Fridge/freezer woes

[Grumps]

Hello All.

I've got a 20 year old Bosch frost-free f/f. A couple of times in the last fortnight (that I've heard), the unit has made what I can best describe as a loud pop, but continued to work. Now, the compressor starts (it doesn't sound quite right) and then stops after a few seconds accompanied by a small click. After about 1-2 minutes there is another click and the compressor starts again. This cycle repeats itself. Obviously it isn't maintaining the right temperature! Occasionally the motor will run and it can lower the temperature to -27C in several hours.

What I understand about the operation is this (from a bit of reading and looking at the motor start device on my compressor): Inside the compressor there are two coils, M(ain) and S(tart). When the controller demands more cold, then the C(ommon) is connected to L(ive). The M is permanently connected to N(eutral). M is connected to S via a disk thermistor by the looks of it. The thermistor cold resistance is about 30 Ohms. The hot resistance is several k. When the motor starts, effectively both M and S are energized, but S loses its power as the thermistor heats up.

But added to this there is the overload protection (which must be what's kicking in and start/stopping the motor). This device is in series with the C pin. There is also a 2.5uF cap across M and S. This measures at about 2.4uF with my trusty meter.

I've experimented and removed the thermistor. Obviously the motor just rattles and will not start as S has no power. If I short M to S the motor will start, and even if I remove the short when the motor is running, the overload protection cuts in. I have measured the resistance of the coils M-C, S-C, and M-S. The values are (about) 10 Ohms, 20 Ohms, and 30 Ohms (I might've got the M and S numbers the wrong way round), so this looks like the coils haven't got an issue.

So, what is the most likely cause of the problem:

1) Motor/Compressor bearings have gone tight and causing an overload? 2) The overload protection device has become too sensitive? 3) The thermistor isn't increasing resistance quickly enough?

I can get a genuine Bosch replacement for about £45. Or I can get a generic start relay for about £10. The Bosch part comes complete with the overload device too.

Any suggestions? Ta.

[Grumps]

That was another thought. But sometimes the motor will run and the temp does drop properly.

Reuse, repair, recycle. That's what kids are taught nowadays. I always like to try and fix things, but do see that sometimes there's no point flogging a dead (dying) horse. Ta.

[Dave Liquorice]

It's 20 years old, it doesn't owe you anything. Be thankful that being a frost free it has lasted as long has it has.

As to replacing the compressor is it not also plumbed into the refridgerent circuit? You'll have to collect the gas (in theory) and re-gas it with the right gas and amount. At twenty the actual fault may be loss of gas.

A modern one should be more effcient as well.

[Andrew Gabriel]

I had a freezer which started doing this. Compressor would start, you could feel the pipework just start to cool, and it would cutout.

I plugged it in via a power meter and found the compressor was pulling over 3kW continuously when running, hence the thermal trip cutting out. (Should have been about 100W.) Probably a shorted turn in the compressor, but that was the end of the freezer, which was over 10 years old.

[The Natural Philosopher]

The prroblem with an ld fridge is that really, they are not very sophisticated beats, and the whole lot was not only not built to a decent stndard 20 ears ago, but will have degraded.

I mean today we would expect instead of fully slumpable rockwool insulation, solid foam insulation, better door seals, a more efficient motor and in general better control of temperature.

If you do the cost benefit analysis on a new fridge freezer. say in the

400 quid mark? and work out how many units of electricity that represents, say 4,000, and work out how many hours there are in say 10 years - 87,000 - you can see that £400 equals either a new fridge, or about 45W for 10 years.

If you believe that the new fridge will 45W less power, or that electricity prices are likely to rise, or some admixture of the two, then its way better to spend 400 on a new fridge rather than £200 refurbishing an old one.

[Skipweasel]

Twenty years ago isn't as long as you think - I think!

Our fridge is nearly that and has foam insulation, decent door seals - though I can't speak for the quality of the motor and control gear, suffice to say that after being DOA and repaired and failed again and replaced, it has since been a stalwart. Oh, except for the silly condensation drain which keeps getting blocked.

[Grumps]

A new compressor (from Bosch) is £250. Then, as you indicate, there is a certain complexity of installing it and gas. So if I could get a repair man to fix it, it's going to cost about the same as a new f/f.

Indeed. Ta.

[Andrew Gabriel]

There was a window of a few years, around 25 years ago, when the closed cell CFC-expanded foam insulation was banned*, and a fibre matting was most often used. The fibre matting was not closed cell, and although covered in foil, it wasn't air-tight, and the insulation slowly became water/ice logged. This made the fridge/freezer horribly inefficient, and in the case of freezers, eventually start generating a puddle of condensate and fail to keep cold enough.

• The closed cell CFC-expanded foam insulation contained more CFC than the refrigerant, and the CFC wasn't easily recovered. The insulation was a fantastic long life thermal insulator though.

[Tabby]

The fault sounds like a shorted turn or a few on the compressor. This won't show up on a resistance test, its inductance that's significantly affected, hence excessive current draw. A replacement compressor costs a few quid from the tip or nothing on freecycle. If its R12 you wont be able to refill it with R12 legally, but a lot of R12 machines can run on - I can never remember whether its propane or butane, but google. As someone said, legally you're required to collect any scrap R12.

NT

[Mr Pounder]

Knacked compressor. The compressor for 45 quid is refurbished. It will cost you more that the f/f is worth to have it fitted. You can't do it unless you have the tools, brazing gear, a Schrader valve, the R12 drop in replacement refrigerant and the equipment to measure it. If you are a Scrooge look in your local paper for some poor sod who will come out to you without a call out charge. He will tell you the same as me.

Mr Pounder

[Jules Richardson]

Ours is 34 years old and I believe has some solid foam insulation in the side walls. Prices for something new of comparable size seem to be upwards of $1000, not the $400 that was mentioned, so the "break even" point is a lot further away. It gets even worse if I try to factor in the six months of the year up here that we're running the house heating, during which any heat lost by the fridge due to inefficiencies is still actually doing useful work.

It's extremely difficult to make a reliable estimate of where the break- even point is, but taking into account the above I figure it's probably about a decade at least, meaning that a modern fridge needs to last that long without an major repair costs. I'm not sure what warranties are like, but I suspect they don't go above five years - and I've looked around a few models at the store and the build quality doesn't seem particularly inspiring (the one that we have is built like a tank :-)

Of course sooner or later the compressor or something else major will fail on the current fridge, which will likely force me into replacement, but I'm not in any particular hurry otherwise.

cheers

Jules

[Jules Richardson]

The perils of reading two diy groups on both sides of the Atlantic - oops ;-) Still, 400 quid is around $600, I think, so it's still quite a bit more for us to replace what we have based upon the capacity.

cheers

Jules