Testing A Compressor.

[G_Young]

Hi, i've looked through the site for a good example of how to test if a compressor is down to earth...
i cant seem to find a straight forward answer of how you do it exactly and the sort of results you would expect if it is down to earth or okay. any assistance? thanks.

[acgibo]

its simple G, put your tester to continuity one probe on earth and one probe on a phase, if you get continuity its down to earth.
you must test all phases (lives)
good luck mate

Gibo

[frank]

Hi, i've looked through the site for a good example of how to test if a compressor is down to earth...
i cant seem to find a straight forward answer of how you do it exactly and the sort of results you would expect if it is down to earth or okay. any assistance? thanks.

If a winding is leaking down to earth then the winding Insulation is breaking down. To effectively test for this you need an Insulation Tester.

An Insulation Tester delivers a low amperage current at 500v into the winding with the return path through earth. If you get a reading of 500,000 ohms or above then the winding is deemed to be acceptable although, I and most others, would reject a reading below 1m ohms.

Using an Ohm meter to check for insulation breakdown is not normally useful due to the low voltage at the probes, unless the insulation has completely broken down and then you measure a short circuit.

[US Iceman]

And, if you are doing a megger test make sure the compressor is not in a vacuum. The motor insulation resistance is lower in a vacuum and you could blow the insulation when the megger test is done.:o

[jamcool]

Also remember its each leg of your comp. to earth a test across legs will give you a wrong reading.

[G_Young]

thanks for all your help!
going back to what frank said with the insulation tester/meggar... you have start, run and common on the compressor i think?
do you test between earth and each connection on this. i.e earth to start, earth to run etc?

[Brian_UK]

thanks for all your help!
going back to what frank said with the insulation tester/meggar... you have start, run and common on the compressor i think?
do you test between earth and each connection on this. i.e earth to start, earth to run etc?In theory, assuming that the windings are intact then it won't make a great deal of difference, but.....

How much time you you going to save by NOT testing each terminal?

It is safer to test each in turn then you know that you have done a full and complete test.

[monkey spanners]

Make sure the power is off first, tape any mcb's off as someone may turn them back on while your working.
Right first thing you need is a note book. Draw a picture of what colour wires go where. If they are the same colour put some tape on them. Remove the wires from the compressor terminals, if you leave them on you could be testing a fault on the incoming cable.
Attach the black probe on you insulation tester to a good earth, touch the red probe to another good earth and press the test button, you should get a dead short if not recheck your earths.
Touch the red to a compressor terminal and press the test button, if its burnt out it usually shows as a dead short, if its below 1m ohm it could be damp on the compressor terminals, or possibly a sign of acidic compressor oil. Test all the terminals in turn and then recheck with a good earth again (no good testing if the black probes lost its conection)
I would expect a new or good compressor to be over 10m ohm, over 1m ohm will run but i wouldn't be happy with it, below may set of RCD trips.
If all checks out ok test between the windings to find their resistances e.g. if thee phase test L1 - L2 L1 - L3 & L2 - L3 you sould get near enough the same reading between each. If not you may have one or two duff windings. The resistance will change slightly with the temperature of the windings. If it has a external klixon it would be worth removing it and testing between L1,L2&L3 and the klixon terminals as this is the star point of the windings.
If single phase test between the start terminal - common terminal, common terminal - run terminal & start terminal - run terminal. The resistace between start and common and the resistance between common and run should add up to the resistance between start and run.
Don't insulatince test any thermistor connectors as the are low voltage.
Oh and let go the test button BEFORE removing the test lead or you will charge up the winds like a capacitor and get a nasty shock when reattaching the wires:mad:

Cheers Jon

[bernard]

Hi

The following is the tests I carry out prior to fitting a single phase comp or testing faulty comp.

Ensure that the sysem is completely isolated from mains

Connect one lead to common pin on the compressor,connect the other lead to the earth post,should read infinity or zero,if 0-2meg ohms compressor is down to earh.

To check comp winding resistance set meter to ohms,connect one lead to common and to start,this is the start winding resistance.

Common to Run for run winding resistance.

Start to Run will give complete winding resistance.


Theres nothing worse than fitting a new comp to find its faulty.


Regards Bernard:)

[Pooh]

Be aware that some modern compressors have solid state temperature sensors inside the windings which do not take kindly to the use of a megger (insulation tester)
I cant remember the correct designation of this type of protection but if required I can find out.

Ian

[G_Young]

wow! thanks for all the help. thats exactly what i needed to know... just wondering what a klixon does? i've heard about heater klixons etc, but im not 100% sure what they do?

[Pooh]

The klixon is a current overload device which turns off the comp if there is a problem.

Ian

[G_Young]

oh right. what sort of problems could you expect from a klixon if it is knackered then? not cutting out the compressor, not allowing it to start, cutting it out to easy?

