Fridge Flue Temperature

[Travelin2]

We recently bought a 2003 Pleasure-Way van. It has a Dometic RM 2353 fridge with two side-wall vents for draft. It is the manual model with a Piezo igniter. It is a 3-way. To check the fridge operation, with a thermometer in the refer' area reading 70*, I turned it on 120 AC operation mode overnite with the rotary temperature control on "MAX" and the next morning the main food storage area was at 32 degrees so I figured it was going to be fine. I turned it off and let things warm back up to ambient. To check the 12V operation I didn't let it run long enough to cool the fridge because I didn't want to kill the battery but I connected a volt meter to the battery and when I switched on the 12V mode the battery voltage immediately started steadily dropping, indicating an amperage draw. I also touched the heating element and it was hotter than H&ll! That element lays right beside the 120AC element so I figured that system would work but would confirm on a trip while running the alternator.

So, now it was time to check it on gas. I started again with the refer' area at 70*. I turned the rotary control to gas, held in the "gas-on" button and pushed the Piezo sparker. I had lit the cook top burners previously to purge the gas line but I was still pleasantly surprised when the little flame indicator jumped up after only the second click. I had the "temp" setting at "MAX" and after about two hours the thermometer in the fridge was only down to 54*. I could feel considerable heat coming out of the upper sidewall vent. I checked some temps with an IR gun and I found a whopping 400 degrees when checking on the little deflector plate right over the top of the flue tube. Down by the burner I found 160* or so on the base of the stack. Up the stack on the outside of the insulation it was only around 120*. I had heard in the past that over heating the cooling unit can wreck it and that 400* reading surprised me that it was that high so I shut it down. I could find nothing anywhere about what temperature to expect.

This fridge is fairly old but has been used little. Mostly sitting idle not being in service. I'm in Florida and I had noticed immediately that there were no bug screens on the vents so to make sure the mud dobbers hadn't plugged things up, I removed the top deflector, pulled out the spiral baffle hanging on a wire in the flue and used a mirror and flashlight to look down the "barrel". I was pleased to see that it was clean as a whistle with no rust and appeared to be lightly galvanized or something similar. The bottom of the baffle was discolored due to heat. I removed the burner shroud to have a look at the flame and it looked fine. Nice consistent blue, well defined flame.(I will try to attach a picture)

Opinions and thoughts on the operation of this would be welcome. I'm wondering...
1. Do I dare run it for a long time with that 400* flue temp?
2. What is the expected flue temp?
3. How long should it take for the gas system to bring the refer
section down to 38* or so?
4. If it is cooling on 120AC does that mean I don't have the
dreaded "crystal build-up/blockage?
5. If there is some crystal buildup inside the cooling unit
will running it for long periods on 120AC dissolve them back into
solution and improve performance?

[Travelin2]

dougrainer wrote:

Travelin2 wrote:
Thanks for that doug. Makes sense.

AND, the older Bypass Refers did NOT require a Power Source to run and cool. Just a constant supply of LP. Doug

I never gave that a thought but I see what you mean, the piezo sparker is self sufficient so you could run the fridge with the disconnect switch off. Course then you would have no gas sniffers working. I think I finally got the picture thing figured out. This is the rig you helped me with. You can see the vents are not that far apart.

[dougrainer]

Travelin2 wrote:
Thanks for that doug. Makes sense.

AND, the older Bypass Refers did NOT require a Power Source to run and cool. Just a constant supply of LP. Doug

[Travelin2]

Thanks for that doug. Makes sense.

[dougrainer]

Travelin2 wrote:

Chris Bryant wrote:
From the pics, that install is not great. The space should be baffled to the condenser (top) coils, so all air has to flow over them. The spec is now pretty much zero clearance to the back.

Thanks for chiming in Chris. I have been reading a lot of old threads about fridges including numerous posts of yours and other who have helped me here. I have learned a lot.

I did read some threads concerning the distance between the coils and the enclosure. Mine measures 4 inches air gap. I will take you advice and fabricate a baffle. I think I read somewhere that cutting a piece out of a section of galvanized AC ducting pipe works well.

