Mitsi elec split Intermittently tripping mcb

[Anz]

Had a job to look at this unit tripping every now and again.

Another lad has been to this and couldn't figure out what was causing the problem.
I know it's had a new mcb fitted as it's popped quite a bit,
Apparently the system will run for days sometimes weeks then it trips, when I got it to run I noticed the comp was pulling double the amps as per Mitsi info, the comp has been replaced and fresh 410 put in, it's ran for maybe a month and now got a call back as it's tripped again!

I looked at the cond fan too this was pulling not even 1 amp
Mitsi said they have no info on current for fan...

It ran fine on cooling and heating while I was there, the only thing I did notice was on cooling the fan on cond seemed to run for a few seconds knock off then after a few mins do the same, on heating the fan runs normally.

Any ideas?

Cheers lads

[install monkey]

if its inverter then it should be on a motor rated circuit breaker, not rcd protected-preferably- sparks love rcds on outdoor kit but when the compressor stops it discharges down the neutral,hence issues, when u clipped the running current- was this on the compressor leads? if so and if its inverter then you cannot get an accurate reading depending on the frequency- test it at the condenser power in terminals or outdoor isolator, check for nicks in the supply cable and water ingress in the isolator, if its power inverter then you can get running current,actual frequency off the remote controller

normally cond fan circuit is protected via 20mm glass fuses on the pcb

[leegally1983]

prob water in the isolator

[Anz]

No outdoor isolator it's indoor fed. The twin n earth interconnection is just wired straight in to the outdoor. No signs of water ingress anywhere, Mitsi seem to think a faulty relay on the inverter pcb

[Neddy]

You don't need a motor rated MCB on an inverter system as motor rated MCBs are designed for high starting currents. Inverters have low starting current.

When you say twin and earth do you mean 2 core and earth or 3 core and earth?
How much of the twin and earth is exposed outside as twin and earth is not designed to be exposed outside. Check it over.
What type of indoor unit have you? Has it got a pump fitted?

[install monkey]

whats model number, have you meggered the pot?

[Anz]

Can't remember off hand but it's the flat grey cable I call it twin n earth, I know it's not it rang alarm bells when I saw it, I'd say about 6 metres it's ran under a few other sets of pipe can't really see where it goes. It's a 600x600 cassette, no pump it's on gravity, I've filled up the tray and got it to pump to check if that was the problem.

It's an Suz-A12 vr
I have yes, that was ok, but I changed it due to the high running amps

[Neddy]

I would carry out an insulation resistance test on the power supply cable and the inconnecting cable. Has it got a spur inside? If so also check that out and carry out an insulation resistance test on it. Also make sure nothing else is on the electrical circuit, lights etc. If the cables are ok it looks like your down to changing parts. Does the MCB trip when it rains or at any particular time etc ? If you have another outdoor with the same Model no. you swap them and see if the fault follows.

[install monkey]

your system is wired- power to outdoor and power to indoor and a 12v 2 core signal- interconnect, probably a weak circuit breaker, theres loads of fuses on the outdoor pcb- btw cond fan rated 0.24amp, no crankcase heater, check there isnt a electric boost heater on the indoor- as they only operate occasionally
click on the lin below for service manual
http://www.mediafire.com/view/madk166ilj6j3pj/SUZ-A09-24VR%20Service%20Manual%20(OC304revA).pdf

[Anz]

There is defo only the 1 cable going to the condenser. That heater u mention that rings a bell on the wiring diagram.

Cheers lads

[NewmanRef]

Have you monitored the voltage at the supply for any period of time? Had problems in the past especially in more rural areas of voltage drops. Less voltage equals higher running current equals mcb trip. Ask the client if they suffer from power cuts or lights dimming etc. Your original compressor may well having been pulling high current due to volt drop...

[Anz]

Update on this unit!

