919-175250 Replaced pressure switch, still not cutting out

by Jed
(Ohio)

Late 80’s sears/craftsman 60 gallon 5hp compressor. Model 919175250. Just replaced the original pressure switch with a new square d unit, set with cut in at 95 and cut out at 125. Compressor builds pressure fine, just doesn’t shut off at set pressure. Continues to run till pressure relief kicks in and releases pressure which shuts the compressor down till it drops below 95 psi, the it kicks back on and repeats the process.

Comments for 919-175250 Replaced pressure switch, still not cutting out

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Jul 13, 2018
919-175250 pressure switch
by: Doug in s.d.ca

"set with cut in at 95 and cut out at 125"

How do you know? Factory set?

"Continues to run till pressure relief kicks in and releases pressure which shuts the compressor down till it drops below 95 psi"

What pressure is that?

You say it blows the safety and shuts off at the same time?

Sounds like you might just need to tweak the cut-out a bit lower, or maybe replace the PRV.


Jul 13, 2018
919-175250
by: Bill

Well Jed, as I expect you know, the pressure switch reacts to pressure.

When the tank pressure falls to below the cut in pressure setting, the contacts in the switch close, and stay closed, allowing the compressor motor and pump to run until the tank pressure reaches the cut out pressure setting, at which point the points open, power stops flowing to the motor, and the pump stops.

Now, if the cut in on your switch is 95 PSI, it seems clear that the switch contacts are closing at that point, to allow the motor to start.

Or, are we sure? Is it possible the contacts have welded shut for some reason, and if that were the case, they could not open to cut the power.

It is clear that power is flowing through the switch to the motor at all pressures.

What may be more likely is that, when wiring the switch, the wires were attached to terminals where the power flows all the time? Did you recheck to ensure that wires were all connected correctly?

Last thought, if the wires are right, and the contacts are not welded together and they open and close, then the only other logical conclusion is that the new switch is pooched.

Also, if the set point is 125 PSI, the contacts should open when tank pressure reaches that pressure, unless, for some reason, the switch is not "seeing" the tank pressure, and then it won't shut off at all once the motor starts.

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