cold store problem

[Trevor R]

Hi would appreciate an some opinions .. A friend of mine owns a cold store \ refrigerated transport company, and has asked if I could help him with a problem - the cold store has three compressors \ cooling units units 1 & 2 will run all and every day long without an issue - unit 3 will run for a while and then cut out - the panel indicated overheating.

A number of people have looked at it with different solutions being offered - the first is "you'r running close to the limit of the supply into the building" - first question is - if it was running close to or above the authorised supply capacity I cannot see how that would affect just the one compressor - (I'm domestic and liken this to the supply fuse blowing if the capacity was exceeded - thus everything stopping). He has been told - and I have seen it in writing that the site has a 100A supply ... I do not know what it is but it is 415v 3 phase - so I very much doubt the 100A statement - the supplier when told has offered to upgrade the supply for the token sum of £60 grand!

My friend turned off unit 1 and ran unit 2 and 3 - unit 3 then cut out again showing overheating - then ran unit 1 and 3 with unit 2 off - and still unit 3 cut out with overheating showing. So the next solution offered was "You need a panel builder to check the panel"

And the third solution offered was you need to check the connections are tight - with the 4th person filling out his engineers report which reads "On inspection found compressor contactor failed due to ?" Because of the different comments from alleged experts my friend asked me to look - I did explain to him that I am domestic and have no experience with cold stores ... but being a mate felt that I would like to help.

 

[Moses]

Check the Compressor contactor.
If the compressor is loosing one phase while running then the windings will overheat.
Try renewing the contactor.
Failing that the contactor windings will need to be tested.

 

[Richard Burns]

I might also be looking for physical rather than electrical problems (though it could be electrical).
Is the compressors vents clear, is the head breaking down and causing resistance to the motor.
It could be worth clamping the supply to see what it is taking in case the motor is being obstructed.

Limit of supply is rubbish, correct and tight connections is worth checking but at that rate you would see the melting cables!

 

[bugsy]

Has anybody checked the compressor?

 

[Edd]

this sounds like an over heat on the compresser, look at the posts above.. if the others are running fine and no supply is dropping out then its a compresser problem

 

[oldtimer]

These systems are useally sized for 120-150% of capacity so yep 2 compressors will run with maybe the 3rd cycling in and out but this depends on the control system if the comp cycles too much then it will trip out or it may just have a fault. Also check if you can change the lead lag configeration or is this 3 seperate systems feeding into 1 cold room?

 

[JD6400]

You need to check the current and voltage draw on the third unit with a clamp meter or such like .
Then look on the motor face plate ( make sure you tally up the data on the plate as there will probably be a couple to go from and are listed in the same order in each box) this will most likely be the lowest set of numbers as it will be 415v 3ph you need to look for .
Then check the overload settings on the the contactor and make sure some numpty has not altered them .

If the motor is drawing more than the face plate rating and the voltage is fine , it could be one of many things and i would suggest taking a photo and reposting with what you have found up to that point , we could do with knowing if it is a direct drive or has belts and is it s scroll type and its age ?

 

[Knobhead]

Who has your mate had to look at this unit? A reputable engineer would have given a definite answer.

Loss of refrigerant springs to mind, this can only be put right by some one licensed to do the job. There will usually be a gauge on the tank showing pressure, compare it to the others. Heat exchange radiators are another problem area, are they clean?

You don’t say the KW rating of the motors so we’re just guessing as to the supply.
To be honest I don’t see it being an electrical problem.

 

[Engineer54]

Every compressor i've worked on, have thermistor or similar type of over heat protection embedded in the windings. If one of these thermistors is breaking down, or one of the windings is breaking down, then the compressor will trip out on overheat. First a check on the windings is needed, then the thermistor protection circuit. If it is a thermistor problem, they can be bridged out with a compensating module!!

If i was your mate, i would be enquiring with the manufacturer of the compressor, or even getting one of there technicians out to check this unit out. Other than that, it could well be on the gas side of things as Tony has stated....

 

[Knobhead]

Without information on the compressor units once again we’re just guessing.

Please give the cooler make and model number. “Over temp” could relate to umpteen things.

At least give the basic information.

 

[Marvo]

Find out where the overheating alarm sensor is located. It could be sensing motor winding temp but it could also be sensing discharge/condensing temp or oil temp or even off-coil air temp. Until you know exactly where the alarm sensor is you don't know what type of problem you're looking for.

If the sensor is on the motor windings then just do the usual barrage of motor tests, IR, on-load I&V, start I etc. If everything checks okay then test the thermistor or klixon or whatever the sensor is.

 

[micknew]

Best advice would be to employ a qualified electrician who is trained in industrial electrical installation.