Dometic DM2852 Not working on AC
Hi, My Dometic DM2852 fridge is not working on 120VAC. I have an LP leak so I have not confirmed that the fridge is working on LP. I am waiting for my new regulator and pigtails to arrive. Any...
Forum Discussion
I figured out what the root cause of the problem. It was a finicky switch on the eyebrow board. I was barely able to remove the eyebrow board from the fridge with the slide outs in. I was standing on a chair leaning towards the fridge and stretching out as far as I could reach. Not the easiest thing to do! I then proceeded to my analysis. Here is what I did:
1. Visual inspection of the board to look for broken traces and signs of EOS (electrical over stress). No problems found.
2. Resistance measurement of all the resistors. No opens found.
3. Diode checking of the zener diode on the board. No problem found.
4. Resistance measurement of both switches. A problem was found.
The Auto/GAS switch exhibited erratic resistance measurements when depressed. It was NOT a short as expected, but a much higher resistance and a borderline open. I then proceeded to take the switch apart. This can be done without desoldering the switch from the board. I should have taken pictures, but I was in a hurry to put this project to bed. I opened up the switch carefully since there is a spring and small contacts on the plunger portion. I performed a visual inspection under my lower power optical mircroscope and found signs of corrosion and tranished metal on the contacts. I gently scraped the tarnished contacts with tweezers and cleaned them with rubbing alcohol. The contacts inside the switch housing were cleaned with compressed electrical contact cleaner since I could not get a cotton swab inside. I then reassembled the switch and verifed that the resistance measurements where now correct. The switch was now acting as a short when the button was depressed.
I then proceeded to reassemble and install the eyebrow board in the RV. After turning the unit ON, I measured the voltage going to the heater and confirmed 120VAC. This showed me that everything was working well. Also the gas relays on the lower control board where no longer switching since the board determined that 120VAC was present.
I let the fridge run over night and the temperatures are as expected. Problem solved! Going forward, I am going to find a source for the switches. My experience shows that cleaned, but once corroded switch contacts might last a long time or they might eventually become a problem again.
In regards to the temps. The measurements were made over 24hrs with the heater on 100% of the time. This will give a much lower temperature than having a refrigerator cycling off and on according to the thermistor based control loop. I also used an infrared thermometer and shined it into the fridge. As I stated, I cannot totally access the fridge due to my slide outs being closed. I can only open the doors by a 1/2". There is no way to put a glass of water in there and measure it thermally. At the end of the day the temperature measurements are what we in the engineering world call "good enough". It shows me that the failure is not in the cooling unit, but somewhere else.
1. Visual inspection of the board to look for broken traces and signs of EOS (electrical over stress). No problems found.
2. Resistance measurement of all the resistors. No opens found.
3. Diode checking of the zener diode on the board. No problem found.
4. Resistance measurement of both switches. A problem was found.
The Auto/GAS switch exhibited erratic resistance measurements when depressed. It was NOT a short as expected, but a much higher resistance and a borderline open. I then proceeded to take the switch apart. This can be done without desoldering the switch from the board. I should have taken pictures, but I was in a hurry to put this project to bed. I opened up the switch carefully since there is a spring and small contacts on the plunger portion. I performed a visual inspection under my lower power optical mircroscope and found signs of corrosion and tranished metal on the contacts. I gently scraped the tarnished contacts with tweezers and cleaned them with rubbing alcohol. The contacts inside the switch housing were cleaned with compressed electrical contact cleaner since I could not get a cotton swab inside. I then reassembled the switch and verifed that the resistance measurements where now correct. The switch was now acting as a short when the button was depressed.
I then proceeded to reassemble and install the eyebrow board in the RV. After turning the unit ON, I measured the voltage going to the heater and confirmed 120VAC. This showed me that everything was working well. Also the gas relays on the lower control board where no longer switching since the board determined that 120VAC was present.
I let the fridge run over night and the temperatures are as expected. Problem solved! Going forward, I am going to find a source for the switches. My experience shows that cleaned, but once corroded switch contacts might last a long time or they might eventually become a problem again.
In regards to the temps. The measurements were made over 24hrs with the heater on 100% of the time. This will give a much lower temperature than having a refrigerator cycling off and on according to the thermistor based control loop. I also used an infrared thermometer and shined it into the fridge. As I stated, I cannot totally access the fridge due to my slide outs being closed. I can only open the doors by a 1/2". There is no way to put a glass of water in there and measure it thermally. At the end of the day the temperature measurements are what we in the engineering world call "good enough". It shows me that the failure is not in the cooling unit, but somewhere else.
