Dometic RM56E freezes

[RichB]

My 1978 Land Yacht has a Dometic RM56E Refrigerator. It has worked well for some time. Recently, I had to replace the thermostat. It now works, if the outside temperature is above freezing. But, when the temperature drops, it freezes everything.

I am puzzled as to why this would happen. Can anyone explain?

[idroba]

If your refrigerator is original 1978 (I don't know the model numbers) than this is probably what is happening. I am also assuming that this is a problem when on Propane, if it is happening on 120 volt power, disregard all of my answer.

Refrigerators of that vintage uses a two level flame system for temp control. When the thermostat calls for the refrigerator to cool, the flame is turned up to the high position. When it is cool enough, the flame is turned down to the low position. There is no pilot light and no electronic ignition turning the flame off totally, it is high flame or low flame.

It is quite common on those types of refrigerators that the low flame has enough heat to cause the refrigeration circuit to keep cooling when the outside temp drops low enough. Then you get freezing, as you have experienced.

Now, why did it change when you changed out the thermostat? I can only guess that in the change out, you wound up cleaning the system enough so your low flame is now producing more heat than it did in the past. So, in fact it is now "working like new" and when new, at low temps those refrigerators very often overcooled at low outside temps, like you describe yours is doing now.

Since only a few RV refrigerators made now use the 'high/low" flame system not too many are familiar with this common overcooling issue that we had in the past.

[RichB]

You are on target. The refrigerator, so far as I know, is the original. I seldom run it on electric, and these problems occurred as I returned to Toledo (27 degrees) from Louisiana (80 degrees). Your explanation fits what I know about the system. I was concerned that I might have a new problem. I am trying to avoid the cost of a new refrigerator, but I no longer know where to find parts.

Thanks for your reply

[RichB]

I just talked to a tech today who said that he did not agree with idroba. He questioned whether the burner on low would generate enough heat to cool. I remain mystified. Any other ideas?

[txtwin]

I started having a similar problem with my fridge during my last trip (oddly enough to Louisiana as well). I have a 2009 model Dm2652. When plugged into electrical power, the fridge is freezing everything solid. Temps were in the 60s/70s during the day, and 30s-50s at night. I have a digital thermometer that I keep in the fridge and freezer for monitoring them, and the fridge stayed around 25 degrees, and the freezer -2.

any ideas?

[idroba]

Originally Posted by RichB

I just talked to a tech today who said that he did not agree with idroba. He questioned whether the burner on low would generate enough heat to cool. I remain mystified. Any other ideas?

Ah well, the tech has apparently not lived with a refrigerator which did that in cold weather. I certainly have, and know others who have experienced the same thing. I am not making it up, it was (is) fairly common with the older two speed flame control system.

As you know, any remote diagnosis of a problem is filled with guess work. That includes the tech's comments.

But, I have given you all I know, and hope you find a solution short of a new refrigerator.

[SSquared]

Also check the fridge light bulb, if it has one. On my 2013 vintage Dometic, the light is a ten watt bulb. The circuit board turns it on to provide heat when needed. I don't know if your older model does this or not.

[JCWDCW]

I found the same problem on an older fridge ('94 Dometic) with the temp outside dropping to high 30s. The low flame gives just a bit too much cooling and the heat loss (actually gain to the fridge) in a cold trailer is not enough to balance the constant but low level cooling. You might be able to dial down the flame somehow.
JCW

[robertbrenne]

I have a 2014 16 Ft. SPORT with a refrigerator that runs on either 115 volts or propane. There are no other settings on the control panel. While we were at the hot New Mexico International Rally, the fridge froze the lettuce when it was running. I was told that there is a plastic clip on the internal fins that adjusts the temp. but have no information in manual for adjustment. does anyone know?

[dregan67]

I had a similar problem with a dometic refrigerator freezing everything after a couple of days on electric. I tried moving the slide on the fins to no avail. So I would just turn the fridge off at night. Not a perfect solution but it worked.
Dan

[Jim J]

For the person with the late model Dometic

That plastic clip thing is attaching the thermistor to the cooling fin. The thermistor changes electrical resistance with temperature. You can choose which fin to put it on and how high or low on the fin. There might also be optional ways to mount the thermistor, closer to the fin or away from it.

Mine was dangling last year after the wife cleaned out the camper and the fridge was not working so good. I found it and experimented with the placement and found the best cooling for me was when it was on the second or third fin away from the wall and on the bottom third of the fin, mounted so it was close to the fin.

