Dometic CS-NC-15 cooling unit help needed

[sharkwatcher]

I need help, I have a Dometic CS-NC-15 fridge unit that was installed by the previous owner that is not functioning properly. For those that are not fimiliar with this unit, if is a "Drop in" DIY unit. It uses a Danfoss BD35F compressor and control module.

The problem is: It starts and runs for about a minute or two, shuts down and the tries to restart again after a minute or so. It continues doing this while quickly running the batteries down. Both the fan and compressor starts and runs each time.

My house battery bank system consist of 6 6V batteries, each pair wired in series, then wired to the other pairs in parallel. total voltage is ~12.6 V and 660Ah.

Any help or advice would be greatly apperciated. Thanks!

[GordMay]

Service Notes - Danfoss BD35F ➥ https://www.isotherm-parts.com/PDF/s...leshooting.pdf

See also ➥ Kollmann Marine

[sharkwatcher]

Thanks GordMay

[Richard Kollmann]

My first question is there a $3 troubleshooting LED installed on your BD35 compressor? If LED flashes a code how many times does it flash every four seconds?

Has anyone tampered with refrigerant or connected gauges to this unit?

How do you know the compressor is actually running is it getting warm after running 20 minutes?

How long does it take to drop battery bank voltage to 12.5 volts?

The actual time compressor runs before shutting down can help pinpoint trouble 60 to120 seconds can indicate Danfoss control module has a problem maintaining steady three phases to compressor field coils. If compressor stops in less than 30 seconds there is a low voltage spike in boats wiring or the fan is drawing too much current. One to two minutes running time could mean a poor ground in wire from battery ground to Danfoss module's large minus terminal.

Standard tests without trouble LED codes on Danfoss BD compressors

1. Place jumper wire across thermostat terminals, Compressor still does not run.

2. Disconnect black fan wire from electronic module, Compressor runs replace fan. Compressor still does not run after fan ground wire is disconnected. If one of the 10 transistors in this fan fail it can cause module to prevent compressor from running.

3. Run correct size and correct polarity fused jumper wires direct from a fully charged battery to module in order to bypass all boat’s wiring. Volt meter readings are of no value, Compressor still does not run electronic module needs to be tested on another unit.

[sharkwatcher]

Firstly, there was no LED installed, but after reading other threads by you and others about the BD35 unit, I installed the LED myself, between small+ and D terminals. I'm not getting a code. the compressor is diffinitely running, it is warm after running 20 minutes with the T and C terminals jumped. The circulating fan is not running, but the coil is freezing up. With the thermostat hooked up, the unit runs 2 minutes before shutting down, down for a minute the restarts. I have not tested to see how long it takes for the battery voltage to drop. I suspect the circulating fan my be part if not most of my problems, but have not replaced it yet.

[sharkwatcher]

BTW, the compressor has to the best of my knowledge not been tampered with or any guages hooked up to it.

[Richard Kollmann]

There are two fans on that unit both will be running when thermostat is running compressor. This means the Small + and F terminals that are designed to detect excessive fan amperage problems greater than .5 amps (500 milliamps) would normally stop compressor from running. In your case I think it is not high fan amps but high system amps.

Based on your report I would suspect the 4 inch fan on top of compressor is not drawing any current and condenser is overheating causing module to stop compressor. To confirm that unit is stopping due to high temp, high pressure amps place any fan in the area to move air around condenser coil. If this test extends compressor running time as long as air is moving around coil try another 12 volt fan. I have done this test by moving air in this area with a piece of cardboard.

[sharkwatcher]

Thanks Richard, I'll give this a try.

[sharkwatcher]

With the thermostat hooked up and using my wifes blow dryer as an aux fan, the unit ran continously for 20 minutes, until I shut it down. I ordered a new fan! Thanks everyone!