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Before we talk about how to buy a compressor motor reset switch, what are the compressor symptoms that would lead someone to have to buy one? Here’s a typical scenario. The compressor has been running well for some time as air tool is being used. This air tool has been used quite a bit, and the compressor, up until this point, has had no problem keeping up with the air demand and is able to shut off with a full tank from time to time to allow the motor to cool.
All of a sudden and right in the middle of the compressor running to rebuild the air in the tank another time the compressor stops.
That the compressor has stopped may go unnoticed for a while as the air tool is running and that’s making a bunch of noise but then, the air tool slowly winds down and stops even though the trigger is being pulled. There is no air coming out of the air tool exhaust, meaning there is no air going into the air tool. The regulator gauge is reading zero PSI. The tank gauge is reading zero PSI. Now that the air tool is silent it’s clear that the compressor is no longer running.
A quick check shows there is power at the plug, and a meter reading at the pressure switch shows that power is flowing through the switch to the motor wires.
All of a sudden the compressor bursts into life. The tank pressure builds to the stopping point and the air compressor stops. Air tool work is undertaken once again. The air compressor cycles normally for some time, the air usage of it isn’t overwhelming in terms of running the compressor too long at one time, but once again, the compressor stops mid-fill for no apparent reason.
Resetting the compressor motor switch!
Then, pushing the air compressor reset switch on the motor brings the motor and compressor back to life. Not quite sure about where the reset is? This page will help.
This happens again and again. The compressor motor is not overheating but the reset switch just shuts the motor off from time to time and apparently randomly.
While there are many circumstances that might cause this, things like poor power supply, too long compressor use between motor cool downs, motor capacitor issues and a failing reset button could be the cause.
“A motor subjected to overloading due to very long duty on-cycles may run hot and trip the thermal overload protection device. Eventually the thermal overload switch may itself fail and the motor will no longer restart nor can you reset the thermal overload switch.” (Source: https://inspectapedia.com/electric/Motor_Reset_Button.php)
There are a number of pages on this site that deal with the other issues that may cause the compressor to cut out from time to time and if not one of them, the motor reset button may need replacing. This page is about doing just that and how to buy a replacement compressor motor reset switch for that compressor motor, a not too easy process, unfortunately.
“Insulation class (INSUL CLASS) is an expression of the standard classification of the thermal tolerance of the motor winding. Insulation class is a letter designation such as “B” or “F”, depending on the winding’s ability to survive a given operating temperature for a given life. The farther in the alphabet, the better the performance. For instance, a class “F” insulation has a longer nominal life at a given operating temperature than a class “B”.” (Source: electrical-engineering-portal.com)
Bypass the compressor motor reset?
Is it possible to bypass the thermal cut out on the compressor motor? Sure you can, and this could be a good diagnostic tool to determine if it is the thermal reset switch that’s the problem.
Typically there’s one wire into the thermal reset switch, and one wire out. It’s the same wire essentially that’s get connected and disconnected by the condition of the switch. Power passes if the temperature isn’t too hot, but when the temp gets too high, the switch opens and power stops flowing to the motor.
Connect the in and the out wires together bypassing the switch, and run the compressor up to cut out. Dump all the air to cut and and let it run up again. Wait five minutes, and do it again twice. If the compressor runs up to cut out each time with no problem, odds are improving that it is the cut out that’s at fault.
Don’t leave the thermal cut out bypassed. The underlying reason for the failure, if it is not just the switch itself, may not get resolved and could lead to motor failure due to overheating.
So, how to buy a compressor motor reset switch?
I expect the motor owner may need to get creative. By that I mean that the compressor store won’t have a motor reset button, the motor manufacturer may have one but odds seem to be that their solution is to sell a whole new motor rather than just the switch. We do seem to be morphing into a throw-away-rather-than-fix society, haven’t we?
If there is an electric motor repair shop anywhere accessible they may have the one for the compressor motor, particularly if it’s a brand name (not likely if the compressor is made offshore) or they may be able to use a reset switch from another motor on the compressor motor needing the switch.
DIY compressor motor reset replacement
Or, it’s possible to get creative and chase down a switch that suits and replace it as a DIY project.
First consider what switch is being looked for. It is a reset switch that has the protection setting similar to that of the motor on the compressor, and one that is similar in size so that it can be fit inside the motor housing on the existing compressor motor.
To get some idea of that, try to locate the motor information plate, usually found on the outer casing of the motor. Check for the motor class if that info is shown. If not, it may have an upper temperature number shown on the info plate.
No luck? Check the motor HP and visit the local compressor store. Have a look at motors of the same HP and similar sized pumps. Check the motor info plate. No guarantee of course, but odds are pretty good that a similar sized motor and a compressor with the similar sized pump will have the same temperature protection. Just don’t default to a larger HP motor as they will likely have higher thermal cut outs than a smaller HP compressor motor.
Google ‘buy an electric compressor motor reset ‘ or ‘buy replacement resettable thermal circuit breaker”to start the search. You’ll find many offshore suppliers as I did, but drill deeper with other terms. There are North American suppliers, as I’ve found them following these guidelines.
Compressor reset reality
The reality is that at present, the compressor isn’t working, correct?
The thermal reset switch has been determined to be at fault, and a replacement may be acquired for a fairly small cost as compared to the cost of a new motor which includes a new reset.
Finding the correct thermal circuit breaker for a specific motor is difficult.
If the only other option then is to buy a new motor (or junk the compressor and buy a new one if the original compressor cost was low enough) what have you got to lose to try and replace the reset switch with an off brand? It is possible that the compressor motor eventually fries and then you’re back to buying a new motor anyhow.
Good luck with the project and maybe let us know your effort and result?
If how to size a motor pulley, we have a guide with a worked example on our site!