Cold fridges, however compressor runs almost constantly

[superheat6k]

That’s the way to often clear an ice blockage at the evaporator plate which restricts the gas flow, this can return quickly or stay ok for years.

Indeed, and indicative of prior poor practice where the pipework was not properly evacuated, leaving trace quantities of moisture which then accumulates and freezes in the throat of the capillary exit (coldest point on the system).

 

[Daverw]

Or due to the use of quick connect fittings which are already losing vacuum during storage

 

[driver0606]

What many fridge engineers do not know is that the BD compressors mentioned in the first post run at fairly low gas pressure. I think, maybe 0.5 bar. Check with Penguin refridgeration, UK. Along comes your average engineer. "Hmmm, not getting cold enough, needs more gas" he says, pumps it up and makes it no better, probably worse. You change engineers and it happens again. Been there, done that.

 

[Daverw]

Not sure you correct, the 0.5 bar is the suction pressure and any experienced refrigeration engineer will charge to the operating suction / saturated gas temp / superheat and not just add gas to see what happen. A compressor is a compressor and laws of physics are fixed.

 

[superheat6k]

What many fridge engineers do not know is that the BD compressors mentioned in the first post run at fairly low gas pressure. I think, maybe 0.5 bar. Check with Penguin refridgeration, UK. Along comes your average engineer. "Hmmm, not getting cold enough, needs more gas" he says, pumps it up and makes it no better, probably worse. You change engineers and it happens again. Been there, done that.

Your understanding of the compressor's basic function is incorrect. The suction pressure is a function of the evaporator and evaporating temperature, the compressor is just a pump drawing that refrigerant pressure. For a fridge operating at say 5oC the plate needs to operate at ~ -3 to -1oC, this equates for R134a to a Saturated Evaporating Pressure of ~ 1.6 to 1.8 bar. If the suction pressure is 0.5 bar then the Saturated Evaporating Temperature is ~ -17 oC, at which pressure the plate would be a solid block of ice - but only if refrigerant is boiling in the evaporator.

If the system is short of gas then yes the suction pressure will fall, but with no liquid refrigerant entering the evaporator there is no evaporation.