Help Diagnosing Air Compressor Failure

[HomeTheaterMan]

I have a Kobalt 80 Gallon 2 Stage air compressor that's failed. I don't remember the exact date I purchased it, but it's probably 4-5 years old so I hate to toss it out. It also serves my needs perfectly. I had absolutely 0 complaints until it died. This is a picture of an identical one to what I have. https://www.reddit.com/r/Autobody/comments/onqaix
Anyway, it just won't turn on. It doesn't start, doesn't attempt to start, doesn't make any noises, nothing. It's just completely dead. I got my mutli-meter out and started by checking that it had power coming into the switch which it does. The switch appears to be functioning properly and It also has power coming out of the switch where it goes into the electric motor when the switch is in the on position. I then moved on to the 2 capacitors. Both seem to test fine. On the start capacitor, when I switch my meter to capacitance mode and touch both terminals the reading shoots up then starts coming back down to zero. Just like it seems like it should. If I switch the meter to read uF it seems to be close. The capacitor is rated for 250+/- and I'm getting a reading of 292. When I test the run capacitor I'm getting similar results. Although as soon as I touch the terminals in capacitance mode it starts climbing and seems to continue. It doesn't stay at zero, which is what it seems like would happen if it's bad. When I switch it to uF mode and check, it's also pretty close to the spec.

While I don't have a ton of experience with bad capacitors, this leads me to believe they are both good.

I then spun the pully on the cast iron pump and it seems to spin normally. It's definitely not locked up. This leads me to believe the electric motor has failed. I tried the thermal reset button, but no luck there. Is there anything else I should be checking? Or is it safe to assume it's the electric motor at this point? It's fairly expensive so I don't want to just go tossing parts at it. I just want to make sure I'm not missing anything.

If it is, my options at this point seem to be to get one of the cheap VEVOR motors for $150 +/-. Spend $450 +/- for the original Campfield Hausfeld motor that's on there now. I'm not a fan of super cheap stuff. I'd rather spend more for it to last longer, but it doesn't seem like the original lasted very long anyway since it isn't that old and hasn't been used all that often. Or replace the whole air compressor. I'm really not sure that I want to put $450 into it at this point just to risk something else failing when I can get a similar spec Ingersoll Rand compressor for $1,350, but I'm truthfully not sure what to do at this point.

 

[seber]

I'm sure you did this already but just in case, have you removed the wiring cover on the motor and checked all the connections and wires?

 

[Shoreline_]

Sounds like a dead motor. Just buy whatever is in your budget. Just get one with similar current ratings.

 

[OccupantRJ]

As seber indicates you have more to check In the motor connections, along with resistance checks in the motor windings and checking the internal start switch. I found a textile thread across the contacts of one once. Initially it sounds like you have a broken or poor connection. Vibration can do this, and there is a lot of vibration on an air compressor.

 

[timgunn1962]

Unplug everything, switch your multimeter to resistance and check you've got continuity through the windings (both main and start) and also through the thermal overload.

You don't want to be swapping out a motor, even a cheapie, if it's just a faulty thermal overload or anything else that's cheap and easy to fix.



Caveat: I'm in the UK, where we use metric-frame motors and have 230VAC domestic power.

Personally, I'd stay well away from motors from Vevor or any of the other no-name cheapies. I'd be trying to find a local supplier of Techtop motors with a decent chance of support. We use quite a few motors at work and we've found the Techtops punch well above their weight: they are "proper" industrial motors and give me the impression that the Engineers have had the final say, rather than the beancounters. At work, where reliability is paramount and cost is less of a consideration, my first choices are Brook or ABB motors, with Techtop and a few others a little way behind.

Outside work, Techtop are pretty much the only motors I ever buy new. The only motors I buy used tend to be NEMA 56- or 56C-frame to fit machines that won't easily convert to metric motors. NEMA-sized motors tend to cost around twice as much as the IEC metric equivalents over here.

 

[HomeTheaterMan]

I'm sure you did this already but just in case, have you removed the wiring cover on the motor and checked all the connections and wires?

I did do that. Everything looks good there. I just didn't think to mention it in my earlier post.

 

[HomeTheaterMan]

Unplug everything, switch your multimeter to resistance and check you've got continuity through the windings (both main and start) and also through the thermal overload.

You don't want to be swapping out a motor, even a cheapie, if it's just a faulty thermal overload or anything else that's cheap and easy to fix.



Caveat: I'm in the UK, where we use metric-frame motors and have 230VAC domestic power.

