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It starts and runs, but sounds a lot quieter than it did, and only pumps to 20psi, and shuts off. It also sounds funny. Like an echo, hollow-type sound. First thought, of course, was the pressure switch, that shuts it off was bad, but the running quiet, and sounding funny throws me off. Any ideas are greatly appreciated.
Mark, there are a number of reasons why an air compressor will not build pressure, and why an air compressor will shut off before the tank pressure reaches the normal cut out.
The sound change suggests to me a valve and/or gasket problem.
But, the compressor should not shut off at 20 PSI, even if that’s all the pressure the pump can generate, unless, of course, it’s running so long it overheats and goes off on the compressor tripping thermal overload.
If the compressor shuts off at 20 PSI and the pump and motor are fairly cool, as in only running a few minutes, you need to have a look at the pressure switch innards to see if the pressure switch has tripped off. If it has tripped off at 20 PSI, then I would suspect the switch itself is the issue.
Other reasons why a compressor will not build pressure are covered on pages linked from the troubleshooting page. Help yourself and please tell us what you found.