Danfoss BD50 Compressor pulling way too many amps

[OzePete]

Originally Posted by Richard Kollmann

Pete, I still can not understand the refrigerant pressures you are recommending especially in tropical climates. I though maybe it was the difference in PSIG verses PSIA gauge sets. Are you aware that most water cooled Danfoss BD compressors have much shorter lives because if lack of cooling. The only compressor cooling on Matt’s compressor is provided by adequate flow of cool refrigerant returning from evaporator. For thirty five years fan air cooled systems have operated with high side pressures of 105 psi to 120 psi . The higher pressures you recommend increases the process heat to disposed of in compressor. As for as low side pressure running as high as 15 psi the results in box temperature would be no colder than a drink cooler. Capillary tube flow control devices are dependent on gas vapor volume and not liquid volume like an expansion valve. Fifteen Psi on low side is fine on low side in a system with a thermo expansion valve because it controls a much wider evaporator super heat than a fixed volume refrigerant Cap Tube System. Matt’s water cooled freezer unit with 134a refrigerant should also not be run below 4 psi to maintain some compressor cooling and while in tropical condition both compressor and control module need additional fan cooling.

Hi Richard,
Again I stand by my figures because they are correct and anyone out there who has observed the suction and discharge figures on a system operating in the tropics can confirm. Obviously in colder situations pressures are lower but lets look at the example we are working on. You stated that my figure of 140 PSI high side was wrong! Really? Surely you are aware that the high side is usually 6C to 8C warmer than the atmosphere (If it wasn't warmer the condenser simply would not condense refrigerant, agreed?) So if the air temperature is 37C add say 6C (assuming a very efficient condenser) and the high side will relate to approx at 43C or about 140 PSI as stated on R134a !
My figure of 2 to 15 PSI suction (depending if in the start, middle or nearing temperature cut out of a cycle) is absolutely correct and it is typical for the low side to be around 15PSI at the early portion of a cycle. Of course poorly engineered systems and differing environments will vary these finding and perhaps you are basing your findings on kinder conditions.
But I do agree with your comments regards air cooling the compressor and it's electronic driver. This is why our air / water cooled system has the fan also operate while running. Cheers! OzePete Ozefridge.com.au

[OzePete]

Originally Posted by ColdEh Marine

Also , you do not want to check for leaks using a vacuum . Using high pressure nitrogen is the preferred way . You can get the system up to 200psi or more and then hold the pressure there . Much better way . Moisture boiling off will give you a false reading and if you do have a leak all you are doing is sucking in air and just making more work for yourself. Also how are you going to find a sucking leak ...... use soapy water ?

Regards John

Good advice John, but I must say I shudder when I hear of anyone suggesting nitrogen. And just want to urge caution for anyone using it.

Back in the mid 1960's I was a young bloke being trained by Frigidaire in Dandenong Australia when word came in that one of our team wouldn't be joining us, he was dead. Blown to pieces by a 'pancake' type compressor that exploded like a hand grenade. He had connected a nitro bottle via copper to an old fridge. The regulator was faulty causing huge pressure and the explosion. If the old fridge had had a crappy aluminium evap instead of the steel tubing of those days, he would have survived.
Just want to mention that and urge that nitro bottle to system should be via a regulator and hose only not tubing!
Cheers. OzePete Ozefridge

[Typhoon]

Originally Posted by OzePete

Good advice John, but I must say I shudder when I hear of anyone suggesting nitrogen. And just want to urge caution for anyone using it.

Back in the mid 1960's I was a young bloke being trained by Frigidaire in Dandenong Australia when word came in that one of our team wouldn't be joining us, he was dead. Blown to pieces by a 'pancake' type compressor that exploded like a hand grenade. He had connected a nitro bottle via copper to an old fridge. The regulator was faulty causing huge pressure and the explosion. If the old fridge had had a crappy aluminium evap instead of the steel tubing of those days, he would have survived.
Just want to mention that and urge that nitro bottle to system should be via a regulator and hose only not tubing!
Cheers. OzePete Ozefridge

Yes yes , make sure you have a gauge that works and is set properly before opening the tank, bad things can happen.

We don't have to worry up here to much about this , you have to be a tradesman and have an account with the supplier to even get the stuff. But it is essential to do the "right job". We pressure test all our systems as Im sure you do to Pete.

This kind of work is best left for the professionals .

Regards John.

[Richard Kollmann]

Pete, The liquid and gas pressures I convey are those used by Adler Barbour for thirty years when refrigerant in the field could not be serviced correctly in 80 to 120 grams per weight. Having spent 25 years in tropical water conditions and advised at least 2,000 boaters of DIY refrigeration servicing I must continue to point out possible long range compressor damage operating with high refrigerant pressures. In South Florida there are over 300 miles of water ways filled with boats and many keep on board 12 volt refrigeration running all the time. Six months of the year the water temperature is 90 degrees F (33C).

