Hoping someone will be of help.
I am having 12v trouble with my Dometic fridge (240v and gas are fine). When I check the voltage (engine on) I am reading 12v on the fridge control (pins X104 and x103), however as soon as I switch the fridge to 12V this drops to 0.5v and stays at that voltage until I switch off the fridge andand restart the engine.
I suspect it is the Sargent EC155 supply unit EC51 control panel.
Has anybody else had this problem, and would it mean that I have to replace the units or is there a repair service that someone could recommend?
I have noticed that the EC51 control panel prior to this wasn't always switching off when the engine was running, and the vehicle battery select & level has never worked since I bought the van.
Thanks in advance
Your fridge controls should be wired from your leisure battery. As when switching engine off the voltage drops to .5 volts suggest your leisure Battery is shot. What does voltage on leisure Battery show when engine not running. If good and ully charged should read 12.6 volts.
Thanks for the reply. Perhaps I haven't explained the problem well enough.
There is no problem with the leisure battery, voltage is fine.
The fridge works as it should on 240v and gas but not on 12v.
The fridge does not work on 12v (engine is switched on). When I check the 12v reading with the multimeter, there is 12v reaching the fridge UNTIL I switch the fridge to 12v (engine is on). This voltage then drops to 0.5v.
I have had the Dometic fridge tested and there is no problem there.
Therefore I think it may be the actual Sargent EC155 control system.
you are aware i presume? that there is a relay that only allows power to the fridge over 1200 revs? anything below that and the relay shuts off power from the car to stop the battery in the car going flat/not starting
I cannot see how the Sargent EC155 has anything to do with this as only the control panel voltage passes through this,the voltage to operate the fridge element is direct from the Alternator via a voltage sensitive relay. As said modern Smart Alternators only cut in and charge when required. A previous motor I had to put my headlights on to get it to cut in then the fridge worked. Headlights could then be switch off. But each time engine switched off and then started again lights had to be put on again to start charging to operate fridge,
The Sargent controller will have control over the 12v supply to the fridge control panel supply so that it can be isolated when you 'turn off' (to everything!) the caravan 12v system.
The 12v supply to the fridge control panel (from leisure battery/charger) and 12v to the fridge heater cartridge from car towbar (ignition controlled - engine running only) are entirely separate, although it's normal to have a relay as part of the Sargent controller that detects when car supply connected and disables certain 12v caravan devices (to stop EMF (Electromagnetic Frequency nuisance signals messing with the car electrics). Quite what this relay actually controls/switches is often poorly documented and unclear, but MAY be part of your problem.
With poor connections/duff relay contacts, it's possible to get a 12v voltmeter reading off load, but as soon as a load goes on it can dive to a mere fraction of that due to high resistance!
Sargent have a technical help desk, may be worth a word with them about how the Controller handles various supplies.
My car has a Smart Alternator, but the caravan fridge works fine at tickover without any low voltage alarms or disfunction. The car battery voltage is just above 12V after engine has been running long enough to replace charge used to start the engine.
It's true to say the fridge will likely have a low voltage protection feature that will trigger an alarm and/or disable it if the car 12v supply is inadequate. That can come about through a combination of things, the tickover speed battery voltage is low, and/or any connections in the supply circuit are poor and causing a volt drop, around 11.6v seems to be the bottom limit.
So far all assumptions have been it's a fridge/caravan fault! Let's muddy the waters further!!!!
Huge variation here on what is actually fitted as part of any towbar wiring, but my towbar electrics (13pin) seem to have a 'trailer attached' sensing feature, whereby there is no output on the towbar socket pins when measured with a meter alone across live-earth pins, but plug in a trailer and all works well. Could it be the towbar electrics dropping the output when loaded?
Hi thanks for the information. The vehicle is a motorhome not a caravan so no towbar electrics.
I have sent Sargent a message, so hopefully they will be of help.
I will post any information here once I hear from them.
All help is much appreciated.
Received the following reply from sargent
the ec 155 needs the engine run signal to pull in a relay to power the fridge this should be checked , i have attached a basic diagram that may help, input pin 7 out at pin 1 , but the PSU could be faulty if no voltage.
The relay for an Autotrail Tribute T620 is beneath the passenger seat, next to 2 fuses. Ordered and fitted a new one and all is now working.
Diolch/thanks to everyone for your messages.
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Topic: 12v fridge and Sargent EC155
via mobile 08/6/2025 at 7:13am
