Webasto Isotherm fridge voltage issue

[Captain Phil]

Hi I have a Webasto isotherm fridge which has developed an issue.

The unit plugs in to the supply via. dometic voltage reducer/mains/dc switch affair

Having isolated he various inpt voltages it appears that the unit will run find on 240 and 24v (suppplied direct - not throught he dometic box)

But athough the dometic box is putting out 13.3v output the fridge will not start with that - or any other volt supply

The unti used ot run off the 12 v supply so not sure whee to look next - any ideas please

 

[Bodach na mara]

I am slightly surprised that you have had no response to the question but it is a rather technical issue, that requires access to the technical data and tables for the compressor and control unit. I found this information online after I had converted the ice box, built into the space behind the sink in a Westerly Renown, to a fridge. The evaporator plate was mounted in the box and the compressor unit mounted under the adjacent berth. The system worked, but it kept shutting down if the engine was not running. I had no shore power on that boat. My DC power was from a 24 volt battery bank, a common arrangement where the older Watermota diesel was installed as it needed 24 volts for the starter and was fitted with a 24 volt alternator. The problem stems from the rather clever voltage selection system within the control system. This attempts to select the best available system to supply its power. If an AC mains system is available it will use that provided that the voltage lies with certain limits. If not it looks for a DC supply and again there are limits. As supplied, it is well matched to a 12 volt supply. I don't have access to the tables but from memory it will cut out to protect the battery if the voltage falls below 10.8 volts and also cuts out if the voltage is too high, a figure of 14.3 volts is vaguely remembered. My problem is that with a 24 volt supply it cut out if the supply voltage fell below 23.5 but was happy with an over voltage of nearly 30 volts. A minor piece of circutry was required to connect a resistor into part of the thermostat circuit. I went further and constructed a small box which also incorporated warning lights which indicated when it was powered up, working normally, and a third light displayed a flashing fault code if it shut down. Unfortunately I have no idea where all the relevant diagrams and data are. I suspect that it is all on my desktop that failed years ago and is still sitting in the roof space at home. One thing that I can remember. The current drawn from the 24 volt system was over 2 amps, so your system is not drawing enough current. Maybe it is confused by the presence of a second DC volt somehow.