I do have a question that you probably have the answer to. This older fridge is of the manual ignition (Piezo) type so the unit does not have the ability to shut down the heating flame and reignite it. So, that being the case, when running on gas and the fridge reaches the desired level of coolness, like on setting #4 on the knob, how does the unit cut down on the cooling effect applied to the freezer/refer area of the refridgerator?

Older LP refers have a BYPASS Tstat. When the temp is reached, the Tstat drops the LP flame down to what some will call a "pilot" flame. Too small to percolate but enough to stay running. Doug

[Travelin2]

Chris Bryant wrote:
From the pics, that install is not great. The space should be baffled to the condenser (top) coils, so all air has to flow over them. The spec is now pretty much zero clearance to the back.

Thanks for chiming in Chris. I have been reading a lot of old threads about fridges including numerous posts of yours and other who have helped me here. I have learned a lot.

I did read some threads concerning the distance between the coils and the enclosure. Mine measures 4 inches air gap. I will take you advice and fabricate a baffle. I think I read somewhere that cutting a piece out of a section of galvanized AC ducting pipe works well.

I do have a question that you probably have the answer to. This older fridge is of the manual ignition (Piezo) type so the unit does not have the ability to shut down the heating flame and reignite it. So, that being the case, when running on gas and the fridge reaches the desired level of coolness, like on setting #4 on the knob, how does the unit cut down on the cooling effect applied to the freezer/refer area of the refridgerator?

[Chris_Bryant]

From the pics, that install is not great. The space should be baffled to the condenser (top) coils, so all air has to flow over them. The spec is now pretty much zero clearance to the back.

[Travelin2]

Thanks to all you guys that helped me out here. I tried to post another pic but for some reason it won't accept it.

[Old-Biscuit]

Put your temp gun AWAY..........

Unless you fully understand the absorption cooling process you are just reading numbers which have no meaning to you

Buy the way.......all temp readings are good

Fridge is functioning as designed.


For your reading pleasure

[Gjac]

John, every thing looks fine from you pictures and what you posted. I sure your refer will be below 38 or lower by morning. From your post it looks like you have a class B. How do you level it? That is the only thing that I would be concerned about.

[Travelin2]

Gjac...I'm attaching a photo so you can see that I don't have a roof vent, just an upper and lower side vent so its easy to reach the components. It has been running about 4 hrs now and it is down to 44 degrees so maybe the critter is going to be alright.

doug...thanks for posting those numbers. Makes me feel like maybe I'm not going to melt things down after all. I went out and measured down 8 inches from the top of the flue and checked the temp.


Then I checked the temp of this tube in two places, Does that temp difference spell good or bad?

[dougrainer]

Normal operating temp of the Flue/boiler area is 350 degrees give or take. The TRIP or lock out on Refers that have overtemp/recall controls is 700 degrees. You will get 700 plus if run OFF level or the ventilation is blocked or the Ammonia has leaked out of the Cooling Unit. The temp at the Chimney is not a concern. The Temp in the first 8 inches from the top of the burner is the temp you need to test. THAT is where the highest heat concentration is. There is a Spiral baffle right above the LP flame to disburse the flame around the round chimney to heat the boiler. If you did not have that baffle, all the heat from the flame would go straight up the chimney and never heat the boiler. Doug

[Gjac]

I have a Norcold 682 but it sounds like you got on top off your roof and shot the plate at the very top of your flue. I never checked mine there but I would expect that to be quite hot. I measured about 120 on mine on the out side sht metal in that same area. I don't think you have a problem. Let your propane run overnight, I believe your refer temps will be the same as you saw on electric. Do you have a way to level your RV?

[Travelin2]

trying to add a picture...

[Travelin2]

I started the fridge up on gas again about a half hour ago. The 400* reading I got yesterday was on the hottest part of that little tin 90 degree deflector plate that slides over the top of the flue tube. I just now shot it again and after 1/2 hr it is reading 375 at the hottest spot I can find. When I check 4 inches up from the bottom of the stack on the tin surrounding the insulation, it reads 108. This is right in the area where the 120 and 12 volt heat probes are.