Dometic fridge woes.

[btcruzer]

I have a Dometic model RM2453 3-way fridge that works in all 3 modes but the LP mode is a problem. It always ignites and burns clean. However I don't believe that the flame is hot enough. I've always heard that LP mode usually cools better than electric and that has been my experience with several different RVs. But this one is different.
This model does not use a "pilot Light" - instead it has a thermostat controlled gas valve with two passages. One is the bypass that allows a small flow of LP to flow in order to maintain the pilot light. The other is is the full flow passage that should cause a larger flame when the thermostat calls for cooling. The thermostat also controls a simple off/on switch in the electric mode. I have tested the electric side and determined that the thermostat does turn the electric on and off as needed.
I have measured the temp of the boiler tube at the same spot (just above the top of the flue) in both electric and LP mode. Electric is hotter.
The thermostat has 9 settings -
OFF ( not really off but bypass mode)
1 through 7 are temp settings - 1 warmest and 7 coldest
MAX is full time operation not controlled by the thermostat.

I've read that there is a visible difference in the flame height in the bypass and full operation. I have observed the flame while in the OFF position (bypass mode) and then someone switching the thermostat to all the other settings. No difference. I've also heard and observed that you can hear the flame. Not this one.

The burner assembly has been removed and cleaned several times. The jet (#43 per Dometic) has been removed soaked, cleaned and blown dry several times. The flue has been swabbed full length several times.

I have replaced the 2-stage LP regulator. I have measured the LP gas pressure with a manometer. Initial pressure was 13 inches of water. Dometic manual says 11 inches. Adjusted pressure and observed pressure for probably an hour in operation -- never varied.

I replaced the thermostat. No change.

I am out of ideas. The LP pressure is taken within an inch of the jet. Seems to me that the proper pressure through the specified jet should produce the full flame. What am I missing?



I'm convinced that the ther

[dougrainer]

btcruzer wrote:
Doug The burner assembly has been removed and cleaned several times. The jet ( orifice ) (#43 per Dometic) has been removed soaked, cleaned and blown dry several times. The flue has been swabbed full length several times.

The flue has been swabbed. OK. What was the condition of the Baffle?

[enblethen]

Make sure the shaft connecting the valve to the fuel selector knob is tight and turning the valve completely open.
Could take valve out and try to spray through it with brake cleaner.

[btcruzer]

Doug The burner assembly has been removed and cleaned several times. The jet ( orifice ) (#43 per Dometic) has been removed soaked, cleaned and blown dry several times. The flue has been swabbed full length several times.

[dougrainer]

Have you remove the Orifice and blown it out with air?. I usually spray Carb cleaner in the orifice hole and then use compressed shop air to blow it out. Since you have replaced the ONLY real component, then the orifice partial blockage would be the next thing. Doug

PS, have you pulled the spiral baffle and verified it is OK and not deterioated? That Baffle is required for correct Heat disbursement from the flame.

[btcruzer]

Dougranier -- the LP pressure was measured at the port next to the orafice - 11 inch WC per the manual. same pressure at any setting of the thermostat. Didn't examine the filter on the new thermostat prior to installation. Hard to imagine it could become plugged at initial use. Also the same problem with two thermostat -- odds seem high.
I guess I did a version of your water temp test. I connected a small test light to the power leads of the heater element. Switched to electric mode and observed for several hours. the light would cycle on/of indicating to me that the thermostat was doing what it is supposed to do - control the temp. The fridge did cool and maintain a stable temp.
The same movable piece in the thermostat that controls the electric switch also moves the plunger that controls the gas flow at the same time. I cannot verify that the larger gas passage in the thermostat is actually opening. I can only assume a NEW thermostat is properly adjusted for its intended use.
I'm thinking that there must be a restriction somewhere. but the lines and passages are so tiny it is hard to imagine. With the small amount of gas required would a restriction actually lower the LP pressure at the test port? Seems it would have to be after (downstream) the thermostat. The only device other than tubing between the thermostat and orafice is the safety valve that bypasses the thermocouple. That actually looks like a likely place.
Unfortunately the fridge is back together and installed. All the controls are on top and hidden until the fridge is disconnected and moved out of the hole.

[btcruzer]

Emblemthen ... no. you are correct. your PDF is for a RM 2354 but mine is a different fridge....

[btcruzer]

Emblemthen ... no. you are correct. your PDF is for a RM 2354 but mine is a different fridge....

[btcruzer]

Emblemthen ... no. you are correct. your PDF is for a RM 2354 but mine is a different fridge....

[enblethen]

Dam auto correct!

[btcruzer]

The main and only regulator was replaced a couple of weeks ago. during this problem. Lp pressure measured after replacement.

[btcruzer]

ENABLETHEN...ha. you had me going there for a bit. Mine is mode RM 2453 NOT RM 2354..and yes a #43 jet.

[enblethen]

Must be two versions.
RM2354 Parts breakdown
When was the main regulator last replaced?

[dougrainer]

1. The Correct way to verify the LP pressure is at the Port just behind the Orifice. THAT will tell you if the Tstat is allowing the full 11.5 inches WC to the burner. When in BYPASS mode the Pressure will drop to Pilot flame pressure.
2. FILTER A filter is located in the inlet fitting to the thermostat. The filter can become saturated and cause a restriction to gas flow. If you suspect a restriction, first verify the thermostat and bypass screw are good. THERMOSTATLP GAS MODE The thermostat is calibrated by the manufacturer so that at mid-range the cabinet temperature should be approximately 40 degrees Fahrenheit. To check the calibration of the thermostat, place a container of water in the cabinet of the refrigerator and operate at mid-range setting until the thermostat is satisfied. Check the temperature of the water. It should be approximately40 degrees. To check the thermostat for proper g a s flow, set the thermostat to maximum and check the gas pressure at the pressure test port. It should be line pressure, between water column. If you have less than 11 inches of water column pressure, the next step would be to shut off the gas supply and remove the bypass screw. Then install a bypass screw that does not have the small o-ring on it. Next, turn on the gas supply and take a reading. If the manometer now reads 11 inches of water column, the thermostat is defective and must be replaced. If the bypass screw test shows no change in pressure, the problem lies in the filter, the shut-off valve or the gas supply.
3. Since you have replaced the tstat, That FILTER is what I would suspect is the problem. Also, are you POSITIVE that you did not kink or break the Metal Sensor Cappillary tube that runs to the Evaporator fins? If it loses its gas charge it will cause your type problem.

[btcruzer]

this fridge does not have an electruc gas shut off valve.Only shutoff is a manual cutoff at the LP line.

[enblethen]

Have you measured the 12 volt DC at the gas valve?