NEFF G4344X6GB/04 freezer – intermittent alarm sounding

With apologies for the following soporific essay but I wanted to get all the evidence out in one go 🙂

The freezer is an under counter model in our kitchen at an ambient temp around 16C. It has an Embraco EMZ40CLC compressor and R600a refrigerant. When cycling normally the unit draws about 75W (mostly compressor of course) after settling down over a minute or so at the start of each cycle from an initial 100W or so. Compressor duty cycle is around 18 mins ON / 22 mins OFF. Each cycle starts normally with a mildly warm compressor producing a good hot discharge line, and mild frosting briefly on the suction line. By the end of a good cycle, the suction line has no remaining condensation, the compressor is comfortably warm and the discharge line around the door frame and back to the main condenser is warm. The main condenser is cold at the drier end and its cooling fan always runs perfectly whenever the compressor runs.

However, under fault conditions, the compressor cycle will start off at nearer 95W, falling after less than a minute to around 75W, but THEN drifts down to around 70W in the next few minutes from where it suddenly plummets over 5 – 10 seconds to a mere 45W draw where it remains for up to an hour or so whilst the freezer contents warm up and the alarm sounds.

Under the fault (45W draw) conditions the discharge line cools back to luke warm whilst the suction pipe warms to ambient. I have even opened the freezer, removed the contents and found the entire evaporator will warm up to ambient. Close examination shows the input current “flickering” a few percent up and down while at the same time I can just feel a frosty spot at the very start of the evaporator which will come and go as the power draw flickers. This condition can last for more than the hour I last had the patience to leave it before powering off. As soon as the unit is switched off, the refrigerant begins to start gently bubbling away somewhere, although I haven’t seen any corresponding cold/frost spots on the evaporator. Suddenly, after anything from 5 – 20 minutes, there will be an avalanche of bubbling, hissing and gurgling sounds and from that point onward, the unit can be powered up and will work for a while as if nothing had happened! To my untrained inexperienced eyes and ears it seems as though some contaminant in the R600a has frozen at the end of the capilliary in the evaporator!

When the compressor is turned off during this ‘fault’ condition and then turned back on within 1 – 15 minutes (before any gurgling noises have progressed), there is a good chance of stalling the compressor – my interpretation is that there’s no problem with the compressor OUTLET valve and pressure stays in the condenser side for some time. However, I can’t be so sure about the Suction (inlet) valve. Clearly when the compressor is only drawing 45W or so it isn’t doing much work and appears to be either scavenging a near vacuum, or the suction reed valve is leaking near 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d}. However, the suction valve theory doesn’t explain that after powering off, the circuit eventually “gurgles” it’s way through to an eventual cascading waterfall noise and the freezer recovers. )Unless of course someone tells me that weak inlet reed valves are common as ‘any fule kno…’)

Further observations:-
1. Provided that the thermostat is set low, the freezer won’t show any problems, but the contents will only be in the 17C – 19C range. If the thermostat is set to say 5 or 6 (out of 7) then with the contents at around -21 the freezer is bound to fail to the fault condition in a few cycles.
2. If the freezer is left in the low power ‘fault coondition for an hour or so with the door shut (but contents warming), eventually the ‘flickering’ power draw will suddenly start to drift upwards over a minute or so and resume normal 75W pumping operations, hot discharge line, normal freezing at the evaporator.

Has any of you refrigeration experts got any ideas or theories about what is happening here before I sling the thing and buy a new freezer on economic grounds? Or have I simply stumbled on an effect everyone knows about and then promptly turns the thermostat down a bit?! Thanks for your patience and thanks in advance for any suggestions… 😕