First Find problem with non destructive means

[Richard Kollmann]

This came as E Mail, but I am posting it here in hopes it will remind others that non destructive action alway comes before tampering with refrigerant.

Problems with Freezer

Hi Richard,
we are having a problem with our 12v Danfoss BDF 35 freezer, would appreciate if you could help with some info.

The freezer seems temperamental, works for weeks/months then stops to cool. I fiddle around a bit and it starts to work again for a while, at present the symtoms are as follows:
compressor running, a bit louder then before, gets very hot, on some occasions the led ind light was flashing 3 times, not cooling, no icing of tubes, evaporator only sweating, no gurgling noise

I have played around with releasing and adding refridgerant, and am in possession of your instruction how to establish if the system is under/overcharged. But am still not sure what the state is. At one stage I refilled gas, noticed the motor slowing down then stoped, sounded like too much gas and I overloaded the motor, 5 LED flashes.
Can I start from scratch, release all refrigerant and start re gassing?
Thermostate, is that a n/c contact til the set temp is arrived at or the other way around?
BTW, I do have a new compressor as a spare, would you recommend that I connect it and see if there is a diff or would that be a task for an exp refridgeration mechanic?
How should the compressor speed RPM potentiometer be set?
Would be gratful for any tips and info,

ANSWER:

When one of these Danfoss BD compressor refrigeration systems has been running well and then stops running it has nothing to do with refrigerant level. Tampering with refrigerant is the same as shooting yourself in the foot as it takes time and money to correct what was done. If in the beginning there was a three flash LED signal and no one had tampered with refrigerant system, this overload was caused by poor condenser cooling. If there was a single LED flash your problem was in the boats electrical system. If again,in the beginning there was a two LED flash the fan needs to be replaced. You may have contaminated the refrigerant and oil with air and moisture at this point, if so the system will require an extensive dehydration and filter replacement.

I am assuming that no one has added a resistor to the thermostat wiring. I am also assuming you have a standard aluminum evaporator. The normal refrigerant volume is indicated by frost coverage on evaporator. One hundred percent of evaporator covered with thin layer and no frost on line outside box is the correct refrigerant charge.

At this time I would recommend removing small amounts of refrigerant at a time until compressor will run continuously.
Compressor must be off for several minutes before removing refrigerant each time.
Removing refrigerant for 2 to 3 seconds each time is sufficient.
Once compressor runs OK wait 30 minutes and check evaporator frost coverage if there is less than 95% frost coverage too much refrigerant was removed.

[gbanker]

Totally agree with Richard. I had a "technician" add refrigerant to my system only to find after he left that there was frost on the return line all the way back to the compressor. Removing refrigerant, waiting, and checking frost until the frost line was back to the plate fixed my problem.