Fujitsu split blowing tripping main breaker?

[faberge64]

Help!

I was asked to look at a split in a conservatory, AOYS18LDC indoor ASYB18LDC outdoor.
even running in fan only, after one minute the main breaker in the house trips? its powered indoor to outdoor so i disconnected the supply to the outdoor and the fan ran constantly. i disconnected the outdoor wires and reconnected indoor but there was no 240v supply to the isolator. checked back at indoor and no 240v to the terminal supply to outdoor. the live goes onto a power relay on the indoor and comes back off to the outdoor supply terminal. i get 240 going on the relay but not coming off this does not seem right. so i wired the 240v straight through to get power to the outdoor and put into cooling but tripped the breaker again. i disconnected the comporessor and checked the continuity on the windings but all was ballanced and none down to earth (fluke Tester not mega) but the indoor fan ran again without stopping? reconnected the compressor and tripped breaker again.
So! Phew! am i looking at a new board at the indoor and possibly a new compressor or outdoor board?

any help from anyone who may have had a similar problem would be most appreciated.
sorry for the lengthy post.

[Brian_UK]

Have you checked the cables themselves?

Check the other components of the unts as well, crankcase heater? transformer? something is down to earth somewhere.

[nike123]

Measure with good clamp meter (inrush or peak function) what is current when breaker trips. It could be faulty breaker.

http://hr.rsdelivers.com/product/chauvin-arnoux/p01120703a/ukas206624-f3n-current-clamp-meter/4592698.aspx

[sinewave]

Faberge, what do you mean by 'main breaker'?

MCB feeding the individual circuit for the A/C?

30/100ma RCD main switch feeding the whole Distribution board?


A mechanicaly 'stiff' or siezed comp will not usually show up any problems on a straight insulation test so don't assume that it's OK if meggering checks out.

[faberge64]

i didnt have much time left to check all cables but i will when i go back, does sound like something is down to earth. and it is tripping the main breaker for the house, i'm no electrician but that dont sound too good? what i dont understand is that when i arrived the indoor fan would run for one minute in fan only mode and then trip the main breaker. if it was down to earth it would be instant surely?

[sinewave]

You still have not confirmed what you mean by 'Main Breaker'?

Upfront RCD acting as a main switch?

Or MCB/RCBO protecting that one circuit?


If fault is on outdoor units comp or preripherals that are energised at same the time as the comp then it'll run for a minute or so on fan on indoor before the faulty component kicks in (or out) in this case.

:D

[install monkey]

i didnt have much time left to check all cables but i will when i go back, does sound like something is down to earth. and it is tripping the main breaker for the house, i'm no electrician but that dont sound too good? what i dont understand is that when i arrived the indoor fan would run for one minute in fan only mode and then trip the main breaker. if it was down to earth it would be instant surely?

depends on the insulation-if it is under 1 meg ohm then it will trip quickly if theres no rcd on the circuit then it will take longer. try a new circuit breaker,check the outdoor isolator ,disconnect the compressor off the contactor and try it try the crankcase heater as this is powered in fan only mode

[cool_tech]

i had the same problem on a job found Mr Rat had deciced to dine out on the cable from indoor to outdoor units

[Mavricks Choice]

i had the same problem on a job found Mr Rat had deciced to dine out on the cable from indoor to outdoor units

Agree don't discount your incoming supply from mains or interconnects. Any termination in cabling can lead to a possible HR or burnt connection in the future! Seen it many times over.

Cheers
MC

[SeanB]

Agreed on the cabling. Replaced a cable which had cooked on a joint with a complete new run, new expensive 7 core control cable ( Samsung heat pump, needs 5 cores plus PE on that model, even though we never use the thing in heat mode) when it burnt up at an outdoor connection a few years after the indoor unit was moved to improve cooling performance. Then the darn outdoor unit went and cooked a compressor terminal block 3 weeks later, so was replaced with another complete unit, cooling only, and I will change the indoor unit when I take it off for cleaning. This unit would only trip after running for most of the day, with the trip only occurring every 3-4 days.

[faberge64]

thanks for all the help and advice guys, plenty for me to check out when i go back.