Strange compressor problem

[Spoc]

Now then. Help.
I've landed a strange fault on a four compressor pack.
Compressor one keeps tripping overload intermitantly. it only does it once in 24Hrs and varies in time between 13.00 and 16.00.
I've done the usual and checked Amps, gas, oil, wiring, connections, changed contactors, stripped compressor to check for piston and valve wear, torn my hair out, gone for a brew, slept on it, checked it again, gone for a piss and watched it for two days wihout a fault - to find it tripped again one hour after I left!
It is random to the production process when it trips and doesn't matter if the system is on no load or full load
Semi Hermetic compressor (wired part wound) on R404a controlling several ref and A/C

[taz24]

Now then. Help.
I've landed a strange fault on a four compressor pack.
Compressor one keeps tripping overload intermitantly. it only does it once in 24Hrs and varies in time between 13.00 and 16.00.
I've done the usual and checked Amps, gas, oil, wiring, connections, changed contactors, stripped compressor to check for piston and valve wear, torn my hair out, gone for a brew, slept on it, checked it again, gone for a piss and watched it for two days wihout a fault - to find it tripped again one hour after I left!
It is random to the production process when it trips and doesn't matter if the system is on no load or full load
Semi Hermetic compressor (wired part wound) on R404a controlling several ref and A/C

You have changed the contactors but have you changed the overloads?
Does the compressor have a oil pump on and an oil differencial pressure switch? If it does I would check the oil switch or replace it.
If you have a oil diff switch fitted I'll explain why you might need to replace it.

Cheers taz.

[Spoc]

Sorry. yes i've changed overloads as well. and it does have oil pump and pressure switch. I susspected oil fail as one poss cause I couldn't find anything eles
and swapped controls with another one to try it

[taz24]

Sorry. yes i've changed overloads as well. and it does have oil pump and pressure switch. I susspected oil fail as one poss cause I couldn't find anything eles
and swapped controls with another one to try it

On a Few occaisions in the past I have had faults with oil switches that cause the contactor to chatter.
A slight blip in the contacts for a fraction of a second.
The results of this, are tripped compressors on overloads or as I have seen on one or two occaisions complete compressor failure due to burn out.

If you have checked every thing and if you are at a loss then change the oil diff switch.
It may not be the cause but for what they cost then a new one may be the answer.

Cheers taz.

[sunilbhat]

I think you have checked everything. I suspect there may be voltage fluctuation or phase missing problem instantaneously. Observe current and voltage carefully to srike out possibility.

Sunil Bhat

[Spoc]

Cheers chaps.
best poss answer is chattering contactor or power surge but it has a BMS controller which locks-out in the event of a fail and a four min time delay to stop restart (or it does when I watch it) If I 'make' a fault the BMS shows an alarm status and does a print-out. The head-scratcher is if it was a power problem then why only that compressor trips and no other? If it's a control problem then why does swapping the controls over with another compressor not move the fault?

[Spoc]

Oil diff sw is also electronic not mech bellows type

[taz24]

Oil diff sw is also electronic not mech bellows type

You're buggered then.

taz.

[Spoc]

Errr......Thanks......


Glad I wasn't been too thick and missing the bloody obvious though.

But many thanks for trying. If anyone eles has any ideas please list them

[taz24]

Errr......Thanks......

It looks to me like you have done as much as you can.
Sometimes we have to admit defeat and admit we do not know.
You have explained all the possible faults and outcomes. Your fault finding has been explained well

Sometimes you just have to let the thing run and time will reveal the fault.

I think you are doining the right thing and eventualy the fault will reveal its self.

Cheers taz.

Ps the buggered bit was my attempt at humour.

taz.

[monkey spanners]

Has it got a thermistor module (INT69) i've seen problems with these.
You can get a thing called a 'tatle tale' from dean and wood that you wire across a control switch and if it trips the indicator changes colour to show which one is causing problems. We used one to prove that someone was turning the power off overnigt to cause meat to spoil in a coldroom.

Jon

[Plank!]

I think you have checked everything. I suspect there may be voltage fluctuation or phase missing problem instantaneously. Observe current and voltage carefully to srike out possibility.

Sunil Bhat

If you suspect a phase problem stick a phase failure protection relay in the panel, something like the telemecanique RM4TR32 would do the job. This nodel has a selectable 10sec delay, so can be used to ignore transient spikes and only trip when the supply faults for long enough to cause a problem.

We had a problem with some grasso duo screw packs, they kept burning out, and often welding contactors. Everything checked out ok, contactor size was more than enough, yet we still had a big pile of dead contactors. By chance i overheard someone on site mention that the lights had dimmed, PC's crashed and control fuses blown in the loading bay door systems, on the same day the last contactor failed.

I Fitted phase protection relays, and before i'd even finished the second panel, the first tripped on a serious overvoltage. Eventually the electricity supplier admitted there were "fluctuations" and the problem went away

regards
Steve

[C Bagtas]

Hi,
try to Megger the motor winding it might be slight problem in insulation.
Cesar

[Pooh]

Spoc
you have a part wind compressor I beleive have you changed the timer if fitted, I have had this were the timer has not brought the second windings in and the primary winding overloads have tripped. May be worth looking at, I have had the same problem with star delta comps as well, changed hundreds of pounds worth of bits for the sake of a thirty pound timer.

Ian

[Spoc]

The first tool out is always the test meter. One to test to prove live or dead. Then Insulation. Then current.
It should be noted that this system has also had the overload set higher than all the others since we took the contract over.
That might be possible about the part wound time delay. It's only a second.....
I'll just get my coat.....
I'll be back in a couple of hours love....

[bill1983]

intermittent problems are always a pain. i imagine we've all had similar experiences. my boss always advocates changing cheap parts first then working your way up the price scale. the tattle tale device sounds like fun i would get a few and fit them across all switching devices. before i did that i would check the compressor loads at various parts of the day to see if that can give you an indication, eg high suction superheat caused by reduced load could cause thermistor trips, low could cause oil foaming if liquid is getting into the crankcase. the compressor will always trip on a safety switch if it operates outside that switches parameters. by the same token if one of those switches is faulty your only hope is to get lucky or replace them each time the comp trips. is the compressor the lead compressor 24/7 or do the run hours try to equalise via the pack controller?