Fridge not cold enough

[bcboomer]

Our fridge started defrosting itself about a week ago and now won't keep ice cubes frozen. It is a typical box style evaporator, (Vitrifrigo) with a Danfoss BD35 compressor.
One corner, where the thermostat sensor is, gets frosted but not the rest.
It has an additional circuit board added to the Danfoss control that I can't identify. It's the little yellow board in the attached picture and I'm not sure about it.
There are no fault codes generated and the compressor cycles approximately 3 minutes on then 3 minutes off.
The condenser doesn't get very warm, no signs of leaking R134 at the only pair of connections that I can see.

[chad-wl]

One corner, where the thermostat sensor is, gets frosted but not the rest.

I talked to the fine people at Nova Kool last month, since we had the opposite issue, where the entire box, and all the lines would frost up, and then it would run non stop.

That issue was caused by too much refrigerant and solved by bleading some off.

They said that the opposite issue would cause what you're seeing, a small section frosting only, probably by the small orifice that it is the icebox.

I would consider calling someone to remove and weight the coolant and check you're not loosing some.

[bcboomer]

It seems consistent with a low charge is possible but it would have to be a very small leak since it's been fine for 4 years and there is no sign of an oil leak.

[Anna Sail]

That yellow board on the bottom of your controller is a manual speed board. The Danfoss 35 (and 50) compressor is multiple speed and some systems (for example Sea Frost and Frigoboat) allow you to take advantage of these different speeds to save energy. As I recall, Vitrifrigo should be run at a minimum of 2500 rpm and it looks like that is what your thermostat wire is plugged into. The other wire from your Thermostat is plugged into the 'C' terminal (common). This would have little to do with your system running 3 minutes on 3 minutes off. Instead, it may indicate you have a leaky seal. If your compressor gets your box down to the set point, but 3 minutes later the box is now 2 degrees above that set point, then the compressor is going to come on again to bring it down, which it can do in 3 minutes. I see a pattern. If the reason is low refrigerant, you will need to find the leak first. However, low refrigerant would mean it would take quite a long time just to get the box down to the set point. And I suspect more than 3 minutes to bring it back down the two degrees to the set point (most thermostats have a 2 degree differential; maybe yours has been adjusted to a 1 degree....)

[bcboomer]

Thanks Anna Sail, that's good information. I don't see any adjustment on the thermostat. It's a plain Danfoss one.
The only connection I see doesn't show any oil or dust. Could a plugged venturi tube cause this?

[rancher44]

I had the same problem and had to replace the fan at the compressor .
Good Luck

[bcboomer]

The little pancake fan is happily whirring away. I've bypassed the 'stat and it still isn't cold enough.

[skipgundlach]

I think a seal problem would have fully frosted plates before cycling, but accumulate LOTS of ice quickly.

If you a have a keel-cooled unit, there are two connections for that part, two for the evaporator, and two for the compressor, which (I don't know your system) might have an air cooled element, which likely if original, would be integral to the compressor via fabricated vs quick-disconnect fittings.

It's still possible - particularly if it's sat for a while - to have some leakage without oil at the quick-disconnects; the oil would only be present in aerosol circulation (which should eventually show up as an oily feel to the quick-disconnect.

If you have the means and know how to keep it clean, adding a little refrigerant to see if the cold part gets bigger would tell you if you were undercharged. If you were, just add a bit at a time, over minimum hours, maybe a day, separation each time. Leave your can (shut) and hose attached until you see a change so you don't have to purge the line each time, and then open the valve to add - perhaps 15 seconds at a time, using that gauge to see what to do the next time (tiny bit of improvement? go 30 seconds the next time), etc.

You aren't, nearly certainly, overcharged. But if the above eventually puts you in that place (exit line frosts outside the box), you can bleed hygienically the same way by loosening your connection at the tap end (on the can, not on the compressor) for a second or two per event, waiting and seeing the change again, until the frost recedes to the edge of the exit.

Regardless, however, good seals are crucial if for no other reason than to lengthen time between defrost...

[Ndavies]

Agree with the other posts - it sounds like low refrigerant. My fridge system likely has a small leak, but its so small that it needs a minor top-up about every 2 years. If your system is R134a, I would try adding the smallest amount and see if it makes a difference. You can buy R134a with stop leak at an autoparts store. You will likely also need an adaptor to convert the shrader valve to a quick-fit (also from aotoparts store). Add the smallest amounts, run the system and look for a change... If you have an infrared thermometer, you can check for changes very quickly.
Neil

[skipgundlach]

Originally Posted by Ndavies

Agree with the other posts - it sounds like low refrigerant. My fridge system likely has a small leak, but its so small that it needs a minor top-up about every 2 years. If your system is R134a, I would try adding the smallest amount and see if it makes a difference. You can buy R134a with stop leak at an autoparts store. You will likely also need an adaptor to convert the shrader valve to a quick-fit (also from aotoparts store). Add the smallest amounts, run the system and look for a change... If you have an infrared thermometer, you can check for changes very quickly.
Neil

DO NOT PUT ANYTHING BUT PURE 134a IN THAT UNIT!!!!

[skipgundlach]

because the stop leak or anything else will thoroughly and permanently close the cap tube, leading to failure....

[bcboomer]

It's an air cooled system and has been in full time operation for the past 4 years.
Unfortunately it doesn't have an access port. The installation manual refers to poppet valves installed in both halves of the pre-charged system so I don't know what I would use to add R134a.

[Richard Kollmann]

Bcboomer, Little or no frost on evaporator is because compressor cycling every 3 minutes.
Low or no refrigerant will not stop compressor ever. Yes, too much refrigerant will stop compressor do to high amperage producing a 3 flash LED code.

I do not see where trouble code LED is connected to module D terminal. Is there a trouble LED installed on this system? If trouble LED is there and not flashing trouble must be in thermostat or speed resistor yellow plate. To eliminate thermostat and speed gadget unplug yellow plate from module and place a jumper wire across module terminals C and T. Compressor will run now at minimum 2000 Rpm.and cool box.

[bcboomer]

I didn't have the LED connected when I took that pic.
Since then I've removed the yellow speed control and jumpered the 'stat. It ran all night with no change in cooling.

[bcboomer]

So....after lots of diagnostic help from John at ColdEh Marine Refrigeration, it seems the system is plugged. Thank you John . Likely the receiver/drier is breaking down.
Unlike automotive systems, the receiver drier can't be easily replaced so I guess it's new fridge time
I'm really not looking forward to getting the old lines out and new ones in.
I'll probably go with John's recommendation for a NovaKool since his system is over kill for this old boat in BC.
Any and all tips to doing this will be appreciated.