View Full Version : Units that have taken a power surge. Please help.

15-02-2007, 01:38 PM
Hi to every one @ Refrigeration Engineer .com, I am a new member to the forum but have known about it for a while and found it to be a great help for me and others.

My question: I, have a customer that has two units (MITSUI) that have taken a power surge after a electrical storm and now do not switch on, my first thought is the, PC Board, of the unit is fried, I, have checked the, Quick Blow Fuse, and it is ok.

The unit is a, Wall Mounted, unit with power to the indoor, there are no circuit boards on the outdoor unit.

Is there anyway that, I, can check the, PC Board, to see if it is, fried, and also could it be anything other than this.

The, PC Board, is also connected to the:
1) Remote Sensor, and, Operation LED's, witch are on a small separate board, could this also need replacing?

2) Im sorry, I'm not sure of the name for this part, I, think it is a, Transformer Coil, if some one could please correct me. I will describe it and, I, have also attached a picture of what it looks like:
It is like a bare coper wire rapped around maybe a magnet in the center, its about, 1 inch square, in size, and is located on the indoor unit behind the electrics box. It maybe a transformer or resister, I'm not sure. Could this also be a problem?

Any help from anyone how may have any experience in this area is much appreciated.

The part I'm not sure about looks like the attached file. This is not the one from the units in question but is very simile.

The Viking
15-02-2007, 07:25 PM
But problems following a power failure or a power surge is normally:
-Overload relays
Pretty much in that order.

15-02-2007, 08:49 PM
is this unit an inverter as the part you describe could possibly be a noise filter

15-02-2007, 09:00 PM
No the units are not inverters.

The part that, I, tried to describe, I, think is a, Transformer Coil and is about, 1 inch square, in size it is located on the indoor unit behind the electrics box. I have no experience with these and don't no how to test them if poss. not sure if a surge would effect it or not.

The part looks like the attached file on the original post @ the top of page.

The Viking
15-02-2007, 11:48 PM
That picture shows a transformer.
You should have continuity if you measure yellow-yellow or black-black. You should not have continuity if you measure yellow-black or any colour-ground.
(sorry can't make out the wiring on the one in the background).

These rarely fails, in fact, they are probably the most reliable part of a modern system.

You should also find that you have mains voltage on the yellow leads and 12-25 volt between the black ones (but I might be wrong here, the colours might be the other way around)

16-02-2007, 11:01 AM
The attached picture is not the one from the units them selves, it is just very simile.

Sorry for the confusion. Off hand, I, can't remember the wire colors but, I, do understand what you are saying and shall test it when, I, go back to the clients house.

If there is any more info from anyone, I'm, much appreciated thank you.

16-02-2007, 12:33 PM
You should trace the entry of the supply line into the indoor unit. There is a possibility that the live supply enters the indoor unit via a very small fuse somewhere inside the indoor unit (before entering the main PC Board).

16-02-2007, 01:20 PM
No, I, get power at the, PC Board, but the unit will not power up. have tried the, PC Board, and that is not the problem now that works, OK,.

The units, I, don't think are expensive but the guy who owns them is a, Old Chap, on his own and, I, so far haven't charged him and wont unless, I, fix them.

The guy who originally fitted them wont help him, and, I, am now wondering if it could have caused any other damage, IE, Fan Motors, Compressor, I, haven't had much experience with, Power Surges, on units other than once which was the, PC Board.

Now, I, know the, PC Board, is not the problem should, I, change the, Remote Sensor and LED Board, and the Transformer? The units are not expensive ones and there is not much to them pretty basic units.

Dont know what to do for the best here.

16-02-2007, 01:27 PM
I was just working on a few units this week that had been subject to a power surge.

Apparently the high voltage line had come off and sent a surge through all the properties which were fed from this supply.

Several streets were affected including a Daikin (Inverter) and a Mitsubishi electric (fixed speed unit) both in a school.

Nearly all the units that I looked at had the same problem.The fuses on the PCB's were blown an the varistors were now faulty so putting in a new fuse resulted in another blown fuse.

Some boards were revived by breaking the varistor off the board and putting in a new fuse.

The Viking
16-02-2007, 09:29 PM
Well if we take one step back.

The unit is single phase, got a direct on line compressor and the mains feed is to the indoor unit?

You should be able to run the outdoor unit by giving it mains voltage, effectively bypassing the indoor unit (NOTE: only as a test, for a short period), if this works you know that the outdoor unit is OK.