[Pooh]

If a Klixon is knackered the comp will not run however there has to be a problem to cause the klixon to fail in the first place, I have never had one fail on its own.

Ian

[US Iceman]

Be aware that some modern compressors have solid state temperature sensors inside the windings which do not take kindly to the use of a megger (insulation tester)
I cant remember the correct designation of this type of protection but if required I can find out.


I believe those sensors are thermisters. One per phase. The sensors connect to a "black box" which monitors the winding temperatures and opens the control circuit if the windings reach a specific temperature.

[Pooh]

US Iceman the ones you are talking about have seperate connections to the thermistors so should not be damaged if using a megger on the main windings. The ones I am talking about are mainly used in hermetic compressors used with Hydrocarbon refrigerants as they are contactless so cannot cause a spark.

Ian

[Alan B]

Frank
I wouldn't be happy with a measured impedance of 1m Ohm ie 1000 Ohm.
1M Ohm ie 1000000 Ohm is surely what you mean.
Alan B

[G_Young]

If a Klixon is knackered the comp will not run however there has to be a problem to cause the klixon to fail in the first place, I have never had one fail on its own.

Ian

sooo... would something like having the sytem run out of gas weaken the klixon through the compressor?

[Brian_UK]

Yes, the Klixon, if fitted to the outside of the compressor will perform two functions.

1. It will monitor the amperage drawn and trip if it goes too high, motor overload.

2. It will also monitor the case temperature. This can and will rise if there is a refrigerant problem.

Normally the Klixon is a robust item and will only fail through severe mis-use. If it trips then there is normally a good reason.

[frank]

Frank
I wouldn't be happy with a measured impedance of 1m Ohm ie 1000 Ohm.
1M Ohm ie 1000000 Ohm is surely what you mean.
Alan B
Yes Alan. 1 mega Ohm, i.e. 1,000,000 Ohms

[monkey spanners]

My insulation tester (Robin, make not name:D ) has three voltage ranges, 250v, 500v & 1000v pressumabley the 250v range would be ok on the solid state internal starter things, as its no more voltage than they see in normal use?
I think the solid state starters work by increasing their resistance as the voltage passes through them (wired in series with the start winding) like having a dimmer switch on the start winding. I believe that they are also found on some HFC compressors.

Cheers Jon

[bernard]

http://www.thermagroup.com/documents/FieldCompressorGuide_000.pdf

http://www.benshaw.com/literature/applications/RCAN.pdf


http://www.aemc.com/techinfo/techworkbooks/megohmmeters/tech_megohm.pdf



Found this which may be of interest

Regards Bernard:)

[Brian_UK]

Thanks Bernard, useful links.

[Dan]

Be aware that some modern compressors have solid state temperature sensors inside the windings which do not take kindly to the use of a megger (insulation tester)

From Copeland's Application Bulletin:

The solid state sensors and the electronic components
in the solid state module are delicate, and can be damaged
by exposure to high voltage. Under no circumstances
should a high potential test be made at the
sensor terminals with the sensor leads connected to
the solid state module. Even though the power and
pilot circuit leads are not connected, the module can
be damaged.

CAUTION: Use Ohmmeter with a maximum 9
VAC for checking. The sensors are sensitive,
easily damaged, and no attempt should be made
to check continuity through them with other than an ohmmeter. Any external voltage or current
applied to the sensors may cause damage requiring
compressor replacement.

[taz24]

sooo... would something like having the sytem run out of gas weaken the klixon through the compressor?

Low gas and no suction cooling would cause this yes.
I have worked on compresors that have got too hot due to condensing problems and the comp has short cycled on the klixon causing the klixon to burn out and be constantly open circuit. If the klixon fails it genraly is for a reason.
Some hermetic comps have the klixon on the winding inside the comp housing.

Cheers taz.

[Larry2]

If a Klixon is knackered the comp will not run however there has to be a problem to cause the klixon to fail in the first place, I have never had one fail on its own.

Ian

I had a klixon in a scroll compressor head cause system shut-down. It was inserted into a "well" in the scroll compressor head and insulated with a thin layer of kapton. The insulating Kapton layer failed. That shorted the 24 VAC control circuitry to ground. That blew the fuse in the control transformer, rendering the system non-functional.

I recently replaced that klixon along with it's insulating wrap. The kapton insulating layer was demolished and it came out in bits. I have no doubt that the klixon itself is in good shape. It has a rather high setpoint, 270F or so.

These klixon switches are a last line of defense against fault. Or a first line of defense in budget units like mine.

Mine was probably a latent failure from a direct lightning strike to the home electrical system. It took years before the damage was enough to blow the control circuit fuse.

[NoNickName]

MY 0.02. I would not accept any insulation test below 15 MOhms. That is our standard procedure.
A 7Mohms should pass in most companies, but that relatively low resistance may be due to broken isolators (threaded studs isolators where the power cables are fixed. If too much torque is applied when installing the cables, the laquered isolators crack).