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Air compressor not restarting

slow-poke said:
Usually the tolerance is written on the capacitor either in % or absolute.

The 177uF is interesting, Capacitors degrade to a lower value over time, so that's why I say interesting. Capacitors appear to be okay, assuming that 177 value is within the stated tolerance. Too high will cause increased start current.

If your centrifugal switch is dirty such that it is kicking out late that would cause over current briefly consistent with the overload trip.
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There is no tolerance stated on the 150mF capacitor, the smaller one has a +/- 6% tolerance.
The larger one is 27mF over or 18% which would seem to be out of any acceptable tolerance.
To eliminate temperature I can run it through a few cycles with the door open so the warm air doesn't build up.
 
David said:
There is no tolerance stated on the 150mF capacitor, the smaller one has a +/- 6% tolerance.
The larger one is 27mF over or 18% which would seem to be out of any acceptable tolerance.
To eliminate temperature I can run it through a few cycles with the door open so the warm air doesn't build up.
Click to expand...
The problem might be a combination of both. For the price of a replacement capacitor (that will likely fail long before the motor anyways), might be wise to get one.

When testing the new one or any capacitor for that matter make sure you discharge it just before you test it, and then test it both ways (reverse your test leads) you should get fairly consistent readings.

I'm paranoid about blowing up my meter when testing capacitors, that capacitor will hold whatever voltage (picture the sinewave where the peaks are +/- 340V) that was present when the power turned off, so it will hold some random voltage 0-340V and that's a meter killer.

If you set your meter to Voltage, discharge the capacitor and then measure the voltage it will be close to zero but not zero, if you wait a few minutes then measure again often the voltage will be a bit higher. That charge can effect your meter measurement.
 
David said:
I'll pick one up to rule it out as the issue
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It's a good idea David. I think the advice others have given is very good so I have refrained from "Piling on".

However, nobody has mentioned that meter accuracy for capacitance measurements isn't exactly stellar - even for premium meters. The meter tolerance can stack with the capacitor rating tolerance. To improve results, I always short out caps, remove both leads, and short again before measuring them. Only one lead is really necessary, but the extra step never hurts. Short them, remove leads, short again, then test.
 
Susquatch said:
It's a good idea David. I think the advice others have given is very good so I have refrained from "Piling on".

However, nobody has mentioned that meter accuracy for capacitance measurements isn't exactly stellar - even for premium meters. The meter tolerance can stack with the capacitor rating tolerance. To improve results, I always short out caps, remove both leads, and short again before measuring them. Only one lead is really necessary, but the extra step never hurts. Short them, remove leads, short again, then test.
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Yup that's pretty much what I did. I got three readings within .2 of each other.
 
Here's a data sheet on motor start capacitors. They don't give an ESR value so it probably doesn't matter.


But in either case here's from my ESR meter manual what to expect for DC capacitors. No idea if an AC motor start cap will have the same values.


1751212906281.png
 
Like everyone else who is following along I am interested in the outcome of what will ultimately solve the problem.

Just for clarity, as I don't believe it has been mentioned, the centrifugal switch should open within 2-3 seconds of start-up and remove the Start capacitor from the circuit.


@David this leads to a question because of something you mentioned earlier - I believe you said on at least one occasion you pushed the thermal overload reset button down with a little force and held it for a period of time so that the compressor was able to start?

If true, being that the bimetallic strip was already at operating temp. (open) is it possible it may have been slightly damaged? Maybe the contacts carbonized a little while forcing it down? I know you can't answer definitively without inspecting the switch but I thought it might be worth considering if some of the other troubleshooting steps don't result in a fix.
 
Elektrishun said:
Like everyone else who is following along I am interested in the outcome of what will ultimately solve the problem.

Just for clarity, as I don't believe it has been mentioned, the centrifugal switch should open within 2-3 seconds of start-up and remove the Start capacitor from the circuit.


@David this leads to a question because of something you mentioned earlier - I believe you said on at least one occasion you pushed the thermal overload reset button down with a little force and held it for a period of time so that the compressor was able to start?

If true, being that the bimetallic strip was already at operating temp. (open) is it possible it may have been slightly damaged? Maybe the contacts carbonized a little while forcing it down? I know you can't answer definitively without inspecting the switch but I thought it might be worth considering if some of the other troubleshooting steps don't result in a fix.
Click to expand...
That's a good point, to get at the switch I have to pull the end bell off the motor. I was hoping to avoid doing that but I may not be able too :(
 
Well I tried the compressor again today and it tripped at just over 100 psi with the door wide open. So something is very wrong with the thermal switch.
I tried to pull the end bell and there's no way I can get it off. Can't get a bearing puller in because there's no room for the arms and I'm afraid that cast aluminum end bell is going to break.
Tomorrow I'll pull the motor of the compressor and either take it to a shop or spring for a new one at Princess Auto for $229 :(
 
I hope you guys are off your asses and getting stuff done, it's not very often we get @David tripped up for this long!!!!! :rolleyes:
THIS IS OUR TIME TO RISE UP AND MAKE IT LOOK LIKE WE TOO CAN ACCOMPLISH!!!!! ;):cool:










If it's ok with you guys, I am just going to grab a cat nap, let me know how you make out. :p
 
I might poke my head in the garage even if I just replace the battery for the probe and center the table.
Who knows I might even put things back where they belong.
 
140mower said:
I hope you guys are off your asses and getting stuff done, it's not very often we get @David tripped up for this long!!!!! :rolleyes:
THIS IS OUR TIME TO RISE UP AND MAKE IT LOOK LIKE WE TOO CAN ACCOMPLISH!!!!! ;):cool:

If it's ok with you guys, I am just going to grab a cat nap, let me know how you make out. :p
Click to expand...
I'm innocent. I did not sabotage the @David compressor motor.

I was in Amsterdam trying to get a similar photo to a painting my parents brought over when they emigrated here.
1751242029295.png
 
140mower said:
I hope you guys are off your asses and getting stuff done, it's not very often we get @David tripped up for this long!!!!!
Click to expand...

Hey wait a minute! I happen to like my lazy ass way of not getting things done.




And just in case it matters, I'm taking a nap too!
 
I have taken a lot of motors apart, usually to replace bearings. I don't recall ever having a problem with an end cap not coming off. A gentle tap or two around the sides with your rubber mallet may help. And if you are really going to use a shotgun to kill this mosquito and buy a whole new motor then you have nothing to lose if you DO break the casting.
 
To late to edit my previous post but it sounds like it's either the starting cap, OR the centrifugal switch OR the bi-metallic overload switch. Or perhaps more than one of them, but any combination of those should be a lot less costly than a whole new motor.
 
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