Dometic RM 2852 not working

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USMC_Warrior_0311

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I've used the search function and couldn't find what I needed...

My Dometic stopped working a few days ago. We are in the middle of remodeling it, and have things taken apart, but were cautious with wiring and other things. I had stored some drinks in the fridge and went in to grab one, and the drinks were still "cool" but the fridge and freezer were clearly not working.

The lights on the top for "auto" were on, and the fridge light still turns on but it isn't cooling.

It was rather warm the day I noticed it, so I thought that maybe the coils had frozen but they had not. I turned everything off, waited a day or 2 and went back to it, turned it back on, but still no luck.
I metered the 12v connection at the back of the unit from the outside and had 12.8-13.0, I checked the fuses inside and had continuity and proper voltage at all fuses, so my best guess is that it is toast.

I would rather not pay $1500ish for a brand new one, but even refurbs are going for around $900, and it seems like cooling units alone are going for around $1000...

Is there something else I should be looking for?

Also, it seems like it falls under the recall, but I am not sure if the work has been completed already, or if there was never an issue

Thanks for advice/help
 

DonTom

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Okay, it does not work on 120 VAC but does it work on propane?

Turn "auto" off and see if it works on propane ("gas").

If it does, turn "auto" back on.

Next step would to see if you have 120 VAC is on the two wires on the control board that go to the heating element. If you have the 120VAC there, you have an open heater element. If you do NOT have 120 VAC there, you need to find out why. It's a simple circuit. Simply your 120 VAC goes to the heater element via the control board. Of course, check that you have 120 VAC on the refrigerator outlet first.

-Don- Reno, NV
 

Gary RV_Wizard

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Unlike a compressor fridge, an RV absorption fridge can't "freeze up".

Start with Don's suggestions. Measure the temperature in the freezer to detect if there is any cooling at all. A thermometer in a glass or bowl of water will give accurate temperature readings. Even if you are getting some cooling, e.g. the freezer drops to 50 degrees in either mode, odds are the cooling unit has failed. They aren't repairable.

Reaching in to the back via the outer access door, the tubing of the cooling unit leading down to the boiler (the fat reservoir near the lower middle) should be warm-hot but not blistering. If you test with your fingers, be careful!

You can a free service manual and service tips at Dometic RM2852 – PDX RV
 

USMC_Warrior_0311

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120v in, 12v out, no fuses blown, don't have any lp at the moment so I'll have to test that later.

The tubing was warm this morning, but not blistering hot
 

Lou Schneider

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Try aiming a small fan to blow upwards on the external tubing. The fridge relies on a chimney effect to draw heat up and away from the coils, when the air temperature approaches the temperature of the tubing there isn't enough difference to set up the thermosiphon. It doesn't take much airflow, but you need some across the coils.
 

DonTom

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120v in, 12v out
Should be 120 VAC in, 120 VAC out to the heater element when on "auto". The control board simply has a relay to put 120 VAC on the heater element.

When on "auto" If you have 120 VAC on the heater element and it doesn't heat you have an open heater element. If you do not have the 120 VAC, you have a problem in the control board.

I think it is J7 & J8 on the control board that goes to the heater element.

See the info here.

-Don- Reno, NV
 

USMC_Warrior_0311

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Sorry for the mis guided info there...

I had measured across other areas...

I have 120v in, and 120v out at J7 and J8.

The manual says the ohms should be 44, I have a reading of 44 very briefly and it settles at about 38, the manual says it can have a tolerance of +/- 10% so I am a little below that
 

USMC_Warrior_0311

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I just tested the AC volts at the main DC terminal block and it shows close to 29 volts. The tolerance according to the manual is 6

What does that mean?
 

USMC_Warrior_0311

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"If AC volts exceed 6 on the DC incoming line the power source should be cleaned up. AC voltage in excess of 6 volts will affect the processor and create erratic operation. When testing for AC ripple on the DC line put a load on the converter"

What does it mean by the power source should be "cleaned up"
 

DonTom

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What does it mean by the power source should be "cleaned up"
It needs to be filtered. Perhaps there is an open capacitor. Or a worse case can be a shorted diode in a bridge rectifier or whatever, which can then destroy capacitors.

How high is the DC voltage there? But six volts is a lot of ripple on any DC supply.

But if you have 120 VAC and 38 to 44 ohms resistance on the heater element, that should work. Be sure you get NO ohms reading from either of the disconnected J7 & J8 to the frame (with the refrigerator AC unplugged, of course).

If all that checks okay, maybe what Lou said about not enough air circulating around there. I do not see how it cannot work if you have that 120 VAC across that ~40 ohm heater element, but there is one more possibility. Perhaps it opens when it has 120 VAC on it and starts to get hot and then opens. Do you have a way to measure the refrigerator AC current? If it looks okay for a few seconds and then drops to nothing, you found your problem.

