Author Topic: How do you check a compressor to see if it is good?  (Read 9085 times)

Offline moderators night

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How do you check a compressor to see if it is good?
« on: May 16, 2009, 09:46:25 PM »
This one isn't on the recall list per Maytag today. I'm pretty sure that the relay is bad (rattles), but before I buy a relay, I'd like to be sure that this compressor is good. Should you have continuity or not? I checked it with one meter, and it zeroed out. Then I checked it with a better meter, and it zeroed out, then gained some.
Anyway, how do you check it correctly?
Thank you!

Model MSD2456DEW

Offline jumptrout51

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Re: How do you check a compressor to see if it is good?
« Reply #1 on: May 17, 2009, 05:17:10 AM »
CSR...Can She Run.
With a meter set for continuity Check each pin to the compressor dome. Any reading the compressor is shorted out. Check each pin to the other and record the number.C to S and Cto R should equal S to R.
CSR...Common,Start,Run.
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Offline Repair-man

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Re: How do you check a compressor to see if it is good?
« Reply #2 on: May 17, 2009, 05:18:18 AM »
Here's a little insight about compressors....you can check the resistance of the windings all day long (until the cows come home), but even a compressor that shows good resistance on the windings can have a locked rotor. Only by installing a new relay/overload can you measure the run load amperage of the compressor while it is starting up.  There is no way around this.

Go ahead and invest in a relay or a 3 in 1 start kit.

Overload and relay for your model- part # 12002783
« Last Edit: May 17, 2009, 05:20:31 AM by Repair-man »
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Offline RegUS_PatOff

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Re: How do you check a compressor to see if it is good?
« Reply #3 on: May 17, 2009, 08:55:15 AM »
 :coffee:

attachment:
« Last Edit: May 27, 2009, 04:09:20 PM by RegUS_PatOff »
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Offline JWWebster

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Re: How do you check a compressor to see if it is good?
« Reply #4 on: May 17, 2009, 07:37:52 PM »
I actually have one of those cords,that is old school.
I use a Hard start.
« Last Edit: May 17, 2009, 08:36:07 PM by JWWebster »
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Offline MajorApp

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Re: How do you check a compressor to see if it is good?
« Reply #5 on: May 17, 2009, 08:27:18 PM »
 Are they for sale somewhere or do you have to make one?

Offline JWWebster

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Re: How do you check a compressor to see if it is good?
« Reply #6 on: May 17, 2009, 08:37:39 PM »
Mine I will have to dig up and see but I believe it is made by gemline
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About the icons: The beer is tip link, if a tech saves ya some money buy em a 6 pack. The small green square=personal message. The green dot is a link to my web page on appliance repair and other general BS I love to post. The letter sends me email.
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Offline JWWebster

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Re: How do you check a compressor to see if it is good?
« Reply #7 on: May 17, 2009, 08:43:35 PM »
You would be better off to buy  hardstart and attach a lamp cord to it to check compressors.
May the hinges of our friendship
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About the icons: The beer is tip link, if a tech saves ya some money buy em a 6 pack. The small green square=personal message. The green dot is a link to my web page on appliance repair and other general BS I love to post. The letter sends me email.
I love fan letters! LOL

Offline Icehouse

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Re: How do you check a compressor to see if it is good?
« Reply #8 on: May 27, 2009, 03:56:36 PM »

COMPRESSOR TEST CORD
I just use a steel (not plastic) 4 inch square electrical box (1900)  and a  cover with a fuse  for mine, with a grounded 14-3 supply cord going in and a length of 14-4 SJ cord coming out with an alligator clip crimped onto each of the wires (white, black, red, and green). And plastic boots on the clips. Also a short piece of 14/2 SJ cord with alligator clips and plastic boots.
I cut holes in the blank cover to accommodate a heavy duty (15A) on/off toggle switch and a momentary contact push button switch (15A). The white neutral supply wire gets tied to the white wire of the 14/4 SJ cord. This other end of the wire goes straight through to the compressor common alligator clip. The incoming green ground wire attaches to the green wire of the 14/4 SJ cord outgoing line. Using an  alligator clip to attach to the frame of the refrigerator.
The 'hot', black side of the supply, feeds first  through the fuse, then to one side of the  on/off toggle switch. The other side of the toggle switch is wired with the black wire from the 14/4 SJ cord and then straight to the 'run' winding alligator clip. From the output side of the toggle switch, a wire 'tail' also feeds the input side of the momentary contact switch.
The output of the momentary contact switch goes to one side of the 14/2 SJ cord the other wire of the 14/2 SJ cord will go to the red wire of the 14/4 SJ cord. The other end of the red wire will go to the compressor start winding alligator clip. The ends of the 14/2 SJ cord with the alligator clips can be clipped together or connected to a start capacitor.
To use, after verifying which compressor terminals are “common”', “run”, and “start”, just remove the relay and overload, and connect the alligator clips directly to the compressor. Plug the test cord into a grounded receptacle.
Turn the on/off switch on (you should hear the run winding's low hum), and hit the momentary switch to briefly energize the start winding just like the start relay does when it's working correctly.
If it starts and runs with a test cord, it usually means the compressor's OK. You'll want to test the windings with an ohmmeter, though, to be certain there are no winding shorts causing it to 'short-cycle' and run hot.
One of these cords can be handy for test-running other equipment, too. I often just loop the 'start' alligator clip back out of the way, clipping it to the cord, and use this to quickly attach to small motors, etc, to check them.
 


NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

Offline JWWebster

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Re: How do you check a compressor to see if it is good?
« Reply #9 on: May 27, 2009, 10:12:54 PM »
I have mine on a surge supressor/ cheap ass dollar store electrical strip. I hit the toggle and if the compressor is wank the pop up reset button keeps me from screwing in another fuse. dangit.them thangs done went to $4 for 2 of them at CVS. I have a shitload of them. somewhere.:D
May the hinges of our friendship
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About the icons: The beer is tip link, if a tech saves ya some money buy em a 6 pack. The small green square=personal message. The green dot is a link to my web page on appliance repair and other general BS I love to post. The letter sends me email.
I love fan letters! LOL

Offline BrntToast

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Re: How do you check a compressor to see if it is good?
« Reply #10 on: May 29, 2009, 01:36:18 AM »
i have a pro41 relay on a cord, you dont have to mess around with seperate wires or switches

it has the standard pin configuration for most compressors used nowadays

still hav to pull out the ole test cord w/clips for the old GE square box relays from time to time cause those suckers are still around and running

Mayday Appliance Service
Winnipeg Manitoba Canada


The only stupid question is the one not asked

Offline shieldcracker

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Re: How do you check a compressor to see if it is good?
« Reply #11 on: May 30, 2009, 08:39:09 PM »
I believe the question was about testing compressors and not test cords. Now to test a compressor fully you should not only take in to account the electric motor but its mechanical components as well.

Starting with the electric troubleshooting.
A compressor ( and I mean the motor) can fail and have either open windings  or shorted windings, note that the windings can be shorted among themselves or to ground, chassis or the case (it is all the same thing).
Open winding means the compressor wont run and probably trip the overload protection, a shorted winding will either activate the overload or blow a fuse (depending how solid is the short)
Now an open winding is always conclusive test but to distinctively  conclude that a winding is not shorted is difficult because motor windings have a very low resistance. You will require a good deal of judgment (experience) and a very precise instrument to test compressors in this fashion. One exception to above is a winding shorted to ground, this is always conclusive when it shows up, however even these failure modes are not detectable all the times and for this reason many professionals use insulation testers to uncover them. At this point it is a good idea to use a test cord and see if the compressor operates. Note that with use and age compressors can require more starting torque to turn and may require a starting capacitor or hard start to get it rolling.

If your compressor still refuses to run the problem is in the overload or mechanical in nature, if you believe the problem to be mechanical let us know.

Offline Icehouse

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Re: How do you check a compressor to see if it is good?
« Reply #12 on: May 31, 2009, 09:14:51 AM »
I believe the question was about testing compressors and not test cords. Now to test a compressor fully you should not only take in to account the electric motor but its mechanical components as well.

Starting with the electric troubleshooting.
A compressor ( and I mean the motor) can fail and have either open windings  or shorted windings, note that the windings can be shorted among themselves or to ground, chassis or the case (it is all the same thing).
Open winding means the compressor wont run and probably trip the overload protection, a shorted winding will either activate the overload or blow a fuse (depending how solid is the short)
Now an open winding is always conclusive test but to distinctively  conclude that a winding is not shorted is difficult because motor windings have a very low resistance. You will require a good deal of judgment (experience) and a very precise instrument to test compressors in this fashion. One exception to above is a winding shorted to ground, this is always conclusive when it shows up, however even these failure modes are not detectable all the times and for this reason many professionals use insulation testers to uncover them. At this point it is a good idea to use a test cord and see if the compressor operates. Note that with use and age compressors can require more starting torque to turn and may require a starting capacitor or hard start to get it rolling.

If your compressor still refuses to run the problem is in the overload or mechanical in nature, if you believe the problem to be mechanical let us know.


Now after five hours of reading over Copeland Application Engineering Manuals as well as their and Tecumseh Service Data Guide this is what I have come up with, again let me state the information below is from them not I.

FIRST:
Single phase compressor motors have a "Start Winding" and a "Run Winding" with a "Common" connection between them. Therefore the total resistance is the sum of both windings.

SECOND:
Shorted motor windings:occur when the insulation on the windings become defective and allows a shorted condition (two wires to touch), allowing a bypass of the winding. Depending on how bad of a short it is possible for the compressor to operate, but will draw excessive amps.
There should be no reading from any terminal to the compressor motor case using an ohmmeter.

THIRD:
Grounded motor windings occur when the insulation on the winding is broken down and becomes shorted to the compressor motor case.
This can be verified with an ohmmeter by touching one lead to any terminal to the compressor motor case (it is recommended to scrape away paint).

FOURTH:
A compressor motor may have a weakened winding that will short to ground when called to run. It is therefore recommended that a "Hi-Pot" tester be used in conjunction with an ohmmeter to check for insulation failure.
NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

 

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