle on, the compressor tried to start but tripped the o.l. as soon as the o.l. reset it started fine. The customer had the cut in set at 25#, diff was at 10#. I set the cut in at 35# and increased the differential to 20#. This helped the compressor have more off time and I thought it would be ok but the last time it cycled on it again tripped the o.l. The start cap tests fine, electrical all is ok, I can make the compressor fail to start very intermittently by cycling the power switch on/off, the compressor will start right back up most if i shut it off then right back on with no delay, other times if i leave the power off several min. the compressor will fail. I believe the compressor is just wore out and if it stops in the right position it fails mechanically to move and tripps the o.l. I thought about a larger start cap or a time delay relay but even if it makes it run ok now I think it is just a matter of time before it fails completely. Any other ideas that I may have over looked??