A killowatt meter would be good for such a test.

-Don- Reno, NV
 

USMC_Warrior_0311

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It needs to be filtered. Perhaps there is an open capacitor. Or a worse case can be a shorted diode in a bridge rectifier or whatever, which can then destroy capacitors.

How high is the DC voltage there? But six volts is a lot of ripple on any DC supply.

But if you have 120 VAC and 38 to 44 ohms resistance on the heater element, that should work. Be sure you get NO ohms reading from either of the disconnected J7 & J8 to the frame (with the refrigerator AC unplugged, of course).

If all that checks okay, maybe what Lou said about not enough air circulating around there. I do not see how it cannot work if you have that 120 VAC across that ~40 ohm heater element, but there is one more possibility. Perhaps it opens when it has 120 VAC on it and starts to get hot and then opens. Do you have a way to measure the refrigerator AC current? If it looks okay for a few seconds and then drops to nothing, you found your problem.

A killowatt meter would be good for such a test.

-Don- Reno, NV
The DC voltage is 13.8 ish... In the manual, it says 6 volts of ripple is acceptable. But, why would it be at 29?

I didn't try resistance from one to the frame... I can do that tomorrow.

I have had a fan on it, still no luck.

It did say plus or minus 10% for the ohms and it is closer to 15% on the minus.

What do you mean refrigerator AC current? I have an ohmeter, which is what I have been using to test everything else.
 

DonTom

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The DC voltage is 13.8 ish... In the manual, it says 6 volts of ripple is acceptable. But, why would it be at 29?

I didn't try resistance from one to the frame... I can do that tomorrow.

I have had a fan on it, still no luck.

It did say plus or minus 10% for the ohms and it is closer to 15% on the minus.

What do you mean refrigerator AC current? I have an ohmeter, which is what I have been using to test everything else.
If you have 120 VAC on the heating element and 15% off in resistance (ohms) , it should still work fine, but there is a chance that when the AC is applied and and the heating element heats up a little, it opens and goes cold before the refrigerator can cool down. The DC stuff has NOTHING to do with your problem if 120 VAC is getting to that heating element. Perhaps it causes other problems, but NOT that. 120 VAC across the heating element is all that is required, along with a reasonable load of the heater element. You have both, so for now, forget about those DC measurements, they have nothing to do with your main problem.

It is very unlikely that being 15% off instead of 10% will cause a problem. It could make some difference, but not enough for it to stop working completely, but. . .

But cold testing with an ohmmeter is sometimes a waste of time. It can always tell you it's bad by a far off reading, but often will check good on an ohmmeter and still have a serious problem. That is why the amp or KW meter is used. It checks the REAL world stuff as it is really trying to work, something that an ohmmeter cannot do.

-Don- Reno, NV
 
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DonTom

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The DC voltage is 13.8 ish... In the manual, it says 6 volts of ripple is acceptable. But, why would it be at 29?
BTW, I don't even believe those readings. Or the manual.

I think your measuring millivolts instead of volts or something like that. Six volts AC ripple on 13.8 VDC would NEVER be acceptable on anything, period.

Can you tell me what model voltmeter you're using and which scale?

And can you post a quote of what the manual says in the exact words about six volts ripple?

There is something there that is incorrect.

However, it doesn't have anything to do with why your heater element isn't working. It only requires 120 VAC which you say you have there.

-Don- Reno, NV
 

USMC_Warrior_0311

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BTW, I don't even believe those readings. Or the manual.

I think your measuring millivolts instead of volts or something like that. Six volts AC ripple on 13.8 VDC would NEVER be acceptable on anything, period.

Can you tell me what model voltmeter you're using and which scale?

And can you post a quote of what the manual says in the exact words about six volts ripple?

There is something there that is incorrect.

However, it doesn't have anything to do with why your heater element isn't working. It only requires 120 VAC which you say you have there.

-Don- Reno, NV
I posted the direct text from the manual above, but here it is again.

"If AC volts exceed 6 on the DC incoming line the power source should be cleaned up. AC voltage in excess of 6 volts will affect the processor and create erratic operation. When testing for AC ripple on the DC line put a load on the converter"

I have a journeyman's license in residential 120v, but have never really done much with 12v systems, so some of the info in here is chinese to me...

I am using a Klein meter, set to read up to 200v AC, so the reading from my ohmmeter is correct.

I apologize for the mix up last night, I was exhausted and misread you asking me to measure the current and not the voltage haha
 
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USMC_Warrior_0311

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ok, got some more readings from the ammeter. Around the cord of the fridge registered .007A at the highest and that was momentarily.

Now I am not showing AC voltage across the DC block. If any, it is extremely low...

