How to tell if fridge compressor needs re-gassing

[superheat6k]

I simply give up

 

[KAM]

Just thought I'd add my bit. I installed a Waeco fridge system in my cool box about 8 years ago. A couple of years later it was not cooling very well. I though it might be the self sealing couplingd. No ice at all on the cooling plate. I bought some gas I think it came from Lithuania. Re gassed it once judging the amount by the degree of frosting on the plate. It took very little gas only a few seconds fill. Its worked perfectly since then. I've never understood why it started to fail shortly after installation. The self sealing couplings don't seem to be leaking. I thought it would be contaminated with moisture and need a full vacuum and refill but it just seems to work now. Pity the Waeco thermostat is so poorly marked.

 

[vas]

I'm not a refreg engineer, just a plain engineer with a bit of common sense.
I find it odd to go for a recharge when plate is frosting and at the recommended temp while you haven't sorted provision of cool air to the condenser and a way to remove the warm air produced to the outside (or bilge again....)
good luck

V.

 

[MattS]

So have done lots more experiments, thought I'd update the thread even if it's just for future readers struggling with the same problem!

@Daverw kindly visited me at Chatham and helped check the gas levels, which only required a very small top up.

Then, having put some bottles and cans in the fridge, so that it wasn't empty, I've left it for a decent amount of time to see how it can perform at getting the temperature down.

I have also had a separate fan positioned in the cupboard pulling air out from around the compressor and into the cabin, with both cupboard doors wide open - so I think the airflow around the compressor is about as good as you could expect it to get located in any locker. There is also a cut out in the bulkhead behind the compressor unit which goes into the space under the cooker and should be a route for cool air to be pulled in.

I also put some neoprene seal tape around the lid, which had no airtight seal. It won't be completely airtight, but would imagine it's making a significant difference to the lid seal now.

I then left a bluetooth temp monitor in the fridge itself which I can monitor without opening the fridge. Having run the fridge on full pelt for several days, I can see that even with the compressor running constantly, it is clearly struggling to keep on top of the temperature. I monitored it for 2 days in a row



Clearly it manages to get the temp down a bit overnight, but as soon as the ambient starts heating up during the day it can't keep on top of it and the temp in the cool box just creeps up again. This is with the compressor running 100% duty cycle. The evaporator plate seems to get to between -1 and -3C across the plate, but no lower.

Getting the phone camera in under the fridge, I can see that the insulation is not complete. No idea if this is the original insulation, but I guess it could well be. There are some notable gaps, in particular around the drain where the bare fibreglass is still exposed, and also up two corners of the fridge where pipework runs down and I presume it wasn't possible to get insulation into the space, or move the pipework.






I have read that it's good practice to tape up the gaps between the insulation as well, which hasn't been done.

On the external surface around the drain, I can feel condensation, which suggests to me it's probably also between the insulation and the fridge external surface etc.

There is also clear condensation on the cold pipe coming out of the compressor (not sure what the proper name is!) and also on the white coiled pipe work that runs to the fridge, and that seems to just remain there constantly - certainly there's lots of evidence of it in the bilge.



There's also a hole internally where the pipework to the evaporator plate runs, which has been left open and filled with spray foam - and that spray foam is just soaking up condensation running off the bottom of the evaporator plate and down the pipe.



And using a cheapish thermal camera attachment for my phone, I can make out some clear warm spots inside the fridge, in particular in the corners and around the drain.





And this shows the evaporator plate (black = cold) next to the corner of the fridge, which seems to be a warm spot. This is one of the corners behind which the water tank filler pipe runs, so I expect there is no insulation down that corner at all.




I've also noticed that the control unit for the compressor gives us a fair bit of heat (50C measured using a thermometer gun) when it's been running for a while, so that plus the condenser being located immediately underneath the fridge is just exacerbating the issue of the poor insulation.

So all in all - I think I might be fighting a bit of a losing battle all the time there is significant heat transference into the fridge, even if I were to optimise the running of the compressor. Which is unfortunate! It might be fine in the winter...

 

[ashtead]

Had you considered if anyone on the moody owners forum has had the same issue and a solution. We have have had our fridge regassed a couple of times makes some difference but main issue is lack of cooling area around unit in hot weather . The problem we find is using the cupboards around the unit ie under the fridge and bunk as lack of air access for hot weather. I feel a keel cooled fridge might be way to go or buy a cheap separate box to keep beers cold from a decathlon place . We bought one in carrefour runs off the 5 amp socket and while a little noisy can be a useful back up.

 

[vyv_cox]

Had you considered if anyone on the moody owners forum has had the same issue and a solution. We have have had our fridge regassed a couple of times makes some difference but main issue is lack of cooling area around unit in hot weather . The problem we find is using the cupboards around the unit ie under the fridge and bunk as lack of air access for hot weather. I feel a keel cooled fridge might be way to go or buy a cheap separate box to keep beers cold from a decathlon place . We bought one in carrefour runs off the 5 amp socket and while a little noisy can be a useful back up.

Sounds similar to our Sadler. The air flow to the condenser was ridiculous, though a grill with slats the wrong way! Amazing that it worked at all, but it was only ever in northern European waters. It would have stood no chance in the Mediterranean.

