Rebuild semi hermetic compessor not starting

I have a problem with Frascold B 2 10 Y semi hermetic compressor R404a, I was called out on a cold room freezer the start and run capacitors had blown, I checked the compressor and found (as suspected) it was faulty,
I ordered a rebuilt compressor with new electrics, fitted comp and electrics with the connections as recommended by the supplier, (I replaced gas and filter drier and vacuumed ) started filling system with 404a started the comp topped up the refrigerant to the correct level, All OK, ran the system for about 15 min and switched the system off to replace covers etc switched on the compressor just buzzed, checked electrics OK still buzzed, shut off service valves disconnected pipework comp cooled down ran with out the pipework ran OK, Checked caps, elect connections, wiring, blockage in system, still no good phoned suppliers they set another rebuilt comp, still the same,
Run cap 24uf term 4&2 on relay
Start Cap 200 - 250uf term 1&4 on relay,
Live on 4 on relay,
Neutral on 5 on relay,
Comp terms -
Start V to 2 on relay,
Run W to 4 on relay,
Common U to 5 on relay.
I am at a loss no what to do next. Any ideas. 2 faulty compressors ?

have u checked the gauze on the tev orifice,replace the orifice,did u do an acid test on the old oil? may req a suction burnout drier and an acid neutralizer,whats the running current how does it compare with the nameplate?

Its a synthetic oil, On standing the head pressure is about 10bar on stop does not move even when starting,
the compressor goes straight to buzzing, it strikes me that the start cap is not coming in, I've tried replacing the new relay.

Thanks for your help. I will check the TEV but I don't think its blocked there seems to be a quick response
on the return or back pressure plus it did run for 15min.

Check the circuit supplying the freezer for volt drop

Found this,

http://www.frascold.it/pdf/INSTRUCTIONS/M041-08.pdf

I'd be concentrating on the start electrics and their wirning first, the fact it ran to start with before the system was fully charged (when the load on the comp would be lower) makes me wonder if they are connected correctly or faulty.

Basically common gets a neutral, run a live, start is permanently connected to the run capacitor and the relay switches the start cap out of circuit with the start winding once the relay senses the high voltage thats present in a running motor on the start winding (acts a bit like a transformer) once its up to speed.

To test things are doing what they should be, measure the current in the start cap wire when trying to start, no current means its not in circuit, same with the run cap. Current in the start cap wire once running means the relay isn't switching the start cap out of circuit.

You can test a comp manually so long as you wire a suitable switch inplace of the relay and switch it yourself.

Some relays need to be mounted the correct way up to work.

Have you confirmed the volatge to the compressor when its trying to start?

Have you checked the capacitors values?

Jon :)

Quote:

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Originally Posted by monkey spanners

Found this,

http://www.frascold.it/pdf/INSTRUCTIONS/M041-08.pdf

I'd be concentrating on the start electrics and their wirning first, the fact it ran to start with before the system was fully charged (when the load on the comp would be lower) makes me wonder if they are connected correctly or faulty.

Basically common gets a neutral, run a live, start is permanently connected to the run capacitor and the relay switches the start cap out of circuit with the start winding once the relay senses the high voltage thats present in a running motor on the start winding (acts a bit like a transformer) once its up to speed.

To test things are doing what they should be, measure the current in the start cap wire when trying to start, no current means its not in circuit, same with the run cap. Current in the start cap wire once running means the relay isn't switching the start cap out of circuit.

You can test a comp manually so long as you wire a suitable switch inplace of the relay and switch it yourself.

Some relays need to be mounted the correct way up to work.

Have you confirmed the volatge to the compressor when its trying to start?

Have you checked the capacitors values?

Jon :)

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Very good that monkey I am to lazy to type that lot

Ive tried a direct circuit from the compressor contactor excluding all other circuits such as evap fan, defrost timer, cond fan, solenoid valve Kept open with a magnet (I fitted new aprox 6 month ago), The wiring is a mess but checks out ok I don't know who did it. I seem to keep coming back to the caps, there dosent seem to be enough umphh to start the comp,

Thanks Boys, We are a sorry lot, I should be having a pint and watching my boy 17y playing for Newton Abbot 3rds (cricket)

any other ideas

Sorry 3rds (cricket) I forgot the shift

By the way it's a single phase comp, and I test routed it direct from the fuse board through the contactor to the comp.

Thanks I have already checked the instructions http://www.frascold.it/pdf/INSTRUCTIONS/M041-08.pdf
Going back to the burnout and blockages idea, I once came across a second hand compressor that I fitted (requested by customer) when I started the sys the refrigerant turned black and blocked the filters, since then I had a mate who was in to compressors & hydraulics make up a clear reclaim tube so I am able to visually to detect heavy contaminant (usually Black) , I know that this is not 100% but it gives me a good idea of the condition of the refrigerant in the system and damage to the comp

Well I tried all sorts, percussive maintenance, dynamite, friendly persuasion, the dammed things still wouldn't work, so in the end I fitted a 2.5hp hermetic compressor, works fine now. Probably 2 duff compressors.

Thanks for your help.

Mike

This sounds like a Commerical equipment issue and not Industrial. Might get more resposnes in the forum.