Make repairs to an older Sears Air Compressor
I am trying to clean up and make repairs to an older Sears Air Compressor (model # 919.174320).
The handle is broken, the electrical cord frayed, etc.
I have purchased parts from Sears.com but the pressure switch is no longer available. I suspect that this switch has been replaced in the past as it has a square D switch which I doubt came on a Sears Compressor.
The switch has two sets of contact points of which one set is broken off and has been glued on. The glue failed and I would like to replace the switch.
I can't find a p/n on the Square D switch. This switch has an on/off lever and what I suspect is an "unloader" feature. By this, I mean that the switch has a seperate small aluminum tube attached from the compressor cyl. head. The actual switch sits atop a nipple from the storage tank but the smaller tube comes from the compressor head.
I can purchase from Grainger if I just can figure out what part number I need. Your help would be appreciated.
You are quite correct that most DIY type compressor pressure switches incorporate the unloader valve as part of their design and the line from compressor head is attached to the unloader valve in the pressure switch.
I have uploaded a picture to show how the pressure switch toggles a small valve at the end of the "tube from the compressor head" on my home compressor, thus allowing air trapped over the piston to escape when
the pressure switch toggles to off and that process depresses the pin on the valve.
I can't be sure what model or part number of pressure switch will suit your compressor best.
I am fairly sure that any "standard" compressor pressure switch will work, though I appreciate it's hard to buy one on-line, as you can't easily send it back if it doesn't work.
Here is one that should. The photo is a link.
You may have to finagle with the line from the compressor head to fit into the fitting under the switch, shown on the left.
The male thread (center bottom) will thread into the nipple from your tank. You might need a bushing to allow you to join two male threads, since as you can see, the pressure switch has a male thread for attaching to the tank fitting.
The pressure switch will have two adjusting nuts on springs inside it to allow you to set the cut in and cut out pressures. Though I don't recommend that DIY folks mess with the settings, you may have to adjust your new switch.
The paperwork that comes with the switch should tell you the existing settings, or, look inside the cover for that info.
Or, once you've installed it, plug in the compressor and see what the existing pressure settings are. You probably want to set them, if they aren't set there already, to 85 PSI cut-in and 125 PSI cut-out.
This presupposes that the components are sound and can handle this (what are normal settings)pressure.
Sears compressor wont shut off even after PRV releases.
by Gary K
Sears 100 PSI compressor wont shut off even after PRV releases.
I replaced the pressure switch and it still does the same thing. Today I found the valve spring in regulator was rusted to zilch.
Could this be the problem? If so, where can I find one?
Gary, when the compressor was working properly, what was the cut in pressure and what was the cut out pressure settings? What pressure is the PRV releasing at?
The pressure switch is what controls the on/off of the compressor, switching it on when the pressure drops below cut in, and turning the air compressor off when the pressure reaches cut out.
If the compressor never reaches the cut out pressure level, it will run and run to overheat and self destruction is a possibility.
If the air compressor tank pressure exceeds the cut out setting of the pressure switch, then the pressure switch has failed.
If the PRV is letting go before the tank pressure reaches cut out, then it's the PRV that is suspect.
Regardless, the regulator spring has no control over the start/stop of your compressor, though you will be hard pressed to set your downstream pressure with that regulator, if the spring is pooched.
If the new pressure switch is emulating the old, and you have installed the new one correctly, then let me know the pressure specs as I noted above as a comment here.