1986 Saturn 1550 in South Carolina - Newbie

[1960Zimmer]

First camper I have owned. Need to learn a lot. Camper is all original, even original spare tire. Dometic refrig doesn't seem to work. Any pointers for this old of a model? I have it switched to electric and the thermostat to cool, but I have an open circuit when I check the plug's terminal with a Ohm meter (when unpluged and switched on. (yes the outlet is live that i tried it on)

[JohnB]

Hi and Welcome! Congrats on your new Sunny! The fun begins.

On the fridge, look for a model number, it would be inside the fridge compartment on one side of the fridge.

And, any pics of the outside behind the vent grate to show the back of the fridge helps too. I'm not sure exactly which older one you have. If it is still the original fridge, the thermostat could be the type that had a switch on it that just turned on and off the electric element.

Since you are new to the camper scene, these RV fridges work by creating heat in the boiler tube area. The gas in the cooling coil gets heated by LP gas flame or an electric calrod type heating element. There is no compressor with Freon. The cooling coil removes the heat from inside the fridge, leaving only cold left. I know that sounds odd, but that is the way these absorption fridges work, they remove heat.

If you can feel the boiler stack, above the gas burner getting warm after about 20 to 30 minutes, then the electric element is starting to do something. It can many hours, 3 to 4 hrs sometimes more to cool the fridge down and it is hard to feel it cold as there is no fan inside. You almost need a thermometer inside to know it is cooling down from ambient temp. The freezer section will feel colder if you touch the metal plates in the back.

The resistance of the electric element is low. This is where we need the model number to help better. Some of the older fridges ranged from 44 ohms all the way to a whopping 92 ohms across the electric element.

If you have a totally open circuit, (infinite resistance) OL on the digital meter at the 120 VAC cord plug hanging out of the receptacle, then check just the element by itself. Find the 2 wires to the element that is over by the gas burner. If the element itself is open circuit, then the element may be burned out. But if the element has some low resistance, the switch (part of the T stat) to turn the element on may be not making which is why the cord plug would show open circuit as the switch is not putting the element in the circuit.

Again, we need the model number to help better. I am guessing which older fridge you have.

Hope this helps

John

[1960Zimmer]

John,
The Dometic refrigerator is model RM2300. Some pictures are attached of the control panel and from the outside. The circuit is completely open even though the controls are set to electric and the thermostat is turned part way. Thanks for the advice.

[JohnB]

Hi,

I could not find a service manual for your exact RM2300, but I found some that are close.

See this link in our files section. The RM2300 is called out in this manual but it is not specific to just that model. And the pics are not the greatest but it can help https://www.sunlineclub.com/forums/d...do=file&id=417

Here is another go-to place I have found for some manuals on the Bryant RV site. https://bryantrv.com/docs.html I did not find the older RM 2300 in there either unless I missed it. The service manuals always cover more than just one model.

We had a U tube shown in a post not long ago of someone taking his gas valve apart on your vintage fridge. I'll hunt some more later to see if can find that and ideally a wiring diagram for you. In his case, the gas valve needed to be replaced.

But, you can back into your wiring as it is not that complex.

In your pic, on the left, there is a BX armored cable-looking wire coming out of the burner stack.


That BX cable has 2 wires going to the electric element heater that slides into a sleeve of the boiler assembly. The BX cable goes down into the top of the white box cover of the gas valve assembly. Start by taking the cover off the gas valve and look for the 2 wires coming out of the BX cable by the gas valve area. Unhook one wire and then test across the 2 wires for ohms across the element. If the element comes up as an open circuit, the element is toast/burnt open. A RM 2310, has 92 ohms +/- 10%. But, yours is a RM 2300 so slightly different. But this is a start.

If you find that the electric element has 90 some ohms, then this points to the T stat switch OR the main selector switch (it is controlled by a long rod from the front and changes from gas mode to electric mode) not passing the 120 VAC power to the element. Keep tracing with your ohm meter backward to the incoming 120 VAC power cord. This is a simple circuit, with only the big selector switch, the T stat, and then the element. You just need to find which is not passing the power.

Come back with more questions and pics if you need help. And please let us know how you make out. This helps the next person coming behind you.

