Really really annoying fridge fridge problem - any suggestions?

[ShinyShoe]

The fridge is only 5 years old and in summer works a treat. The back is kept clean and clear of dust and the icebox is clear of ice.

So not brand spanking new. So faults not impossible, including gas leaks. The summer bit is important I think! A fridge low on gas does not like summer at all. Of course this summer hasn't arrived yet!

I'm assuming the thermostat is in the main body of the fridge?

usually directly behind the knob you twiddle. But removing it may be from within or from outside the fridge.

Meanwhile I'll start a temperature log over the next day or so.

:opcorn::
Would be good to see what happens if you switch off the computer fan and / or put on some cabin heating too...

Yes I wonder what the dial is relative to? If say 1=8 degrees, 2=7 degrees etc then I'm not asking it to do very much by setting it to position 2!

I like your logic that 1=8C and 2=7C. I think if it was anywhere that reliable they might label them as such. 1 = warm, 8 = cold! Thats as good as you'll get! Its a mechanical stat with a bit of metal that contracts and expands and makes and breaks a circuit. It really isn't smart!

It certainly wont be in 1C increments. It probably isn't even a linear relationship. So 1 and 2 could have big jumps maybe 3C but 7 and 8 could have virtually no difference maybe 0.2C... And I suspect its all relative to the environment so 1 may be 10C lower than the room air... 2: 13C lower ...7: 18C lower ... 8: 18.2C lower but where the room air is measured is likely to be behind the fridge. The designers knew that would be warmer than normal... but you are making it cool with your fan... so on top of the existing issues with capillary tubes etc you are asking it to maybe be 13C lower than a 10C airspace so its trying to get to -3C. As it tries to get there the compressor heats that backspace a bit even with the PC fan. Maybe it gets to 15C. So now the fridge target is only 2C which is achievable. It achieves that and switches off the compressor. The internals of the fridge stays at maybe 2-3C for a bit. But your PC fan blows the warm air out and cold sea temp air in dropping the airspace to 10C again, making the thermostat think you want it at -3C again and so it starts the process of heating the back area again... The designers didn't factor in you blowing cold air through or they wouldn't be measuring relative to the back space...

Under normal conditions (in a house) the fridge is probably at 18C in the room and the back space at 25-30C. So setting it to number 2 might drop it to 12C inside the chamber, but it doesn't fluctuate that much even as the room heats and cools because the air isn't circulated.

 

[PaulRainbow]

So not brand spanking new. So faults not impossible, including gas leaks. The summer bit is important I think! A fridge low on gas does not like summer at all. Of course this summer hasn't arrived yet!

It works OK in the Summer. A fridge low on gas doesn't like any time of year.

:opcorn::
Would be good to see what happens if you switch off the computer fan and / or put on some cabin heating too...

It will make things worse if he disconnects the fan. The fan is fitted to assist in removing heat from the condenser. This is a common feature on fridges fitted to boats/motorhomes/caravans etc. Much the same way as keel coolers are used to dispose of the heat that has been removed from the cabinet.

The designers knew that would be warmer than normal... but you are making it cool with your fan... <snip> But your PC fan blows the warm air out and cold sea temp air in dropping the airspace to 10C again, making the thermostat think you want it at -3C again and so it starts the process of heating the back area again... The designers didn't factor in you blowing cold air through or they wouldn't be measuring relative to the back space...

The designers fitted the fan to draw air at ambient cabin temp across the compressor and through the condenser. Stopping the compressor from running at too high a temperature and assisting in the dissipation of heat from the condenser. Your description of how the stat and fan work are completely flawed. When the fridge reaches the set temp it switches the compressor off, shortly thereafter the fan will also switch off. The thermostat is also not set relative to the ambient temp, it is set to internal cabinet temp (or plate temp). Cooling the condenser with a fan does nothing to cause the stat to close.

Without the fan the compressor will run for even longer, as the heat from the condenser is not dissipated as quickly and it therefore takes longer to bring the cabinet temp down to the desired temp.

 

[ShinyShoe]

It works OK in the Summer. A fridge low on gas doesn't like any time of year.

Correct. But if its borderline on gas it will struggle a bit in winter and then struggle a lot in summer. It was fine last summer. We don't know about summer this year.

It will make things worse if he disconnects the fan. The fan is fitted to assist in removing heat from the condenser. This is a common feature on fridges fitted to boats/motorhomes/caravans etc.

I get why the fan has been fitted. BUT unless the description Colvic gives is wrong, he added a fan himself. So their may be two fans as reading the manual it appears there is an inbuilt fan

The designers fitted the fan to draw air at ambient cabin temp across the compressor and through the condenser. Stopping the compressor from running at too high a temperature and assisting in the dissipation of heat from the condenser.

Yes but they didn't install a PC fan, and Colvic makes no references to this being controlled by the fridge.

Your description of how the stat and fan work are completely flawed.

I wont argue with you on the stat. You seem to be claiming some knowledge of the specific bit of kit. I've never known a mechanical stat that didn't have a degree of effect caused by ambient temp.

Without the fan the compressor will run for even longer, as the heat from the condenser is not dissipated as quickly and it therefore takes longer to bring the cabinet temp down to the desired temp.

Unless the cold ambient temp is the cause of the problem what with the capillary tubes being reduced in side and the condensed liquid being more thixotropic etc.

 

[PaulRainbow]

I get why the fan has been fitted. BUT unless the description Colvic gives is wrong, he added a fan himself. So their may be two fans as reading the manual it appears there is an inbuilt fan

We both seem to be making different assumptions regarding the fan. I was assuming he was referring to the manufacturers fan, you assume he's fitted an additional one. Perhaps he can clear that up ?