Then check the wiring diagram and see if you can do the same with the indoor fan.

Regarding the transformer, see my previous post.

I would say that the sensor and the LED board should be OK, as they are down stream from the main PCB and less sensitive.

If all the above checks out all right, then I would have a second look at the main PCB.

17-02-2007, 11:47 AM
Thanks for info, your all a great help.

I will be going back to the cliants house on, Tue, when, I, shall try all that has been said here and hopefully get to the problem.

If in the mean time any one has other experiences with, Power Surges, please, I'd like to here about them to build my knowledge up in this area.

Many thanks every one.

19-02-2007, 04:09 PM
RCD / surge protection required once fault is sorted me thinks.


19-02-2007, 04:57 PM
Yes, I, think surge protection is a good idea, and also should be standerd on all new property.

20-02-2007, 01:42 PM
I suspect the transformers, cheap ones toast very easily, then the PCB: "economic" units rely on the transformer as a "ballast" and little else for protection, the PCB, if half-faulty might show lights but not activate relays etc etc.

If the A/C was bought from the "MITSUI 599/699 inc installation" company try ___.acdirectairconditioning.com for the spares and "back up". I have not had nor desire dealings with them since they came in as market busters and from what I have seen of the units and service:(...

Mains line over-voltage faults are covered in Spain by an insurance policy from the electricity supply company - provided the fault was locally generalized and reported "immediately". They do re-imburse reasonable repairs and replacements on presentation of legitimate bills and complaint!!!:)

20-02-2007, 11:34 PM
Thanks, Momo, for that info, I , was suppose, to be going to the, client, today but he changed to, Friday. After everything, I, have discovered, the transformer will be the first thing that , I, check.

Mr Cooling Magic, Yes your quite right, I, remember spending hours trying to get to the bottom of newly fitted units in a, restaurant, and them not working, kept tripping out, after removing the, RCD, problem solved.

21-02-2007, 09:55 AM
not a good idea to feed an a/c to RCD....especially inverters..........

Its the other way around - to drop the supply to the devices before an external surge/spike hits them.


22-02-2007, 03:55 AM
Careful with electric protections:
RCD: Residual Current Device: Detects difference in power going through Live & Neutral in other words leakage to earth, saves lives cutting out faulty equipement hopefully before it zaps the user that touches it. There are also 3 phase versions...and levels of sensitivity 30mA 300mA Some also detect DC (rectified power leakage) DO NOT REMOVE OR BRIDGE!

What you may be refering to are Over voltage/Spike protectors... come in many flavours and options: some cut the mains when voltage is too low or too high, others filter out spikes of 3000 + volts across lines or to earth (lightning strikes) you can get these from motors when disconnecting (sparks: and yes; A/C motors, fans and pumps are included but usually have some degree of suppression.)
These protectors are usually limited in terms of amperage they will allow enough through for a TV, PC, VDU printer but no more.
Very unlikely you can protect an A/C with one - hence my ranting about cheaply engineered air conditioners: they cut costs and reliability:mad:
(Note: I am not refering to Uninterruptable Power Supplies)

26-04-2007, 08:37 AM
Hi to everyone who was watching this thred, sorry, I, never replyed with how, I, got on, so here it is:

The transformers were at falt in this case, I, got hold of two new ones and replaced them and everything is working perfect now. After, I, had done this job, I, have been callded out to three other jobs with problems after taking a, power surge, and every job was the same problem the transformers.

Thanx to evreyone who helped on this one.


26-04-2007, 06:49 PM
Koy, thank you for the update, glad to hear that the problem is resolved.

The MG Pony
26-04-2007, 09:51 PM
Yes I was going to say often in power surge the primary of the transformer burns, that or relay contacts get carbonized and thus will allow insufficient current through.

Glad to see you got it nailed and congrats! It is good to see others helping thoughs who can't fully afford it! Props my friend!

27-04-2007, 04:27 PM
Hi reading the above especially Vikings comments gave me an idea, if the indoor fan is 240v and the condenser runs on 240v why not rip out all the elctronics and make it electro mechanical by installing a simple controller on / off and stat control.

When i was out on the road as a service engineer i always carried a room stat and 30 amp relay, got many sever rooms with splits and faulty PCB's in back on line that did as a temp repair. Making this permanent would probably lose most of its functions like louver motors fan speeds ect but would get his units working again cheaply. Just make sure the H/P L/P switches, comp thermal overload are wired in to the control circuit if this is viable.

Good luck