Hope this helps

John

[1960Zimmer]

John,
Thanks for advice, I will follow your instructions. Can you tell me how the refrig's thermostat works? Is there a sensing bulb in the fridge or outside that controls a pressure switch that interrupts the electric circuit as well as gas? If so is there a pilot light (flame) that stays on all the time? Keith

[JohnB]

Hi Keith,

I found the post I was hunting for with the U tube about the guy changing out the thermoset. That video I do believe will be close to yours, just that RM 2500 has other gas ignition features yours does not. Yours I believe has the Piezo manual pilot lighting system when in gas mode.

This post has several links it, including an owners manual for the RM2300 that Thomascine uploaded out of her camper. The RM2300, R2400,RM 2500, RM 2600 & RM2800 all used the same owners manual. And this manual has an exploded view of the RM2300. Keep in mind which model you have and use the instructions that go with that model. A RM2300 "style" wiring diagram does show up on page 15 of the service manual, it is called out as "Typical 2 way with Piezo lighter" with bottom mount controls.

Your fridge would not have the 12 VDC electric element option. But it does have the 120 VAC electric element option. The 2 way fridge means, gas, and 120 VAC. The 3 way fridge is gas, 120 VAC & 12 VDC.


https://www.sunlineclub.com/forums/f...tml#post157544

And in that post is there is a link to the service manual that I think I already linked to you, page 15 is the wiring diagram as simple as it is.

These older fridges where mostly mechanical with limited electrical controls. The T stat sort of ran the show. It has a capillary tube with the bulb on the end that goes in the fridge compartment. The tube runs out to the T stat gas valve itself to receive the temp signal the old way through a capillary tube setup.

There are links in that post to a new T stat that shows what comes on the T stat itself. There are spade terminals on the side to run the element. The T stat gas valve and the contacts in it work both at the same time. While both the contacts and the T stat valve may open at the same time, this is where the big selector switch and an on/off gas valve before the T stat comes into play.

Your knob in the front of the fridge that selects gas or electric has a long rod that runs from the inside to the selector switch in the back of the fridge and it has a rod to the on/off gas valve. So when you are in electric mode, the gas valve is off, no gas is then sent to the T stat even if the T stat is open calling for heat. But the electric supply then passes to the contacts on the T stat. When the T stat mechanically calls for heat, and since the electric is selected, the heating element is energized.

In gas mode, the selector switch shuts the element power down, and opens the LP gas on/off valve sending gas to the T stat. The long rod turns both the electric selector switch and the gas valve. There is a gas pilot mode and a main burner run mode I believe in the T stat. While the contacts do turn on and off in gas mode, there is no power supplied to the element so the switching does not do anything.

Have a read up on those 2 manuals in the link and see if that helps. We are here to help with what may not be in the manual.

I have not worked personally on one of these old units. I have done a fair amount of work on the newer electronic PC board fridges. The cooling coil principle of the fridge is the same as it always has been, but the controls have changed along the way. We do have a a few others here who may have worked on the older units, so fee free to ask what you can't find or understand on your unit from the manuals.

Hope this helps, and let us know how it goes.

John

[JohnB]

Since this is new to you, and in case you did not know,

The RV fridge needs to be level when it is operating and the camper is stationary. Do not run the fridge with the camper off level. The fluid in the cooling coil does not flow correctly when the fridge is off level and can burn from overheating. And the damage from burnt fluid is not reversible other then have the cooling coil rebuilt.

Dometic did upgrade the cooling coil over the years to be more tolerant to off level, not sure what year that was, but even the newer Sunlines still need to be level. Your older one more then likely is the more fussy about being level type. Again, just level the camper front to back and left to right and it should be OK. You can put a small level on the fridge itself if wanted to make sure. Some times the camper main frames get bowed so knowing what level really is, is a question. The fridge itself is what needs to be level.

Hope this helps

John

[1960Zimmer]

John,
Thanks for all the info. I will keep you posted. Had to move the camper and will restart with leveling before getting into this. Thanks again

[mainah]

Just out of curiosity how long did you let it try to cool? They are nothing like a house fridge I usually turn mine the night before I go camping. There should be a small little window on the right hand side of the control panel if the flame is lit you should see a blue glow from the flame. It uses very little propane so turning it on a day ahead of time is not an issue. Level is good but don't stress over it generally if you are comfortable the fridge should be too.