How to tell if fridge compressor needs re-gassing

[MattS]

I have a converted coolbox -> fridge on my Moody 28. I've just got the compressor running again after replacing the control unit, which seemed to have given up the ghost.

It now runs properly, but I'm struggling to get the coolbox down below 11C when it's 25C outside, which is clearly not cool enough to be useful.

I know insulation is likely to be one culprit (it is insulated with thick foam etc.)

How does one tell if they're compressor system needs re-gassing? Are there any obvious telltale signs or tests I can do?

 

[Bilgediver]

The best test is to measure the pressure in the system. Watch this video and if you are lucky your system will have a similar charging point so accept the adaptors for cars.

 

[MattS]

The best test is to measure the pressure in the system. Watch this video and if you are lucky your system will have a similar charging point so accept the adaptors for cars.

Thanks. I think it does have a charge port on top - will take a look. Didn't realise you could buy kits to do this yourself including pressure gauge, so that's useful to know too!

 

[Spirit (of Glenans)]

The best test is to measure the pressure in the system. Watch this video and if you are lucky your system will have a similar charging point so accept the adaptors for cars.

Very useful post.

 

[vas]

I think an easier way is to check (after it's running for sometime) how far is the evaporator plate frozen.
a couple of points/Qs:
When you say doesn't go lower than 11C (indeed useless even for beer!) is the compressor running constantly? or could it simply be the thermostat is broken/wrongly setup?
is the fridge getting decent cool air at the compressor area? is the fan running?
is the air somehow extracted from there or stuffed?
if you can pull the compressor assembly to a more "open" space with better ventilation, do it temporarily and see if fridge cools better.

V.

 

[MattS]

I think an easier way is to check (after it's running for sometime) how far is the evaporator plate frozen.
a couple of points/Qs:
When you say doesn't go lower than 11C (indeed useless even for beer!) is the compressor running constantly? or could it simply be the thermostat is broken/wrongly setup?
is the fridge getting decent cool air at the compressor area? is the fan running?
is the air somehow extracted from there or stuffed?
if you can pull the compressor assembly to a more "open" space with better ventilation, do it temporarily and see if fridge cools better.

V.

Yes sorry that was with the compressor running constantly for 4 hours last night. The fan is definitely running for the whole time. The evaporator plate is definitely frozen in places, but I'll pay more attention to how - what am I looking for there?

I think it might be getting quite warm around the compressor, as it's within cabinetry underneath the actual cool box, and there isn't great air flow with the cupboard doors closed. I'm not sure how quickly the ambient temp affects the compressor efficiency? But I also wondered whether the general heating up of the space under the coolbox is just translating straight back into warming of the coolbox...

Moving compressor not that easy as the base plate has basically rusted away, so when I eventually get it out it might not go back in... however I did think about opening the cupboard doors and sticking a big fan pointing into the cupboard to create a big old airflow...

 

[vas]

I've spent too many hours trying to sort out my galley fridge (the second one in the salon is fine!)
if you have an IR thermometer, start hitting the evaporator from one end to the other, you'll notice a drop of temp (or rise if you start on the wrong side ) note temps, ideally it should all be rather constant and minus little (don't remember offhand now) so do that as a first check
IIRC not being able to sustain the temp is an indication.

However, having the compressor in an unventilated spot is a recipe for disaster, tbh I wouldn't look at fixing anything before bringing decent fresh and cool air (from the bilges below, from outside) to the compressor assembly and the fan there.
V.simple to open the cupboards and get a big fan, do it and check temps in the fridge. I bet it will be closer to 4C within a few hours.

V.

 

[vyv_cox]

There is a page on my website that answers your question Recharging marine refrigeration systems

 

[MattS]

I've spent too many hours trying to sort out my galley fridge (the second one in the salon is fine!)
if you have an IR thermometer, start hitting the evaporator from one end to the other, you'll notice a drop of temp (or rise if you start on the wrong side ) note temps, ideally it should all be rather constant and minus little (don't remember offhand now) so do that as a first check
IIRC not being able to sustain the temp is an indication.

