Locked Rotor BD50 Refrigeration Compressor

[RaymondR]

I just put a condensing unit which has been out of service for a couple of years back into service. The fan starts but the compressor does not. The LED flashes 3 rimes which according to Danfoss indicates "Locked Rotor".

Any suggestions which might lead to a solution would be appreciated.

[GordMay]

According to Richard Kollmann:

Originally Posted by kollmann-marine

Three LED flashes indicate excessive torque is required to start compressor. This is commonly caused by turning compressor off and back on too quickly or too much refrigerant or poor condenser cooling. Most people jump to the conclusion that there is a mechanical rotor lock up inside compressor and this is a mistake on Danfoss BD compressors.

If someone has tampered with refrigerant by connecting gauges to a system letting air in or adding too much refrigerant can cause either a Three or Four LED flashing signal. On water cooled Danfoss condenser systems three and four LED signals are common when seawater gets into refrigerant circuit.

See also:
Checking Locked Rotor
➥ https://www.shearersupply.com/ASSETS...otor_rev.1.pdf

Originally Posted by Richard Kollmann

There are two different series of Danfoss BD 12 volt compressors the older fixed speed and the newer variable speed . If the refrigeration unit is over 10 years old and has a Danfoss BD 2 or BD2.5 or BD3 compressor then it has the older fixed speed discontinued electronic 4 pin module. Troubleshooting Danfoss compressors with 4 pin modules consists of the following steps:

1. All of these compressors have a 4 pin module connector and their modules contain a replaceable fuse. If this fuse is blown there are two reasons why either power wires to module are reversed or module has an internal failure.

2. Check to see that there is actually power at the refrigerator control module.

3. Place jumper wire across thermostat terminals on electronic module, Compressor still does not run go to next step.

4. Disconnect black fan wire from electronic module, Compressor runs, replace fan. Compressor still does not run after fan ground wire is disconnected, go to next step.

5. Run correct size and correct polarity jumper wires direct from a fully charged battery in order to bypass all boat’s wiring. Volt meter readings are of no value when looking for voltage spikes. Compressor still does not run electronic module needs to be removed and tested on another unit. If there are no other units available to test your module on I will test all 12 volt Danfoss control modules free except for BD80 compressor modules. Email me for shipping address and details. richard@kollmann-marine.com

Small 12/24 volt boat refrigeration units using Danfoss BD compressors manufactured after 1996 will have a BD 35 or BD 50 variable speed compressor with a troubleshooting computer chip built into control module. This circuit makes them easier to find troubled area if compressor fails to run. If this unit does not have this $2 LED install one. Without the LED on these new units troubleshooting will be the same as earlier 4 pin Danfoss BD compressors.

Trouble shooting LED will only flash if electronic module sees a compressor problem. In each case problems of compressor’s failures to run are identified by counting number of flashes of LED:
• No LED flashes would indicate either thermostat is open or no power to module.
• One LED flash and a 4 second pause indicates a non Danfoss wiring electrical resistance problem or low batteries. Because of module’s sensitiveity to milliseconds of a voltage spike they cannot be detected by a voltmeter. Solution is to bypass power wiring till resistance problem is located.
• Two LED flashes indicates fan over current cutout. If fan circuit on these variable speed compressors exceeds ½ amp compressor start up will be aborted. This condition can be confirmed by disconnecting Black fan wire at module, if compressor runs replace fan.
• Three LED flashes indicate excessive torque is required to start compressor. This is commonly caused by turning compressor off and back on too quickly or too much refrigerant or poor condenser cooling. Most people jump to the conclusion that there is a mechanical rotor lock up inside compressor and this is a mistake on Danfoss BD compressors.
• Four LED flashes indicate compressor motor not reaching sustained controlling speed above 1,850 rpm quick enough.

If someone has tampered with refrigerant by connecting gauges to a system letting air in or adding too much refrigerant can cause either a Three or Four LED flashing signal. On water cooled Danfoss condenser systems three and four LED signals are common when seawater gets into refrigerant circuit.