Personally, I'd stay well away from motors from Vevor or any of the other no-name cheapies. I'd be trying to find a local supplier of Techtop motors with a decent chance of support. We use quite a few motors at work and we've found the Techtops punch well above their weight: they are "proper" industrial motors and give me the impression that the Engineers have had the final say, rather than the beancounters. At work, where reliability is paramount and cost is less of a consideration, my first choices are Brook or ABB motors, with Techtop and a few others a little way behind.

Outside work, Techtop are pretty much the only motors I ever buy new. The only motors I buy used tend to be NEMA 56- or 56C-frame to fit machines that won't easily convert to metric motors. NEMA-sized motors tend to cost around twice as much as the IEC metric equivalents over here.

Any idea what I should be looking for when I start checking the resistance? Having never taken one of these apart to check, I'm not sure what's normal. I'm also not really sure how to get it apart to he honest. I guess I'm going to have to fiddle with that. I popped the nuts off of the front and tried to pull the front off, but something else must be holding it together as it didn't budge.

 

[Shoreline_]

Any idea what I should be looking for when I start checking the resistance? Having never taken one of these apart to check, I'm not sure what's normal. I'm also not really sure how to get it apart to he honest. I guess I'm going to have to fiddle with that. I popped the nuts off of the front and tried to pull the front off, but something else must be holding it together as it didn't budge.

You can really only check a motor correctly with a megger or lcr. I dont know why people are telling you to check winding resistance with an ohm meter. Its not accurate unless you find an open winding.

 

[Firebrick43]

You can really only check a motor correctly with a megger or lcr. I dont know why people are telling you to check winding resistance with an ohm meter. Its not accurate unless you find an open winding.

You answered your own question, it’s a basic check that takes less than a min and if a winding is open why go any further?

 

[Shoreline_]

You answered your own question, it’s a basic check that takes less than a min and if a winding is open why go any further?

The op was asking how to check resistance with a meter. You cant measure winding resistance with an ohm meter. You can only check if the winding is open AKA not measuring resistance. You cant measure anything with an ohm meter. Do you understand? Measuring impedence of a coil is different than checking for an open coil.

People are telling him to check or measure resistance with an ohm meter. People arent saying "verify open coil with ohm meter"

 

[OccupantRJ]

Do you have an electric motor repair shop near you? They can tell you in a matter of minutes if you have a motor problem if you can remove and install the motor yourself. If so, label the wiring connections to aid reconnection. The end bells of motors are a tight fit and need to be bumped loose. Mark end bell relationship relative to motor center section beforehand.

 

[Firebrick43]

The op was asking how to check resistance with a meter. You cant measure winding resistance with an ohm meter. You can only check if the winding is open AKA not measuring resistance. You cant measure anything with an ohm meter. Do you understand? Measuring impedence of a coil is different than checking for an open coil.

People are telling him to check or measure resistance with an ohm meter. People arent saying "verify open coil with ohm meter"

Pedantry

You may not like how people worded it, but most of us understood what was being checked, and the check is performed with the meter to the Ω symbol to see if a winding is open or not. If a meter has continuity its still reading resistance and beeps at you if its below a threshold.

If it is open, you are absolutely are measuring resistance, it will read that its infinite

 

[gizardlizard]

I’m guessing it’s the thermal overload. That you can test with your meter, or jump it out for testing purposes. We see them fail at work far more than windings.

 

[gizardlizard]

Forgot to ask: is your pressure switch made? In other words, what does your psi gauge read? Maybe your compressor is at pressure already and the pressure switch is open.

 

[lbhsbz]

How to Test a Single Phase Motor?

A single-phase motor is tested using visual inspection, resistance testing, continuity testing, insulation resistance testing, & rotor checks. Follow safety measures and refer to the motor's manual for detailed instructions.

forumelectrical.com

 

[no704]

Also thinking pressure switch. You said the power switch appears to be working but are you actually getting power at the motor?

 

[gizardlizard]

Also thinking pressure switch. You said the power switch appears to be working but are you actually getting power at the motor?

Also thinking pressure switch. You said the power switch appears to be working but are you actually getting power at the motor?

Maybe he means the on/off switch but hasn’t actually checked the pressure switch. It could simply be at pressure.

 

[American Locomotive]

You mentioned you have power coming out of the switch. So the terminals leaving the switch going to the motor have 240v - correct?

If so, the next thing you need to do is unplug power, and then check the resistance of the motor at the switch terminals. You should have pretty low resistance, a couple 1-2 ohms, if that. If it shows open circuit, or something really high, like more than 50 ohms, something is wrong. Perhaps with the motor, or the connections going to the motor.

Next step after that would be to open the terminal cover on the motor, and check the resistance there. If it's still high or open, the problem is inside the motor.

If it does show as open even at the motor power terminals, I would suspect that the red thermal switch has failed.