However, having the compressor in an unventilated spot is a recipe for disaster, tbh I wouldn't look at fixing anything before bringing decent fresh and cool air (from the bilges below, from outside) to the compressor assembly and the fan there.
V.simple to open the cupboards and get a big fan, do it and check temps in the fridge. I bet it will be closer to 4C within a few hours.

V.

That will be my next step!

There is a page on my website that answers your question Recharging marine refrigeration systems

Thanks Vyv - I'm going to take a good read of that!

 

[superheat6k]

But the problem with Vyv's page is that to follow it you are likely breaking the law ! Boat based refrigeration or air-conditioning systems are not classed as mobile systems, as suggested - this means cars, vans, and other motor vehicles - it does not mean boats where the systems are installed, and it does not mean ever refrigeration. But I'll just leave that there.

However, the OPs issue is a high evaporating temperature, so just chuck a load more gas in ! Or perhaps not.

So perhaps there is to much in already - yes it can very easily happen.

Too much gas equates to a higher suction pressure to the compressor - so what ?

So as the pressure increases so does the boiling temperature (aka technically as Saturated Evaporating Temperature or SET) of the refrigerant and with it so does the resultant surface temperature of the evaporator plate, as this temperature increases so does the effective space temperature your fridge is able to achieve.

So adding gas does have a finite limit, but seemingly always on here all problems with fridges are diagnosed as it's 'short of gas' !

Another factor is that the higher the temperature affecting the condenser (NB not the compressor), the higher the discharge pressure, so the higher the boiling point again (this time the Saturated Condensing Temperature SCT). But and importantly the flow through the capillary is a function of the inlet pressure so push this up = more flow = more suction pressure = higher SET = higher evaporator plate temperature. However, often the condenser resides close to the compressor and getting the heat away from the compressor and condenser is the essential requirement, so cooling the compressor does help the condensation phase.

My advice here is to increase the compressor and condenser ventilation, and check the system is not overcharged.

I regret I shall not agree to Vyv's illegal method of releasing refrigerant into the atmosphere, and TBH I am amazed he still promotes this nonsense in 2022, when venting of refrigerants became illegal in the 1990's.

Finally confirm that you are using pure R134a, and without added oil, especially as the only form of R134a Joe Public can buy in the UK is in the aerosol form which includes a considerable amount of oil. Bang this into your system and you will also be banging in a whole extra load of oil. Add to this a possible background leak and keep adding more, so the gas is leaking out, but the oil isn't, just increasing the volume of oil present. Oil is great at lubricating compressor bearings, but too much of it is very adverse for the system refrigeration itself.

 

[LittleSister]

While Vyv's page might benefit from being updated to make clear that the 'new' UK regulations are now in place, I find the explanation of normal operation and fault identification very useful to me.

The description of the method of recharging would presumably be very useful for those cruising or otherwise based in other jurisdictions, especially in situations where professional assistance with knowledge of marine systems is unavailable.

Vyv's whole site is a fantastic resource, and I think he should be applauded for the care and effort that he's put into it. In that context by all means encourage and assist him to continue to refine, expand or update it if he's willing to do so, but I'd hate for him to perceive suggestions or expressions of differing opinions as attacks on himself or his excellent creation.

 

[vyv_cox]

But the problem with Vyv's page is that to follow it you are likely breaking the law ! Boat based refrigeration or air-conditioning systems are not classed as mobile systems, as suggested - this means cars, vans, and other motor vehicles - it does not mean boats where the systems are installed, and it does not mean ever refrigeration. But I'll just leave that there.

However, the OPs issue is a high evaporating temperature, so just chuck a load more gas in ! Or perhaps not.

So perhaps there is to much in already - yes it can very easily happen.

Too much gas equates to a higher suction pressure to the compressor - so what ?

So as the pressure increases so does the boiling temperature (aka technically as Saturated Evaporating Temperature or SET) of the refrigerant and with it so does the resultant surface temperature of the evaporator plate, as this temperature increases so does the effective space temperature your fridge is able to achieve.

So adding gas does have a finite limit, but seemingly always on here all problems with fridges are diagnosed as it's 'short of gas' !

