12 volt fridge problem

[Norman_E]

It was working fine yesterday. As usual I turned it off for the night because its a bit noisy. This morning I turned it back on and its dead. Controller is a Danfoss 102N330 and compressor is a Sidmar unit with an otherwise illegible label. Whilst I suspect that the controller has failed I am also suspicious of the thermostat as the fridge had been operating on a very short cycle of about five minutes on and five minutes off. I did try short circuiting the thermostat connections on the controller to see if the compressor would start, and it did not. Am I right in thinking that if the thermostat had failed "open circuit" shorting the terminals for it on the controller would start the compressor? The controller has failed before and I had to re-solder some connections in it, but it looks OK inside this time. My multimeter shows that it has 12.8 volts at the input terminals so the external wiring is OK.

 

[roaringgirl]

What does the controller do? If it is possible to bypass the controller, does the compressor run?

 

[Norman_E]

Its a bit complicated as there are four wires from controller to compressor and two more to the fan. If the compressor was just a motor driven pump it would be simple enough to fix up a contactor relay to energise the compressor and fan when the thermostat demanded cooling. I have done that using a pair of contactors for my boats water cooled mains driven fridge compressor, with one controlling the mains circuit and the other one running the 12 volt water pump.

 

[roaringgirl]

What on earth else can the controller be doing? Maybe the 2 extra wires tell the controller if the compressor is overheating? How complicated can it be?!

 

[roaringgirl]

I don't think you need the 'controller' at all.

https://www.youtube.com/watch?v=kchIRqBopzU

you could try shorting the C&T terminals and giving the top 2 12v to see if the compressor runs.

From memory (I'm in Edinburgh, the boat is in Spain), we don't have a 'controller' and the wiring is all straight into the box mounted on the compressor.

 

[Hoolie]

I think you should make sure the compressor motor is 12v before trying this. I believe our previous Danfoss compressor was ac and the controller included an inverter. Don't know what its replacement is.

These controllers usually have an LED status output but you need to connect your own LED. It flashes in different ways to indicate any error conditions.

 

[Norman_E]

I don't think you need the 'controller' at all.

https://www.youtube.com/watch?v=kchIRqBopzU

you could try shorting the C&T terminals and giving the top 2 12v to see if the compressor runs.

From memory (I'm in Edinburgh, the boat is in Spain), we don't have a 'controller' and the wiring is all straight into the box mounted on the compressor.

On a Danfoss compressor that box is the controller and its just an updated version of the one I have. Mine is separate because the compressor is a different make.
This is the recommended replacement if my controller is dead. http://www.penguinfrigo.co.uk/shop/...v-dc4-pinfor-danfoss-bd3-earlier-compressors/

 

[Norman_E]

What on earth else can the controller be doing? Maybe the 2 extra wires tell the controller if the compressor is overheating? How complicated can it be?!

No, it is much more complex. The motor driving the compressor is brushless and has a fixed speed of 2500rpm with the controller evidently providing sequential pulses of current to start and run the motor which presumably has three stator coils energised in turn. That would explain the four wires as three positives and a common negative.