How to determine what the winding resistance should be on a refrigerator compres

[Yamin]

Hi guys,
I've got a ice cream display which when the compressor turns on it trips the circuit breaker. I have ruled out loose connection etc. and it all points to the compressor.
What I have found is that the run capacitor which should be 20 uF is 14 uF and the Start relay contacts have arched and corroded away. I am going to replace both of those. (I changed the capacitor and tried the relay after cleaning and sanding down the contacts, still the C.B kept tripping).

Anyway going to my original question
I measured the coil resistance of the compressor and I get:
Common ---- Run = 1.5 ohms
Common  ---- Start = 5.4 ohms
Start ----- Run = 6.9 ohms

Does this look alright, 1.5 ohms seems low doesn't it? and I also checked whether the compressor was grounded and it wasn't.

Any help would be greatly appreciated.

[joseph nicholas]

Hi, You should be aware that compressors generally run hot when functioning normally.  The usual failure mode for these things is the thing just wears out and starts drawing more and more current.  I would check the current draw and compare it to the manufactures specifications as a place to start.  Hope this helps.

[Jeroen_Bezemer]

Check for isolation breakdown with a megger of at least 500V against ground/chassis

Verstuurd vanaf mijn ONEPLUS A6003 met Tapatalk

[Dacke]

There should be an LRA (lock rotor amps) number on the plate /sticker of the compressor,  this is current draw at start up.  It should reach close to this number when it starts then drop off very quickly to lower than RLA (run load amps).  You'd need an amp clamp to check this.   It's hard to tell anything by the resistance of the windings except that the order looks fine:  the lowest resistance will generally be between common and run with highest from start to run.

[bdunham7]

Hi guys,
I've got a ice cream display which when the compressor turns on it trips the circuit breaker. I have ruled out loose connection etc. and it all points to the compressor.
What I have found is that the run capacitor which should be 20 uF is 14 uF and the Start relay contacts have arched and corroded away. I am going to replace both of those. (I changed the capacitor and tried the relay after cleaning and sanding down the contacts, still the C.B kept tripping).

Anyway going to my original question
I measured the coil resistance of the compressor and I get:
Common ---- Run = 1.5 ohms
Common  ---- Start = 5.4 ohms
Start ----- Run = 6.9 ohms

Does this look alright, 1.5 ohms seems low doesn't it? and I also checked whether the compressor was grounded and it wasn't.

Any help would be greatly appreciated.

What size is this compressor--in terms of HP, kW or volts/amps?  And which 'circuit breaker' is tripping--the one in your electrical panel or the thermal cutout in the compressor?

[amyk]

Due to inductance, DC resistance will look a lot lower than the rated running current implies.

[Yamin]

Hi guys, just to give an update. I had a look at the data sheet of the compressor (NJ2212GK) and the resistance rating for the start winding is  7.25 ohms, the rated resistance value for the run winding is 1.95 ohms. So the readings I get are not 'so' off but there are a bit off. Could that be an issue.

I have replaced the starter relay and the run capacitor and still the breaker keeps tripping. The locked rotor value for the compressor is 36A, and the current MCB that was connected to it is rated at 10A. Just for the sake of it I tried a 32A MCB to see whether it was an issue with the MCB. Still it kept on tripping. I couldn't get enough time to even check the current draw.

Thanks

[amyk]

I would try this next:

Check for isolation breakdown with a megger of at least 500V against ground/chassis

Does the compressor actually try to turn, or is it stuck? In both cases it'll make a humming sound, but if it's stuck it'll sound like a loud transformer.