Another factor is that the higher the temperature affecting the condenser (NB not the compressor), the higher the discharge pressure, so the higher the boiling point again (this time the Saturated Condensing Temperature SCT). But and importantly the flow through the capillary is a function of the inlet pressure so push this up = more flow = more suction pressure = higher SET = higher evaporator plate temperature. However, often the condenser resides close to the compressor and getting the heat away from the compressor and condenser is the essential requirement, so cooling the compressor does help the condensation phase.

My advice here is to increase the compressor and condenser ventilation, and check the system is not overcharged.

I regret I shall not agree to Vyv's illegal method of releasing refrigerant into the atmosphere, and TBH I am amazed he still promotes this nonsense in 2022, when venting of refrigerants became illegal in the 1990's.

Finally confirm that you are using pure R134a, and without added oil, especially as the only form of R134a Joe Public can buy in the UK is in the aerosol form which includes a considerable amount of oil. Bang this into your system and you will also be banging in a whole extra load of oil. Add to this a possible background leak and keep adding more, so the gas is leaking out, but the oil isn't, just increasing the volume of oil present. Oil is great at lubricating compressor bearings, but too much of it is very adverse for the system refrigeration itself.

You are correct of course, it is some time since this page was updated. It is intended as a guide to the observable symptoms of refrigerator faults rather than an instruction to the DIY user.

 

[vyv_cox]

While Vyv's page might benefit from being updated to make clear that the 'new' UK regulations are now in place, I find the explanation of normal operation and fault identification very useful to me.

The description of the method of recharging would presumably be very useful for those cruising or otherwise based in other jurisdictions, especially in situations where professional assistance with knowledge of marine systems is unavailable.

Vyv's whole site is a fantastic resource, and I think he should be applauded for the care and effort that he's put into it. In that context by all means encourage and assist him to continue to refine, expand or update it if he's willing to do so, but I'd hate for him to perceive suggestions or expressions of differing opinions as attacks on himself or his excellent creation.

Thank you very much for your kind words, much appreciated.

 

[MattS]

But the problem with Vyv's page is that to follow it you are likely breaking the law ! Boat based refrigeration or air-conditioning systems are not classed as mobile systems, as suggested - this means cars, vans, and other motor vehicles - it does not mean boats where the systems are installed, and it does not mean ever refrigeration. But I'll just leave that there.

However, the OPs issue is a high evaporating temperature, so just chuck a load more gas in ! Or perhaps not.

So perhaps there is to much in already - yes it can very easily happen.

Too much gas equates to a higher suction pressure to the compressor - so what ?

So as the pressure increases so does the boiling temperature (aka technically as Saturated Evaporating Temperature or SET) of the refrigerant and with it so does the resultant surface temperature of the evaporator plate, as this temperature increases so does the effective space temperature your fridge is able to achieve.

So adding gas does have a finite limit, but seemingly always on here all problems with fridges are diagnosed as it's 'short of gas' !

Another factor is that the higher the temperature affecting the condenser (NB not the compressor), the higher the discharge pressure, so the higher the boiling point again (this time the Saturated Condensing Temperature SCT). But and importantly the flow through the capillary is a function of the inlet pressure so push this up = more flow = more suction pressure = higher SET = higher evaporator plate temperature. However, often the condenser resides close to the compressor and getting the heat away from the compressor and condenser is the essential requirement, so cooling the compressor does help the condensation phase.

My advice here is to increase the compressor and condenser ventilation, and check the system is not overcharged.

I regret I shall not agree to Vyv's illegal method of releasing refrigerant into the atmosphere, and TBH I am amazed he still promotes this nonsense in 2022, when venting of refrigerants became illegal in the 1990's.

Finally confirm that you are using pure R134a, and without added oil, especially as the only form of R134a Joe Public can buy in the UK is in the aerosol form which includes a considerable amount of oil. Bang this into your system and you will also be banging in a whole extra load of oil. Add to this a possible background leak and keep adding more, so the gas is leaking out, but the oil isn't, just increasing the volume of oil present. Oil is great at lubricating compressor bearings, but too much of it is very adverse for the system refrigeration itself.

I’m very grateful for all replies and contributions to my question, of course - so thank you for taking the time to reply and your added explanation.