Unless the cold ambient temp is the cause of the problem what with the capillary tubes being reduced in side and the condensed liquid being more thixotropic etc.

It's designed to work in ambient temp down to -10c, so i don't think that would be the case.

 

[ShinyShoe]

Someone asked about the stat... found this useful pictorial on replacing it:
https://www.leisureshopdirect.com/pdf/coolmatic_faultfinder.pdf

It looks as though the stat although not digital is not a simple bi-metalic switch but something a bit fancier.

There is an interesting line in there about the probe going into the pipe in the insulation... if it wasn't quite on the pipe I suspect that may cause these issues, i.e. you are measuring the temp of the insulation. But it would mean the chamber got +++ cold first?

That same document refers to ambient temp needing to be >16C as did a forum post I linked to before. But Mr Rainbow is right - the manual (section 7.1) says -10C as lower range (although I guess you could argue its working - just not at its most efficient!)

 

[PaulRainbow]

I'll post the temperature log in a couple of days.

Just note the temp when it switches off and time how long it stays off. Turn it to the lowest temp setting and repeat.

 

[LittleSister]

Also if the unit is old it could simply be that the compressor, likely a Matsushita Swing compressor, which is a simple Solenoid style piston with valve in the solenoid armature, is worn out.

Is replacing the compressor fairly straightforward? And if so, is it highly dependent on having the exact replacement.

I'm having similar problems to Colvic Watson on an oldish Waeco - the compressor is on an excessive amount of time. No problem with reaching the required temperature, even if that is very low. (The fridge is new to me, and I experimented with the aid of a digital thermometer with min/max to check it out and work out which way the thermostat control operated.)

 

[Rivers & creeks]

In the summer it works a treat, and I'll reconnect the extra fan for those months, the other nine months I'm clearly fighting physics but I'll be speaking to Waeco about the mod that their Aussie distributor is doing. Meanwhile the simplistic solution I've come up with is to order one of these http://www.ebay.co.uk/itm/122145625760?_trksid=p2060353.m1438.l2649&var=422239337262&ssPageName=STRK%3AMEBIDX%3AIT it means I can set the internal thermostat at the coldest setting and the 12v timer at 1 hour in 4. That will keep the fridge cool enough and the consumption down to 1.5Ah equivalent.

 

[superheat6k]

Is replacing the compressor fairly straightforward? And if so, is it highly dependent on having the exact replacement.

I'm having similar problems to Colvic Watson on an oldish Waeco - the compressor is on an excessive amount of time. No problem with reaching the required temperature, even if that is very low. (The fridge is new to me, and I experimented with the aid of a digital thermometer with min/max to check it out and work out which way the thermostat control operated.)

Assuming you can obtain a new compressor this is what the process is to do the job properly. As long as it is approx the for the same size fridge I would expect it should be OK ...

1 Attach a line tap valve an degas with a recovery unit (although many will simply vent the gas I cannot condone this). It is likely to be R134a but check the data plate, where the gas type should be clearly marked. The gas could be re-used, but hose losses will be considerable relative to the overall system gas volume. A small fridge will see very little recovered relative to the hose losses, and I would reckon on needing most of a full charge.

2 Cut the old compressor out on its pipes close to its body, then sweat out the pipe stubs from the original soldered joints.

3 Install the new compressor and silver solder the joints

Braze the hole where the line tap was fitted, then fit a schraeder valve on the original fill stub, or affix a fill stub to the suction pipe.

4 Attach the power cables

5 Pressure test and check for leaks - approx 15 Bar to be done properly ideally with dry nitrogen required.

6 Evacuate ideally to below 5 Torr

7 Charge plated weight of fresh refrigerant (this assumes the compressor comes with the necessary oil charge). If supplied dry then using a car recharge kit including the Oil might work, but check the oil content of the can is sufficient, and be aware cars mostly use PAG oil rather than POE oil used in most fridges.

Switch on and see if it works.

Obtaining pure R134a is becoming more difficult for non trade (F Gas) registered firms / individuals, but Halfords I think are still selling regas kits with oil included. The smallest commercial cylinders are at least 3 kg and most are 12 kg. Your fridge will likely require ~ 0.3 kg possibly less.

If I were doing this I would expect the whole process to take just over half a day allowing for a 1 hour pressure test and 1 hour evacuation. But to do properly will require appropriate tooling, that most will simply not possess - recovery unit and cylinder, gauge manifold set, R134a and low weight fridge gas scales, vac pump, pressure manifold, oxyacetylene for the brazing, or possibly MAPP gas torch. DO NOT USE OXYGEN TO PRESSURE TEST.

You can see that without the right kit doing this is not straightforward. The tasks at items 1 & 7 should only be tackled by an F Gas registered engineer suitably equipped, otherwise the person doing this is breaking the law.

If you can find the compressor then a trip to your local fridge repair shop might be a better answer. Many small kit fridge guys will likely skimp on the pressure test and only vac down for ~20 minutes, and most will use their experience to judge whether pressure is needed, although only by a pressure test can the system be properly checked as clear of leaks. Evacuation is essential, so do not accept an offer to blast through with refrigerant instead of evacuation. Those who do offer this will have a rail outside where they tie up their horse.

 

[LittleSister]

Assuming you can obtain a new compressor this is what the process is to do the job properly . . . .

I'll interpret that as 'just go and buy a new fridge'!

Thanks for taking the trouble to explain it all. I certainly wouldn't attempt anything like that myself, and guess the cost of getting it done properly would approach that of replacing the fridge, but your description improves my limited understanding of what is going on in that mysterious pile of gubbins in the back.

I look forward to trying out the rough and ready test checks you outlined in your previous post, and keep my fingers crossed all is well.