Diagnosing 3-Way RV Fridge: 120V Cooling Failure, Thermostat Coil Issues

[MG Carter]

Domestic small refrigerator not cooling on 120v shore power. Cools on propane and sorta on 12v. Any ideas?

 

[bikendan]

Domestic small refrigerator not cooling on 120v shore power. Cools on propane and sorta on 12v. Any ideas?

It always helps if you posted what model number your 3-way fridge is since different model numbers are installed in FR popups and A-frames.

 

[MG Carter]

My Dometic is a 3-way and I have tested the 120v plug at the A/c and it’s receiving 120v. Is there an additional internal breaker I’m can’t see? Thx

 

[Brandoni]

MG
Is the tower (above the propane flame's location) getting hot when using the 120V??
If yes then increase the cooling number on the 120V dial.
If no then there is one of two things. First is the 120V heat rod isn't generating heat any more (burnt out) Check the resistance, it should be above 0 ohm (thinking about 100'ish ohms, 110V / 1.1 amps estimate). Second is a wire disconnected between the 120V input and heating rod.
Good luck with finding a working solution!!

 

[MG Carter]

No, the exhaust tower is not getting warn or hot. I’ll take your suggestion and follow the electric line from the plug. The first stop is the switch.

The heating tower does get a little hot with 12v. Does the same heating rod receive charge from the 120v and 12v switches? If so, it might be the actually manual switch?? I’ll check the resistance on the heat rod as well.

 

[tomkatb]

Depending on age. The resistance heaters do not last forever.

 

[MG Carter]

Thank you. 2018 so probably 6-7 yrs old but don’t know actual usage. How do I access the heater? Remove the tower?

 

[tomkatb]

First try some troubleshooting with a voltmeter.

Loose wires. Boards etc. are also common.

Lots of utube and other guides.

 

[Brandoni]

Thinking just now . . . Check the heat sensor inside the refrigerator . . . Make sure it's clamped in there correctly . . .

 

[tomkatb]

I think they all have a thermistor. These fail as well.

 

[Larry-NC]

One more thing: On ours, at least, if you remove the outside access panel, you will see two old-style cylindrical glass fuses. One is for 12 volts. The other is for the 120 volt circuitry.

Inspect the 120 volt fuse or remove it and test with an ohmmeter. If it's bad, get a replacement at an auto parts store.

 

[MG Carter]

Thanks everyone. Great advice!

 

[Brandoni]

Please let is know what your solution was . . . Or if more thinking cap is needed . . .

 

[MG Carter]

I checked 120v coming into switch and it was good. I disconnected the wires going to the resistance heaters with Omh meter and showed 88 so either the switch 120v switch is bad or possibly I need a new resistance heater. These small cubes are simple devices. No boards or inside thermostats. The 120v/12v switches are one piece. So that’s the direction I'm heading. Thanks

 

[MG Carter]

Help…now it’s over my head. The thermostat coil broke. Can this be repaired by accessing the box where the coil comes out under the switches or should I order another thermostat kit and reinstall it. That would require going in through the back wall and I have no clue what’s there. Thanks.

 

[Brandoni]

Looks like a new coil will be needed . . . Likely the tube passes thru a port hole from the outside to the interior of the fridge . . . The hole gets sealed/plugged (silicone or sealant) to keep the two sides separate. Coil is always bent with something (broomstick sized) round, don't attempt freehand curves.
There may be a part number on the coil box that will allow sourcing a replacement locally.

 

[MG Carter]

Thank you. Any ideas on how the coil leads attach to the inside coils behind the wall or do the just touch it.

 

[Brandoni]

definitely NOT knowing . . .
I'd expect the coil to travel thru the wall and have the sensing element inside the frig.
The sensing element sends pressure back to the coil box . . Which then controls the electricity thru a switch.
Dis-assembling the coil box to expose the inside workings may reveal some neat technology . . . ; ) (it's broken anyways . . . : )

 

[pgandw]

I have a copy of the DM 4223 installation/operating instructions. PM me, and I'll email the .pdf.

I don't recall nor do the instructions show any inside thermostat. In the Dometic install photos in the instructions I just see that coil sitting there that you called the AC thermostat.

What I do recall is the factory installation came nowhere close to meeting Dometic specs. And the counter above the fridge got very warm, almost hot, when fridge was running.

So I insulated around the fridge, added some Reflectix in the top of the outside fridge compartment, rearranged the gas exhaust, and anything I could do to improve air flow. All helped, but didn't get me over the hump in 90 deg temps, thanks to those "couldn't pass gas in a hurricane" plastic vents.

What did make the fridge reliable in all modes was installing a 12V computer case fan to shove warm/hot air out the top vent. This was detailed 7-8 years ago in a thread in the A-frame section entitled something like "Liking my A-frame fridge" started by me (pgandw). The same computer fan on the exhaust vent has worked wonders on the larger fridge in the HW A-frames (I used 2 case fans on the larger fridge).

Fred W
now 2019 Flagstaff T21TBHW A-frame
then 2014 Rockwood A122 A-frame

 

[tomkatb]

In the past I read specs for a living.

Most rv installations do not meet refrigerator specs.

We have the top rv guy work on our unit. He is a major fan of adding fans to the system. The factory installed two little computer fans. He installed a much larger squirrel cage fan. Our fridge works swell. Three fans.

Ours is a 13 cu. Ft. Unit.