 

[vas]

I then left a bluetooth temp monitor in the fridge itself which I can monitor without opening the fridge. Having run the fridge on full pelt for several days, I can see that even with the compressor running constantly, it is clearly struggling to keep on top of the temperature. I monitored it for 2 days in a row

View attachment 142076 View attachment 142075

Clearly it manages to get the temp down a bit overnight, but as soon as the ambient starts heating up during the day it can't keep on top of it and the temp in the cool box just creeps up again. This is with the compressor running 100% duty cycle. The evaporator plate seems to get to between -1 and -3C across the plate, but no lower.

since no one commented on that, I have to note that -1 -3C is NOT the right temp for the evaporator. that should be lower than -15C iirc. Looks like something in the system is not right. For comparison this is my setup, salon fridge works fine, galley fridge is always trailing and generally demoted to drinks fridge configured to run (CN digital thermostats on both) at 2C more than the salon one. The top line is ambient temp in the cabin, values last two days I'm away from the boat, boat locked and minimal ventilation due to the layout of windows and possiblity of rain.


note how compressor runs more and more as the day progresses and ends up running constantly from 16:00-20:00 not managing to drop the temp a tiny bit more (fraction of a C) for the compressor to stop. When ambient drops to 25C, things are fine (until ambient ups again) Thermostat delta is iirc 1.5C.

so, compressor/condenser/evaporator/filter combo is not OK. Not much point trying to seal the thing as long as evaporator is at -1C! (assume evaporator measurement taken with IR gun thermometer)

cheers

V.

 

[vas]

and a 6h interval (midday to midnight) that demonstrates also the worse insulation of the galley fridge: note how sharply the temp rises when the compressor stops compared to the salon one!


attrocious duty cycle on the galley one

ah, both fridges are 80lt front loaders, new magnetic seal on the galley one, minimal difference...
V

 

[MattS]

Had you considered if anyone on the moody owners forum has had the same issue and a solution. We have have had our fridge regassed a couple of times makes some difference but main issue is lack of cooling area around unit in hot weather . The problem we find is using the cupboards around the unit ie under the fridge and bunk as lack of air access for hot weather. I feel a keel cooled fridge might be way to go or buy a cheap separate box to keep beers cold from a decathlon place . We bought one in carrefour runs off the 5 amp socket and while a little noisy can be a useful back up.

I have MOA forums are an amazing resource, and are always a first port of call. There's lots of previous threads of people tackling these issues, but sometimes I find you can get a much wider pool of knowledge from YBW where an issue is not specifically a Moody one

As an aside, the reason I'm tackling this whole issue now is actually because I did the last year with an electric coolbox instead of using the fridge, which I found to be highly energy inefficient (vs actual cooling efficacy), and in the end it melted the 12v plug and socket - so I returned it for a refund! I discovered these issues with my fridge through trying to get that going again after a year of not using it...

Sounds similar to our Sadler. The air flow to the condenser was ridiculous, though a grill with slats the wrong way! Amazing that it worked at all, but it was only ever in northern European waters. It would have stood no chance in the Mediterranean.

In my various experiments, having air flow has definitely helped slightly, so at the very least I intend to create some vents into the space where the compressor is located either by putting vents on the cupboard doors, or possibly running an extraction fan type tube to a vent on the outside of the cupboard under the sink to really direct the airflow.

 

[MattS]

since no one commented on that, I have to note that -1 -3C is NOT the right temp for the evaporator. that should be lower than -15C iirc. Looks like something in the system is not right. For comparison this is my setup, salon fridge works fine, galley fridge is always trailing and generally demoted to drinks fridge configured to run (CN digital thermostats on both) at 2C more than the salon one. The top line is ambient temp in the cabin, values last two days I'm away from the boat, boat locked and minimal ventilation due to the layout of windows and possiblity of rain.

View attachment 142313
note how compressor runs more and more as the day progresses and ends up running constantly from 16:00-20:00 not managing to drop the temp a tiny bit more (fraction of a C) for the compressor to stop. When ambient drops to 25C, things are fine (until ambient ups again) Thermostat delta is iirc 1.5C.

so, compressor/condenser/evaporator/filter combo is not OK. Not much point trying to seal the thing as long as evaporator is at -1C! (assume evaporator measurement taken with IR gun thermometer)

cheers

V.

Yes - evaporator temperature taken with an IR gun.

and a 6h interval (midday to midnight) that demonstrates also the worse insulation of the galley fridge: note how sharply the temp rises when the compressor stops compared to the salon one!

View attachment 142314
attrocious duty cycle on the galley one

ah, both fridges are 80lt front loaders, new magnetic seal on the galley one, minimal difference...
V

That does seem to climb quickly. I presume your compressor is running for the time during which the temperature is being brought down, and is then off during the steep climb up until it starts falling again?

 

[Daverw]

-18 for a fridge is too low and will build ice up quickly which reduces capacity of system, for an internal temp of +4, would aim for an evaporatoring temp of -10 which gives an approx. 12 degree superheat, the plate temp will vary along its flow path and is difficult to actually measure accurately. I think Matts issue is a tired compressor which has worn valves and hench is not pumping very well under load. This you would normally test this on larger compressors with a pump down test but not really possible on such small systems as no isolation valves are fitted.

 

[vas]

That does seem to climb quickly. I presume your compressor is running for the time during which the temperature is being brought down, and is then off during the steep climb up until it starts falling again?

exactly if you compare the two, it's obvious that the galley one is inefficient, working overtime and "loosing" temp v. quickly. Still even with the compressor running effectively 24/7 during August I was fine with the 304Ah@24V lifepo4 pack, so not complaining much