Fujitsu Internal Fuses?

[sinewave]

Hi Guys,

I have a Client that's reported 2 independent 7 & 8kw Cooling only Cassettes that are totaly dead on the wall mounted controllers.

I've asked them to get their Sparx to check the supplies to both units and he's reported back alls fine up to the wall mounted isolators.

Therefore I'm assuming that it's too coincidental for two units both to fail completely (including power to the the controller) and that theres been some sort of voltage surge that's popped the internal fuses.


Does anyone know off hand what size they would be and if this is a likely diagnosis?


It's a long drive to site so I want to be prepared if all it needs is fuses.

Looking at a small 2.6kW unit we have in our office the fuse looks like a standard quickblow RS type glass 30mm fuse?

[aza]

Have the sparks check the cassettes above the ceiling for isolators, if electricians have been in their testing they may have left a isolator switched off.

I have travelled many miles just to throw a switch more than once.

[sinewave]

Hi Aza,


No there's nothing been done there and there's no isolators in the ceiling, there fed directly from the outdoor condensors in 4 core SY

[Andy AC]

Sinewave I am pretty sure they are 3.5a time delay 20mm. There may also be a 5 amp fuse in the top of the condenser.
I had this a couple of weeks ago - got a call saying two fujitsu wall mounts not working but power to them, put new fuses in them and BANG, bye bye pcb.
It turns out the maintenance electricians who tested to see if there was power, were doing a phase change or something else major over the previous weekend and caused a massive power surge.
Because of what had happened we checked all the other units in the building. In total we had to replace the boards on 6 out of 9 fujitsu wall mounts.
Strangely though, it was only the air conditioners that suffered, all over equipment seemed to be ok.

Andy

[monkey spanners]

Had this the other week, Dave says its 20mm 3.5A on the indoor uint and 5.5A possibly 5A on the outdoor board. This was caused by a dodgy cch.

Jon

[sinewave]

Sounds ominous Andy


The one inside our 2.6kW wall mounted Inverter is a 30mm 20A fuse so I'm assuming that the one in a 7 & 8kw Cassette is bigger?

[Andy AC]

Sounds ominous Andy


The one inside our 2.6kW wall mounted Inverter is a 30mm 20A fuse so I'm assuming that the one in a 7 & 8kw Cassette is bigger?

It's only the controls, indoor electrics/fan being protected, not the compressor as that would be covered by the mcb at the mains board so a 3.5 fuse would normally be ample.

On your wall mount, you may have another fuse that protects the electonics, as it sounds like the 20A one is for running the condensing unit as well. I am assuming your wall mount is power to indoor?

Andy

[Danny11]

Have you belled out the wiring.Iv had it before where mice/rats have chewed through SY cable."strong little s**ts"
Also check that the dip switches on the controller are right.

[sinewave]

Had a look-see today and it looks like there's been a volatge surge on site on one of the phases.


One 8kW unit had 115 volts on all three of the remote control wires to earth!


The other 7kW unit had 2.4 volts on it's remote control wires to earth.


All internal fuses OK and both smoothing boards OK


Reckon both main PCB's are fecked and at least one wall mounted hard wired controller!

[paul_h]

Had a look-see today and it looks like there's been a volatge surge on site on one of the phases.


One 8kW unit had 115 volts on all three of the remote control wires to earth!


The other 7kW unit had 2.4 volts on it's remote control wires to earth.


All internal fuses OK and both smoothing boards OK


Reckon both main PCB's are fecked and at least one wall mounted hard wired controller!

