12/120 refrigerator

[Loyd Dinneen]

I just got a 1977 280 sda and it has a refrigerator/freezer in it and I believe it is a 12/120 unit and I'm not sure how it works or even how it turns on or switches to 12 volts and back to 120 volts. I have no way to hook it to a shorepower outlet as it is on a trailer. I'm really not sure if it even works at all can anyone out there give me some ideas on its operation. Thanks

 

[gerryb]

Its based on a power supply that is smart enough to sense the 120 circuit and use that power-in before it uses the 12v supply. The switching relay inside the power supply will go to 12v once it detects the lack of any 120 input. Best way to check what it is doing is to turn it on. The thermostat inside the unit acts as an on-off switch. If you don't hear a fan and compressor kick-on, then time to get to the back of the unit and check if there is 12v and 120v power back there. If no, then track it back to the breaker boxes and see if the breakers are on and power is going through them. If the unit is connected to a 12v and 120v supply, then I would suspect the power supply is faulty and needs to be replaced. Note the model number and look for a replacement, although with a fridge unit that old, I might just replace the whole thing as many other things could be wrong with it.

 

[Handsome Transom]

Just made a new thermostat and switch circuit for my 30byr old norcold works great took ten min and no money hecayse i had a salvaged rheostat and switch in my electronics box

 

[bobeast]

It's really just a relay. 120V opens a pair of normally closed contacts through which 12v is connected. When the relay is energized by AC, the contacts open and DC is removed. When you unplug, the relay de-energizes allowing DC to to be applied.

So if you hook your fridge up to a battery and have the temp setting at its lowest setting, you should be able to hear the hum of the compressor.

 

[Handsome Transom]

These fridges are actually DC ONLY when on shore power a Transformer supplies the DC current . A relay is the switch that decides which power source by sencing a higher amperage current from the DC transformer and then switches it from battery to transformer supplied current . If the power supply board is shot you can use Battery power only just eliminate the switching circuit your boats converter / charger will keep the batteries up.

 

[Handsome Transom]

Just made a new thermostat and switch circuit for my 30byr old norcold works great took ten min and no money hecayse i had a salvaged rheostat and switch in my electronics boxView attachment 55827 View attachment 55827

Oops left it set too high through the week and froze the milk great old fridge