Danfoss bd50 Compressor, not cooling.

[Sailor L]

So our compressor got filled with new gas about half a year ago. I installed a new thermostat. Replaced it electric control unit. Everything should be working. As soon as i turn on the fridge. The compressor runs. Eventually gets warm. The fan is on. The coils are clean. I can hear the coolant/gas trickling. I even did a double check at the compressor if there is gas in it (there is). However the fridge is not getting cold.

The fridge has been off for 6 months. Getting all the new parts ect and deciding what to do.

The fridge is connected directly to the batteries. I measure 12.5v at the terminals of the control unit. The amp draw is minimal. It sounds however the compressor is running in a low rpm… any ideas? Could it be overcharged?

[Turtle Blues]

Possibly yes. Only way to answer your question is with a gauge on it. Quick search here should find Richard Kollman's extensive write up on that compressor and troubleshooting. He was the guru when I was a lad. Would love to find a copy of his book, long out of print.

[CarlF]

Yes. Badly overcharged could create these symptoms. Ger a tech with guages. Running it while overcharged can damage the compressor

[Bellinghamster]

Minimal amp draw, compressor running and warm and not cooling the fridge is most likely undercharged not overcharged. Gurgling sound indicates there is at least some refrigerant in the system. You said your system was charged with new refrigerant last year - did the old refrigerant leak out? If so, was the leak found and fixed? If not, that's the first step before attempting anything else.

You said you replaced the thermostat - did the fridge run properly after that? The thermostat usually includes a resistor in series that sets the compressor RPM. It may be possible you've got the wrong resistor causing the compressor to run too slowly for the application.

As an earlier post suggested, search here for posts from Richard Kollmann as he offered a lot of good advice for troubleshooting Danfoss compressor systems (he passed away recently). His website that included tech tips is not longer active, but fortunately an archive of it can be viewed using the Wayback Machine: https://web.archive.org/web/20181018.../techtips.aspx

[Bowdrie]

All those BD compressors, no matter the number/series, are extremely reliant on having just the right amount of refrigerant.
There must be zero leaks, the most common places of leakage are the male/female couplings and the place where the copper tubes enter/exit the aluminum evaporator.
A third place to carefully check for leaks are the Schrader valves,
The tech just can't just dump-in some refrigerant and use pressure readings to get an accurate measurement of charge.
The units need to be evacuated/vacuumed and the new charge put in by the specified weight-of-charge.

[barnab]

I would also vote for underfilled, if overfilled you would likely see a lot of frosting on the pipes to and from the compressor.



Compressor speed can be set with a resistor between (if I remember correctly, check the manual) C and T, the lowest and third contact from bottom. No resistor = lowest speed, so maybe your new thermostat is the problem. 1523Ohm should give you max RPM - again, check the manual for your exact model, it might be different.


But to be honest, if lowest RPM doesn't cool at all I think your refill just leaked out and you need to find and fix the leak. The best would be to evacuate as Bowdrie said, this allows you to also verify if there is a leak. Refill only makes sense if you fix the leak, unless you want to refill every couple of month.

[Bowdrie]

Originally Posted by barnab

Refill only makes sense if you fix the leak, unless you want to refill every couple of month.

You're right.
I would add that a leak on the low side is more insidious than one on the high side.
With a high side leak, you lose refrigerant, (you notice lack of efficiency and add some refrigerant,) but the ingress of non-condensable air is unlikely unless most of the entire refrigerant charge is exhausted, at which point a simple temp change between ambient and system will draw air into the system.
A low side leak is less detectable under operation as the pressure is lower on the low side.
What happens with a low side leak is that during the off cycles refrigerant leaks out, (the pressures between low side and high side equalize).
Then, when enough refrigerant has leaked out and the compressor re-starts, the low side goes into negative pressure and the suction of the compressor starts drawing in air thru the leak.
The air won't condense, and it drives-up the pressure/temp/power draw, and the compressor gets hot/overheats.
The compressors depend upon return refrigerant gas, (and the oil it contains,) to cool/lubricate the motor, (a portion of the initial oil charge is always circulating with the refrigerant).

[Colin Stone]

Agree. Uundercharged. When I added an un precharged filter dryer to my system, I had the same symptoms. Adding the missing 50 g of refrigerant and system performance restored.