PwrStkr, Mobile 12/24 volt refrigeration ice box conversion systems now use modern electronics circuits to control and protect Danfoss BD compressor armature rotation. The brains for this brushless motor are in a separate control module box containing protection circuits monitoring amperage compressor speed and voltage. During the compressor starting boot up should any design software limit be exceeded module will stop compressor and alert operator with a fault code. On these modern designed compressors you will not find, High Pressure or Low pressure switches, Lock Rotor thermo switches, or Hard start capacitors.

On these BD compressors high fan current amperage was intended to stop compressor in the event fan was not producing adequate air flow causing pressure and compressor temperature increases. Most manufacturers of water cooled systems using BD compressor fail to include this high temperature/ high pressure option that under the right conditions has caused complete system failure and replacement.

As far as leak testing with dry high pressure nitrogen regulations in my country require a 200 psi safety valve after pressure regulator.

The first place to check for refrigerant leaks on this type system is at servicing port cap seal and refrigerant line connectors. If air contamination is the concern each of these connections are exposed to vacuum pressure on each warm pump down start.

[Pyxis156]

Originally Posted by PwrStkr

The best thing to do is remove the refrigerant, fix leak and weigh the charge back in.

Originally Posted by OzePete

...any leak should be identified, repaired, have the filter dryer replaced then be evacuated before recharging.

Originally Posted by ColdEh Marine

This kind of work is best left for the professionals.

Respectfully, all good advice if you have access to the equipment to resolve this problem correctly or to the tradesmen that can do it for you. However, the OP is in a remote location without even gauges (at least for now). I am sure suggestions for how to try to get the freezer limping along long enough to get him back to Australia would be the most helpful at this point.

Matt, just an observation on system pressures I experienced charging my system after I fixed my leaks. The pressures I ended up with were in the ballpark of what Richard suggests are correct. If the high pressure side got much over about 120 PSIG for more than a couple minutes the system would start to lock up with the overload condition indicated. The low pressure side would drop to about 10 PSIG in the first 8 minutes of the compressor running and then as the evaporator begins to really start working, pressure drops to at or just over 0 PSIG (evaporator plate temps around -15F if I recall correctly).

[Typhoon]

Yes you are correct, sorry for the thread drift .

Regards John.

[Richard Kollmann]

Pyxis, Best thing you can do is forget every thing you read hear and face the problem as a boat master DIY professional. The only tools you will need to correctly service your refrigerator are an ammeter that will read amperage between 3 and 10 amps. And correct refrigerant with servicing adapter hose kit.

I gave a link earlier in this thread to my web site section on refrigerant charging.
1.The first step is to identify compressor BD model
2. With compressor running more than 10 minutes report amperage of unit and if air or water cooled.
3. Type and size of evaporator holding plate or thin aluminum plate.

With the above information I will be able to send step by step directions on adjusting refrigerant volume for best performance using the ammeter.
Email the information above and I will send you back what ever information you need to correct your problem.
Richard Kollmann

[PwrStkr]

Thanks, I had not thought of that, sometimes I miss the obvious and did not snap to being DC.

[teneicm]

So a quick update for all that were following this thread. First, big thanks to Pyxis , OzePete and Richard Kollman for their assistance both offline and in the thread. It looks like we managed to get the unit back up and functioning.


My initial thought was to uncouple the plate and take the compressor/condenser unit up to the local tuna canning plant where they would have the capability to vacuum the unit out. OzePete thoughtfully advised against this as a good portion of the (possibly contaminated) refrigerant would be left behind in the tubing and holding plate. Pete came up with the following plan to use the compressor itself to vacuum out the system:


1.Let all the gas out.
2.Connect your can of R134a ready to go.
3.Disconnect the discharge coupling only. (The one that goes on to feed the capillary)
4.Depress the coupling part that is on the compressor unit side so it remains open. (Perhaps push open the couplings valve and then put a piece of wire to allow it to slowly vent.)
5.Run the unit for 10 minutes. Gas etc should exit the partly opened coupling.
6.Leave running and then slowly allow some R134a into the system (About a quarter of your can)
7.Leave running for say another 5 mins as this is discharging.
8.While still running, reconnect the coupling back to normal
9.While still running slowly add R134a gas. Watch your amp meter and only charge to about a run consumption rate of 6 amps.
10.Leave running for several hours and observe specially the suction pipe. Ideally the suction should be cool and the liquid line just a bit warmer than body temp. (Check by feel at the couplings)


This process worked well and the unit now seems to be operating fairly normally. Once the box got down to temperature, the unit was only drawing about 4-5 amps at a 'normal' run speed, so it may be that I'm still a bit light on the refrigerant, and I may add just a bit more. Especially since it seems like it is not cooling quite as rapidly as it did before (previously would drop the temp about 3 degrees in about 90 minutes, seems now it takes about 4 hours to do the same). But either way, we're over the major hump and now down to tweaking for performance!