If you want your fridge colder try moving the clip to a fin closer to the outer wall and higher, if w you want fridge warmer, move it to a fin in from the wall and down lower on that fin.

[RichB]

Thanks for the suggestions. I have had a couple of techs look at the refrigerator, and it is pretty clear it is the thermostat. The Gas Thermostat. The electric works. So I am now looking for a gas thermostat for a RM 66E. (By the way, when I looked really carefully at the plate, I discovered it is a RM 66E, not a 56E. Kind of corroded!

[RichB]

The problem with the refrigerator was NOT the thermostat. The problem was that the new thermostat had a new bypass screw, which was the orifice used when the thermostat indicated the refrigerator was at temp. The new bypass screw allowed more gas, to cool better in the summer, but it kept the temperature lower in the winter, hence the freezing. Changed the bypass screw, and it fixed the problem. However, had more problems later. If anyone wants a new thermostat, gas or electric for a Dometic RM-66E, let me know.

[nickclifford]

Originally Posted by RichB

The problem with the refrigerator was NOT the thermostat. The problem was that the new thermostat had a new bypass screw, which was the orifice used when the thermostat indicated the refrigerator was at temp. The new bypass screw allowed more gas, to cool better in the summer, but it kept the temperature lower in the winter, hence the freezing. Changed the bypass screw, and it fixed the problem. However, had more problems later. If anyone wants a new thermostat, gas or electric for a Dometic RM-66E, let me know.

Hi Rich, hope you see this, i have1972 fridge that over cools when not so hot outside. It works ok when it's in the 90's but otherwise freezes up the fridge. I'd like a new fridge, but they're now $2k+ wow... so trying to keep this one alive as seen many posts that new ones can be very fickle too. Where did you get the thermostat from ? If that's my issue even .>? thanks

[RichB]

I no longer have any gas thermostats.

At one time this was a very common refrigerator, and I have discovered that RV stores would keep one or two on hand. Look for shops or dealers that have been in business for a long time, and they may have one.

However, the freezing is not related to the thermostat. It is related to a part called the bypass screw, which is an orifice. Those refrigerators operate with a flame. The higher the flame, the more the cooling.

The early models did not cool enough in the heat of the summer, so the solution was to make the bypass screw (orifice) bigger, which made the minimum AND maximum flame be larger. This meant that, in the summer, you could turn up the flame, and it would cool better. But, in the winter, you could not turn it down enough to keep it from freezing.

The solution to freezing in the winter is to change the bypass screw. (Keep the old one for summer.)

After much conversation with Airstream, I finally found one, and had it put in. It took 5 minutes to unscrew the old one, and insert the new. Unfortunately, when I replaced the refrigerator they kept the old one.

I found the bypass screw from Camper Repair Center, 8154 Hwy 22, Montevallo, AL 35115. Sonny Hare is the owner. Work number is 205-665-2531. You can write Sonny, or call, but he has no answering machine and no secretary, so you have to catch him when he is in.

I have searched my records, and I cannot find the part number for the smaller bypass screw, but Sonny will know what you are talking about. If I find my notes, I will post the part number here.

Richard

[nickclifford]

Originally Posted by RichB

I no longer have any gas thermostats.

At one time this was a very common refrigerator, and I have discovered that RV stores would keep one or two on hand. Look for shops or dealers that have been in business for a long time, and they may have one.

However, the freezing is not related to the thermostat. It is related to a part called the bypass screw, which is an orifice. Those refrigerators operate with a flame. The higher the flame, the more the cooling.

The early models did not cool enough in the heat of the summer, so the solution was to make the bypass screw (orifice) bigger, which made the minimum AND maximum flame be larger. This meant that, in the summer, you could turn up the flame, and it would cool better. But, in the winter, you could not turn it down enough to keep it from freezing

The solution to freezing in the winter is to change the bypass screw. (Keep the old one for summer.)

After much conversation with Airstream, I finally found one, and had it put in. It took 5 minutes to unscrew the old one, and insert the new. Unfortunately, when I replaced the refrigerator they kept the old one.

I found the bypass screw from Camper Repair Center, 8154 Hwy 22, Montevallo, AL 35115. Sonny Hare is the owner. Work number is 205-665-2531. You can write Sonny, or call, but he has no answering machine and no secretary, so you have to catch him when he is in.

I have searched my records, and I cannot find the part number for the smaller bypass screw, but Sonny will know what you are talking about. If I find my notes, I will post the part number here.

Richard

great info, many thanks