Fixing A Fridge

[Onoff]

Any fridge / freezer experts on here?

Drunkenly said I'd take a look at an ice cream fridge.

Got so far today then beer got in the way...again...

It's a dual compressor, Italian job:

With the fridge unplugged I put the megger across L & N. Got 0 megohm doing an IR test.

There's two compressors, each with a 79.9uF and 12uF capacitor.

I disconnected both 79.9uF capacitors, which I'm assuming are the start capacitors. Still reading 0 megohm across L & N.

Each "start" capacitor reads just over 50uF so assuming they're duff. I've checked the meter against a known, good, 80uF capacitor.

Checked the mains lead which is a plug in, IEC connector type and that's all good.

 

[Blobber]

Thermostats? Never had much luck with fridge repairs personally

 

[Onoff]

Should have added it's tripping the RCD in the cu when plugged in.

 

[hotponyshoes]

If it's tripping the rcd I'd start by checking for any shorts in the wiring.

Mouse damage, or around any tie points as they can vibrate and rub through insulation.

After that, unplug anything internal that can easily be unplugged (compressor, fan) and see if it still trips

 

[piman]

Hello Onoff,

you are doing your test wrongly.
A megger tests insulation and the leads should be on one conductor and earth. That said unless you know the wiring you may still get a false reading.

Is it switched on when you plug it in, if so switch it off.
Personally I would look at disconnecting each compressor and any fan motor and test each individually. A damaged capcitor is usually evident by distortion.

Alec

 

[Onoff]

I think it's one of these:

 

[Onoff]

A damaged capcitor is usually evident by distortion.

Thanks. My tests on the two capacitors suggest they're "down" though? As I said I tested them both disconnected, discharged and against a known, good, 80uF capacitor.

 

[Onoff]

As an aside I did disconnect what I assume is R3, the frontal glass trim heater.

I presume that's just a resistance "wire"? End to end this one measured circa 12 ohms.

 

[knighty]

I'm fgas registered

Are you testing it at home or at their place?

2 compressors is a little weird but I've not seen many fridge counters in person

personally (and I know it's not the 'right' way to do it) and unplug as much as possible then plug it back in to test see if it still trips

if no trip... plug something back in and test again... then keep going like that


it would be rare for both compressors to die at the same time... but one could have died a while back so the other has been working twice as hard to keep up (and died)

are the condensers clean/clear? (hot radiator bit) - if they’re blocked the coprocessors will have been working much harder - higher temperatures and pressure does them no good

any signs of oil anywhere? (if the refrigerant leaks out you can normally see oil marks where oil had been carried out with it)

heaters are a pretty normal failure, controllers too, especially if they get wet

 

[Onoff]

Are you testing it at home or at their place?

At their place.

 

[hermetic]

megger test between live and earth, you should get a reading of near infinity if all is well, and as the RCD is tripping this indicates there is more current flowing down the live than is returning via the neutral, ie some is leaking to earth, start unplugging/disconnecting stuff and retest between each disconection and when the reading goes to or near infinity, of even changes significantly you have found the fault. Having said all this, I fear I agree with the above diagnosis that both compressors have failed as an overheat /seizure fault in the compressor motor causes insulation in the motor to overheat and fail, and thus create a current path to earth.

 

[Onoff]

Thanks all.

Before I go any further, are both these 79.9uF capacitors duff then at just over 50UF each?

I've measured hundreds of capacitors over the years btw.

 

[sg66]

My limited experience with fridge tripping is failed compressor

 

[Onoff]

I’ve never come across a capacitor of 79.9 anything! Most are not even quoted to 2 significant figures.

I hope there isn’t 240V across that heater!

How did that .9 get there? In my defence I had had a drink.

 

[Onoff]

I hope there isn’t 240V across that heater!

R1, 3, 4 & 5 are wired in parallel across the secondary of the transformer in the centre of the wiring diagram. I can't see what the secondary voltage is though (diagram too blurred).

 

[JimmyS]

If its tripping the rcd then presumably something is down to earth. I'd try and test the compressor windings with the megger to see if you have a goosed compressor or disconnect a compressor at a time and see if it trips. same with evaporator and condenser fans.

 

[knighty]

have you tried turning it on with the compressor and capacitor disconnected?

they could be a red herring

 

[Onoff]

Update on this:

I found a loose live wire, as in the screw was totally loose and the ring terminal flopping about. The live wire that goes to the top terminal in the foreground from the cable being pointed to:

Appears to supply L & N to the relay.

Tightened it up, switched on and the fridge fired up. The BG B20 RCBO (it wasn't an RCD), didn't trip.

Wondering tbh if this fridge should have it's own RCBO. They plug in a hot plate, toaster etc to the same circuit.

I have suggested a fridge alarm like this as a stop gap:

https://www.amazon.co.uk/COTINSE-Indicator-Adjustable-Monitoring-Refrigerators/dp/B0D9GKHNV1?

Back to my beer!

 

[Dave-sparks]

. The BG B20 RCBO (it wasn't an RCD), didn't trip.

An RCBO is an RCD

 

[Onoff]

An RCBO is an RCD

Erm no it's not...

An RCBO incorporates an RCD as well as an over current / over load device.