that's some very fried systems.
edit: but in general reply to some of the responses here:
Air cons don't like power surges, their MOVs blown pretty easily, that shorts the circuit to blow the fuse, you can make a decent income repairing them where other choose to quote for entire now PCBs at $300 odd each.
The fuse is usually a 20mm long 3.15a fuse, the MOV is a 471V rated varistor.
I have lost count the amount of times a power surge in a neighborhood has taken out all the air cons but nothing else. It's no just fujitsu though, a/cs in general seem to blow without anything else being damaged.
Anyway, right next to the fuse there's a circular round thing (MOV or metal oxide varistor). Look to see if that's blown. If it is, a power surge caused the damage.
Option 1: just grab your pliers and rip it out making sure the two wires that went into it dont short. Replace the fuse and switch the aircon on, if it works, no damage done, the MOV did it's job and protected the circuits from the power surge, replace the MOV if you want to*
Option 2: Stock up at the electronics store with 471V 12mm diameter varistors for $1.30 each, carefully desolder the blown varistor with your soldering iron and solder sucker, test a/c with new fuse, if it works, solder in replacement MOV

* what? you were going to throw that PCB away after theat $1 part did it's job and protected the chips anyway, at least ripping of the blown MOV gave it a second life before anybody just chucked it away.
The MOV is designed to short, to cause the fuse to blow in order to protect the chips from the surge. It makes no sense to toss the PCB just because of a protection device activated.
Become the smart guy on the street, rip off the MOV, replace the fuse and give the PCB a second chance of life before throwing it away (the chips will fry the next time). Or buy some replacement MOVs for $1.30 each and keep the PCBs going forever.

[paul_h]

Sounds ominous Andy


The one inside our 2.6kW wall mounted Inverter is a 30mm 20A fuse so I'm assuming that the one in a 7 & 8kw Cassette is bigger?

Indoor units seem to universally have a 3.15A fuse, it's mainly for the indoor fan motor and the circuit boards themselves. Outdoor units have a 10-30 amp fuse as a main fuse (for the compressor) - depending on unit size), plus a 3.15-6A fuse for the control (PCB, R/V, CFM, CCH etc again depending on unit size small units 3.15A large 6HP ducted - 6A)
You'll find in a power surge, the control system fuses blow first (mainly in the indoor from experience too). They're the lowest rated fuses at 3.15A and closest to the mains supply, and right next to the MOV.

[sinewave]

As stated ALL fuses were OK.


So would the MOV blowing allow 115V to be present on the 3 remote control wires?

[paul_h]

As stated ALL fuses were OK.


So would the MOV blowing allow 115V to be present on the 3 remote control wires?

Nah, sorry if I didn't make much sense. But I said your systems look very fried, that info about the fuses and MOVs was a general comment on some other posts in the thread.
Your fuses are OK, that means the MOVs didn't blow. a MOV blowing shorts the circuit and blows the fuse.
The MOVs on your boards failed to blow so the circuits got fried, it's time for the bin for them.

[Andy AC]

MOV's
I'm gonna give that a try paul, thats well worth knowing. I still have most of the boards I replaced so I'll give it a try next time it happens. I can see this sort of thing happening again on that particular site.

Andy

[sinewave]

Good ruse that!


Fit a new board at £150+ then fix the 'fried' board for a £1.50 then keep in stores until you can re-sell it for £150!

[nike123]

Nah, sorry if I didn't make much sense. But I said your systems look very fried, that info about the fuses and MOVs was a general comment on some other posts in the thread.
Your fuses are OK, that means the MOVs didn't blow. a MOV blowing shorts the circuit and blows the fuse.
The MOVs on your boards failed to blow so the circuits got fried, it's time for the bin for them.

Not necessarily. I fixed almost all Fujitsu PCB-s who's MOV didn't blow because, generally speaking, fried circuit is power part of PCB which is galvanicaly (by transformer) separated from control part of PCB, and simple change of Graetz bridge or rewinding the transformer or something similar, solves the problem. You need to have some knowledge about troubleshooting and servicing electronic circuits or you could take it to the local TV repair shop.

[bennny01]

Hi ! do you know where I can by the MOV, my one is blow and I can not read value of this component. Fujitsu don't sell them.
Thank.

[paul_h]

RS spares, jaycar, DSE, farnell, any of the electronics shops. I've bought a bunch from all them at one stage.
Get 470V 12mm diameter varistors. edit: and probably a 5mm 3.15A quickblow fuse