I only had an OL reading when checking resistance from J7 or J8 to the frame.

When the J7 and j8 lines were disconnected from the mother board the voltage test across them read 0, but the male ends on the motherboard read 120v.

Tonight is the first time I have seen the "Check" light on on the fridge.

The light inside the fridge is still on (not sure if it is 12v or 120v.

The heater coil was warm-hot today, I could still hold my hand on it, but it was definitely warmer than the other day.

Thanks again for all the help, this is getting frustrating.

I found a "used" fridge at an RV junkyard that they want $900 for... sheesh
 

DonTom

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ok, got some more readings from the ammeter. Around the cord of the fridge registered .007A at the highest and that was momentarily.

Now I am not showing AC voltage across the DC block. If any, it is extremely low...

I only had an OL reading when checking resistance from J7 or J8 to the frame.

When the J7 and j8 lines were disconnected from the mother board the voltage test across them read 0, but the male ends on the motherboard read 120v.

Tonight is the first time I have seen the "Check" light on on the fridge.

The light inside the fridge is still on (not sure if it is 12v or 120v.

The heater coil was warm-hot today, I could still hold my hand on it, but it was definitely warmer than the other day.

Thanks again for all the help, this is getting frustrating.

I found a "used" fridge at an RV junkyard that they want $900 for... sheesh
120 VAC times .007 amps is 0.84 watts. That's not going to work. You should be around 325 watts, which is a lot closer to 2.7 amps (120 VAC times 2.7 amps = 324 watts) Be sure you had the refrigerator on "auto" and plugged in normally and everything connected when you measured that.

See if you can measure the AC voltage from J7 to J8 while the heating element is still connected. Be careful, as that should be the full 120 VAC. I am thinking you have a burnt trace on the control board or perhaps a bad relay. If that heater element voltage is very low, it is not going to work. Be sure you have the refrigerator on "auto" for any AC operation testing. Also, if you can, measure the AC current from the control board to J-7, leave J8 connected as normal. See if you still have that .007 amps. If it really has the 120 VAC across J7 & J8 and the current at the element is really only drawing .007 amps, you have a bad heater element regardless of any ohms reading on the heater element during a cold test.

The check light will only come on when trying to use propane but when the burner cannot light, such as when your propane is turned off. Sometimes when the propane is on, it takes a few minutes for the propane to get to the refrigerator. When the check light is on, the refrigerator is NOT getting the propane or the burner is not getting lit for another reason , such as no spark. Turn off and on the refrigerator to clear the check light. You should be able to hear the sparks when outside near the rear of the refrigerator until the check light comes on when on "gas". After a minute or so of not being lit, the check light comes on. This is most likely NOT related to your 120 VAC problem. Gas works much differently than 120 VAC operation.

If on propane, and on "auto" it will switch to AC operation when it detects you have AC. You should never get a check light when on AC operation. But if there is no AC, it will automatically switch to propane and if it cannot light on propane, you then get a check light. Reset by turning refrigerator off and on again and it will try again, first looking for AC, no AC then switches to propane. No propane and then you get a check light.

On 120 VAC is it a very simple circuit, get 120 VAC on the heating element and it should work on AC. The 120 VAC simply goes through the relay on the control board to put the 120 VAC on the heater element (refrigerator must be on "auto" for AC operation).

"If AC volts exceed 6 on the DC incoming line the power source should be cleaned up. AC voltage in excess of 6 volts will affect the processor and create erratic operation. When testing for AC ripple on the DC line put a load on the converter"

Sounds like a mistake in the book. It must have meant 6 millivolts. I cannot imagine any DC power supply having 6 AC volts of ripple and being considered acceptable on any DC power supply for anything.

-Don- Reno, NV
 

Old_Crow

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I've bought several big ticket items from RV wrecking yards. Their prices on those are generally around 50% of the new cost. Smaller items(cabinet handles, switches, light fixtures)are generally less(often dirt cheap).
 

DonTom

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I've bought several big ticket items from RV wrecking yards. Their prices on those are generally around 50% of the new cost. Smaller items(cabinet handles, switches, light fixtures)are generally less(often dirt cheap).
IMO. there is no reason to replace a refrigerator that doesn't work on AC. It is cheap and usually easy to fix no matter what the cause. Besides that, it can be ran on propane 100% of the time even when there is AC available.

AC operation is simply a control board putting the 120 VAC on the heating element. Shouldn't be expensive or difficult to repair, with one possible exception. The problem that I had where it was very difficult to get the defective 120 VAC heater element out of the tube and the new one back in. But it normally isn't that much trouble.

-Don- Reno, NV
 

USMC_Warrior_0311

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I got these messages a little too late, haha...

I gave up in troubleshooting and picked up a new (used) fridge...

It will get installed in a few days when I have the time.
 
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