Originally Posted by Richard

1. the troubleshooting LED will only flash a code signal when there is an electrical problem preventing compressor from running.
2. The evaporator temperatures in box will indicate how well the unit is running and if refrigerant volume is correct..
3. the thermostat turns compressor off and on, if kept running box temperature will keep dropping.
4. the amperage draw tells how much work is being done at that point in time. When your BD 35 compressor is first started it will reach 5 amps of current draw in 10 minutes. If after 10 minutes compressor is performing at less than 5 amps compressor speed is set too low or refrigerant volume is less than correct or speed is set too low. Compressor speed setting can be determined by milli amps of current flow in thermostat wire loop, See Danfoss compressor data sheet

Richard has contributed a great deal of refrigeration knowledge, to CF:
More posts ➥ https://www.cruisersforum.com/forums...rchid=36464872

Unfortunately ➥ https://www.cruisersforum.com/forums...ml#post3779852

[RaymondR]

Pretty sure I did not get any air into the system and vacuumed it down and closed it in for about 14 hours to check it was holding vacuum then vacuumed the system down for a further couple of hours so fairly sure it did not have any air in it then charged it up.

It's cold here and the refrigerant is only holding about 50 psi but it's the same on both high and low sides so the compressor is not attempting to start up against a large differential.

[Tin Tin]

What refrigerant are you using, depending where you are the proper stuff is hard to get hold of.

[RaymondR]

Originally Posted by Tin Tin

What refrigerant are you using, depending where you are the proper stuff is hard to get hold of.

It's a hydrocarbon based one supposed to be compatible with both types of oil.

The hydrocarbon based refrigerant I use is sold at auto shops in Australia as an auto aircon refrigerant. It is also widely used in Europe for domestic refrigeration.

[pjShap]

SeaFrost recently sent me a troubleshooting guide, hopefully attached to this post as a PDF. The guide says when the fan runs, compressor does not run, and 3 flashes the problem can be:
1. Overcharged- too much refrigerant.
2. Faulty electronics module.
3. Inadequate wiring. poor contacts, etc., so too much voltage drop.

[pjShap]

I forgot to add in the previous post the documentation for my unit specifies only pure R134A without any oil, anti-leak, or other additives. Most automotive refrigerant sold here in the USA includes oil and/or stop-leak additives.

[RaymondR]

Thanks pj,

Removing some refrigerant is my next move.

The unit has a small electronic panel in addition to the Danfoss power supply on the compressor and as a result the spade terminal count is double what just connecting to the compressor provides so rewiring direct to the compressor is my second move.

The non R134 refrigerant I use is primarily produced for the European market and has no oil or other additives. The reason one can buy it in auto parts shops is that it does not require and licenses or permits unlike R134.

[RaymondR]

I have tried bumping the compressor case fairly hard to jolt the compressor and bleeding off some gas via the high side service connection, also rewired around the small add-on board direct to the compressor all to no avail.

I think there are two more things I could try: The first to heat up the case, and consequently the oil, with a paint gun. The second to put the vacuum pump on the high side in an attempt to suck out any liquid from the compressor cylinder.

Overall I think it's probably time to replace the compressor since even if I could get it restarted I have no confidence it will be reliable.

[DeBe]

Had same problem with one of my fridges. It would give locked rotor code. I checked the resistances betwean each winding & they were close to correct but obviously not close enough. I cut the compressor open & found the center of the star windings had a spring clip conecting the 3 wires to gether. I removed the clip & refited it, hey presto the compressor would now run. I now use the dismantled compressor as a test unit for the controlers.

[DeBe]

Had same problem with one of my fridges. It would give locked rotor code. I checked the resistances betwean each winding & they were close to correct but obviously not close enough. I cut the compressor open & found the center of the star windings had a spring clip conecting the 3 wires to gether. I removed the clip & refited it, hey presto the compressor would now run. I now use the dismantled compressor as a test unit for the controlers.