It's still throwing the breaker, it's had both pcbs on cond, and 2 more visits.
Been back 2day after a recall.
We did IR test on the interconnecting cable and physical check on it, all good. Checked indoor switch all ok, IR test on cond fan all ok. Had it running all day and nothing, had a clamp on the live on the cond terminal watching the amps never saw more than 4amp.
We have now unplugged the dew prevention element to see if this is the issue. Mitsi say a needle in a haystack!

I'm fresh out of ideas! Haha

Cheers lads

[marc5180]

Hi, I assume it's an inverter type unit?
If so have you got the compressor up to Max frequency to see how many amps it's pulling then?
Normally if you put them into test mode from the outdoor PCB then you can watch the frequency increase by about 3hz a minute until Max is reached. Do you have an 'A Tool' to connect?

Also silly question but is there anyway that anyone has connected into your indoor spur to run something else? I've had that a few times with intermittent trips

[Anz]

It is an inverter yes, we've had it in test run using the SW dips. U can hear it ramping right up.
What do u mean A tool?
We have checked there's nothing else on the circuit, traced the cable back to the DB (the indoor is only 5/6 meters away from it)

Cheers

[install monkey]

have u tried swapping circuit breaker, if non of the fuses are blowing on the kit, then its power supply or circuit breaker

[Anz]

It had a new mcb just before the pot was changed, so unless it's a dodgy mcb I sort of ruled that out ;)

[install monkey]

the twin & earth or triple & earth interconnect, is it sun damaged?? not uv rated so shoudnt be run outside, try a temporary sy or swa to see if that cures it- out of intrest, where about in the uk is it , no names ,just general. i might of installed it! haha

[Anz]

It's 3 n E it's knockin on for 10 years old, we have meggerd it 2day n it checked out.
I'm from bolton personally the job is in Huddersfield. There's 4 splits in total and they all have the same 3 n E interconnecting

[install monkey]

not my handy work- only did 4 daikin splits in huddersfield at mities office!, no moisture ingress , it can be frustrating as you convince urself youve sorted it then a few days later u get the call- fitted a few of them mitsi units, did 1 in a chippy in st helens- had jam it between the joists as it wasnt surveyed properly and i was getting paid to fit it- job n knock cash, fired it up and the pot was siezed! haha

[Anz]

Haha! Yeah it's a right pain in the arse, see how it pans out anyway

[marc5180]

It is an inverter yes, we've had it in test run using the SW dips. U can hear it ramping right up.
What do u mean A tool?
We have checked there's nothing else on the circuit, traced the cable back to the DB (the indoor is only 5/6 meters away from it)

Cheers
How long was it in test mode for whilst you were with it? It will go up to max frequency in stages, not straight away.
The 'A service tool' can be plugged directly onto the outdoor PCB which monitors sensors but more importantly will tell you compressor frequency as well.

https://www.acwholesalers.com/Mitsubishi-Air-Conditioners/PAC-SK52ST-Control-Service-Tool-for-P-Series-Units/19488.ac

Does it trip on a particular day or time? Or is it random?
Have you had an inverter checker on it?
If it's not the cable or MCB then it has to be something that isn't energized all the time, maybe a 4 way rv or solonoid?

[Anz]

The customer can't say when it trips they just say well I come to turn it on and it doesn't so they go to the DB and see the mcb tripped.
Not put a inverter checker on however the board was swapped only last week.

In test for a good hour, it's only a small system In an open area so it's running it's tits off so to my ear it sounds as if it's reaching max speed.

With regards to the solenoid or 4wv we had it in cool, heat , auto, dry, temp up , temp down, fan speed up n down , louvers moving.
I just can't see how if were getting the unit to do all it's modes/ features whilst were there why it won't trip?!
See I don't know if it's being left on all night either

It's like the davinci code haha

[Neddy]

Has the site got another outdoor with the same model number? If so pump both units down and swap them. It's a bit of a pain. But you will narrow down your search for the fault.

[Anz]

No that's the only 1 of the same type