However you have essentially repeated the core points of previous replies and from Vyv’s site, which does make enough mention of the UK’s regulations for me to make my own choices and importantly gain knowledge that I don’t have already, so I do feel you could have been a little more respectful to the value of others’ contributions rather than just criticising it as a side-swipe. Sites like Vyv’s save boaters ££££s over the lifetime of boat ownership. I do wish we could be a bit more diplomatic about this stuff.

 

[Daverw]

You may need to understand that superheat6k like myself is a refrigeration engineer, we have had to over the last years jumped through many regulatory hoops and seen much miss use of refrigerants that have clearly damaged our planet The situation is getting better within our industry over time but we are very heavily regulated. Luckily for me I work with natural refrigerants such as ammonia and C02 which dont harm the plant will very easily kill you.
the small quantities of refrigerants used in boats is low but many refill very often with the gas going up into the sky

 

[superheat6k]

While Vyv's page might benefit from being updated to make clear that the 'new' UK regulations are now in place, I find the explanation of normal operation and fault identification very useful to me.

The description of the method of recharging would presumably be very useful for those cruising or otherwise based in other jurisdictions, especially in situations where professional assistance with knowledge of marine systems is unavailable.

Vyv's whole site is a fantastic resource, and I think he should be applauded for the care and effort that he's put into it. In that context by all means encourage and assist him to continue to refine, expand or update it if he's willing to do so, but I'd hate for him to perceive suggestions or expressions of differing opinions as attacks on himself or his excellent creation.

I agree the rest of Vyv's site is an excellent point of reference, save the bit about refrigeration, and to suggest other regions, would exclude the whole of Europe, where the rules of venting refrigerants originated from.

 

[superheat6k]

I’m very grateful for all replies and contributions to my question, of course - so thank you for taking the time to reply and your added explanation.

However you have essentially repeated the core points of previous replies and from Vyv’s site, which does make enough mention of the UK’s regulations for me to make my own choices and importantly gain knowledge that I don’t have already, so I do feel you could have been a little more respectful to the value of others’ contributions rather than just criticising it as a side-swipe. Sites like Vyv’s save boaters ££££s over the lifetime of boat ownership. I do wish we could be a bit more diplomatic about this stuff.

Not a side swipe - the legal situation that a professional industry, that I am a part of is trying our hardest to follow.

Amazingly people will agree it is completely unacceptable to dump oil from the bilge into the water, or to throw rubbish overboard, but because refrigerant gases can't be seen that doesn't matter.

Well I am afraid it does.

And I will not cease in my objections. SO yes generally Vyv's advice is invaluable, but for this aspect it does require an update.

 

[vyv_cox]

Not a side swipe - the legal situation that a professional industry, that I am a part of is trying our hardest to follow.

Amazingly people will agree it is completely unacceptable to dump oil from the bilge into the water, or to throw rubbish overboard, but because refrigerant gases can't be seen that doesn't matter.

Well I am afraid it does.

And I will not cease in my objections. SO yes generally Vyv's advice is invaluable, but for this aspect it does require an update.

I have modified it but Owen, who is a registered refrigerant engineer, points out that in the case of overfilling there is no practical possibility for the DIY owner to resolve it.
The only other alternative is to remove the page altogether, which would be a poor solution as people find the diagnostic content useful.

 

[superheat6k]

I have modified it but Owen, who is a registered refrigerant engineer, points out that in the case of overfilling there is no practical possibility for the DIY owner to resolve it.
The only other alternative is to remove the page altogether, which would be a poor solution as people find the diagnostic content useful.

Vyv

Look I know your site is excellent, but this area is really difficult to offer sound advice presently.

Perhaps simply remove the bit about venting, with advice that excess gas should be properly decanted with a recovery unit to avoid atmospheric polution, and that professional assistance to do this might be necessary.

 

[vyv_cox]

Vyv

Look I know your site is excellent, but this area is really difficult to offer sound advice presently.

Perhaps simply remove the bit about venting, with advice that excess gas should be properly decanted with a recovery unit to avoid atmospheric polution, and that professional assistance to do this might be necessary.

Thanks. Maybe that's the answer.