Dometic RM 8505 Refrigerator – Partial Cooling on Propane

[Chuck_Sorensen]

On a recent camping trip our refrigerator went into a partial cooling mode while on propane. 120 vac and 12 vdc worked well. After our local Dometic Service Center serviced the unit it was again cooling properly; but no cause for the previous partial cooling was identified.

I checked the unit in our driveway over the next week; it cooled just like it had for most of the past two years; great. What I saw when things seemed to be working correctly: A full blue flame that filled the observable space in the burner. The flame would stay full until the selected refrigerator temperature was reached, and then it would shut off for a while. When the box temperature came up a couple of degrees, the flame would be reignited and run until the selected temperature was again reached. For the conditions when monitored the flame was on full for 1 hour and off for ½ hour. The condenser fans would cycle on and off. The upper flue temperature was typically 400 degrees F. while the flame was burning.

Mid June, we headed off on a camping trip and after 3 days the unit was back to 27 degrees F. in the freezer and the refrigerator drifting around in the 50’s depending on the outside temperature. We bought an ice box to continue our trip.

On returning home, I started the refrigerator many times. It was not cooling enough. 27 degrees F. in the freezer and the refrigerator section in the 50’s depending on the outside temperature. The burner flame was about half the size of the full good working flame. The burner never shut off. The condenser fans never ran. The selected refrigerator temperature setting was never reached. The upper flue temperature was typically 350 degrees F. and lower. Not enough heat to push things around the closed system.

On one last start up of the refrigerator, the flame came on large and the flue temperature was around 400 degrees F. I left it running over night and in the morning, the refrigerator section was at 22 degrees F. and the full flame was still going. The blue LEDS in the refrigerator were flashing; do not know if it was too cold for them or the control system was having problems. I tapped on the refrigerator’s gas valve and the flame immediately dropped back to its half size with an eventual flue temperature of around 350 degrees F. The refrigerator settled back into its 50’s degree F. range; the failure mode.

Dometic would not let me talk to a technical person so that I could find out more about the gas valve assembly and how it is controlled.

Chuck Sorensen
Buellton, California
2012 PW Excel TS

[NCWriter]

Thanks for posting the follow-up, Chuck. Even though problems are a pain to deal with, I've started to embrace them (after the fact) because we get to know our RV's ways and potential issues. Good stuff you learned and passed on to others who can use it.

We bought a used 2006 Class B in 2010 and the seller was slightly vague about using his fridge on propane. Sure enough, we had issues with it (no probs on 12v or shore power.) RV repair places were clueless and offered to install a new fridge ($$$!!) but we ended up ordering the parts from Dometic ourselves and it was a fairly easy fix. Now we know more about the fridge. (And last year we learned why waste tank seals don't like freezing mornings. But that's another story.)

[Chuck_Sorensen]

Thanks, Al -

I did not pay much attention to the refrigerator for the two years that it faithfully cooled our food. When the refrigerator went into its partial cooling mode, I did not know what was normal when I pulled the two related van side vents off.

One of the first things I found is that when looking on the web, most of the burners were larger than the one in my refrigerator; small stuff; harder to clean. When a shop services a burner, the gas jet is inspected and cleaned along with the other things. Cleaning did not fix the cooling problem. Changing out the refrigerator propane valve assembly restored normal burner flame and cooling.

I am not good at seeing burner flames during the day. In the evening, when my burner is full on, the blue flame fills the visible burner area; even below the burner parts sticking in there. When the refrigerator was not cooling well, the flame was smaller and better defined; down to almost half of the flue diameter. Sound of the burner turned out to be a good guide, also.

Wanting a better handle on what was a “good” flame, I used a meat digital thermometer to measure the flue exhaust at the top of the flue before the exhaust is directed toward the van side vent. For my Dometic RM 8505 that was around 400 degrees F. Typical temperature during partial cooling was 350 degrees F.

As a rough check, for good gas or electric operation I lick my finger and transfer the moisture to the top side of the condenser inlet tube just before the fins start; all of the moisture is evaporated within 4 seconds. The condenser cooling fans did not run with partial burner flames.

There are a lot of different refrigerators out there so your normal may be different than mine. I now have a better idea of how hot and warm cooling system components should be during normal operation.

Chuck Sorensen
Buellton, California
2012 Excel TS

[Fastpaddler]

Thanks. Most helpful for us all to know what can happen. Glad all is well now.
Al

[Chuck_Sorensen]

My partial cooling to various temperatures inside the refrigerator while running on propane was cured by Dometic first replacing the burner control module and then the propane gas valve assembly. When the new valve was installed, every start up since has produced a full burner flame and enough heat for proper cooling.

Chuck Sorensen
Buellton, California
2012 Excel TS

[Chuck_Sorensen]

Hi Arizona Kid -

This is more of an FYI of what can happen to this refrigerator.

Thanks -

Chuck

[Arizona_Kid]

I would ask Admin to move this to Tech Issues lot more help over in that forum.