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Old 06-16-2011, 11:33 PM   #1
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Cooling problem on gas

I just had a new Dometic 2852 refrigerator installed before a 3-week trip up north. Before the trip, I adjusted the thermocouple on the inside fins to set the temperature at about 35 when running on AC power.

At Alumapalooza, with the temperatures in the 80s, the best I could get running on gas was about 44 inside . Since arriving home, I have found that gas operation only lowers inside temperature about 40 degrees.

In the last several days, I have tried both AC and gas operation for 24 hours alternately several times with the doors kept closed and a remote temperature probe inside:
  • AC operation for 24 hours - ambient 102 in daytime, 70s at night -inside temp = 35 degrees
  • Gas operation for 24 hours - ambient 104 in daytime, 70s at night - inside temp = 68 degrees.

Switching from gas to AC operation starts to cool the box down within a few minutes.

The gas flame looks great; as nice a flame as I have observed on my prior Dometics. The stack is hot to the touch and the Snyder cooling fan is running which says that the tubing is hot where the thermostat is attached.

I think the only thing that could possibly explain this problem would be that the spiral flue baffle may be missing. This would allow the heat to simply pour out the top of the stack without much heat transfer. Unfortunately, the baffle can not be seen and I will have to either pull the fridge to check or tow the 120 mile round trip back to Camping World to have them address the problem.
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Old 06-16-2011, 11:59 PM   #2
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Can you use an inspection mirror to see up in the flue. .You could have too much air flow behind the refrigerator. There is only supposed to be about an inch of space from the wall and the coils. Airstream has a curved wall and some are installing a baffle plate to close up the space. There was a thread on the main portal with a diagram of how to place it.
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Old 06-17-2011, 12:17 AM   #3
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Can you use an inspection mirror to see up in the flue. .You could have too much air flow behind the refrigerator. There is only supposed to be about an inch of space from the wall and the coils. Airstream has a curved wall and some are installing a baffle plate to close up the space. There was a thread on the main portal with a diagram of how to place it.
The baffle is in place, just as it was in the original fridge. If air flow was the problem, it would not cool on AC power. Gas, theoretically, should cool faster than AC since it provides more BTUs.

I tried the mirror trick, but I could not see anything. I don't know how far the baffle should be from the burner, but there is nothing in the first inch or two.

I also tried putting a camera up to look at the top of the stack to see if the pull ring on the baffle was there. That did not work either; too restricted and too dark.
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Old 06-17-2011, 10:40 AM   #4
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Originally Posted by Pahaska View Post
The baffle is in place, just as it was in the original fridge. If air flow was the problem, it would not cool on AC power. Gas, theoretically, should cool faster than AC since it provides more BTUs.

I tried the mirror trick, but I could not see anything. I don't know how far the baffle should be from the burner, but there is nothing in the first inch or two.

I also tried putting a camera up to look at the top of the stack to see if the pull ring on the baffle was there. That did not work either; too restricted and too dark.
John
I would think that the BTU value should be about the same by design. Is the burner assembly lined up correctly. You might try moving it some. Good luck I haven't dealt with mine in several years.
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Old 07-06-2011, 07:59 PM   #5
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Same Woes

John,
We had the same issue this past weekend at the Birthday Bash II. We have a Dometic RM3862 in our '06. On 110V it kept the refrigerator at 42 F with the cooling button on "3". Once we switched to gas, becuase we were boondocking, it had trouble keeping the refrigerator compartment in the high 40s low 50s with the cooling button on "5". Funny thing is the freezer was plenty cool and the outside temperatures were in the mid 80s during the day and we were in the shade. As soon as I started the generator and ran it on 110V the temperature fell quickly. I checked everything I could think of; burner tube, obstruction in the flu, ventilation, etc... I also moved the thermistor up and down on the fins and that seemed to have little to no effect either. So I guess I am going to have to bite the bullet and have the RV dealer take a look at it when I have it in this month for the PA state safety inspection.
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Old 07-06-2011, 08:42 PM   #6
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As I understand it, the problem is caused by the lack of adequate air flow along the curved wall of the AS. I had heard of installing a small computer type fan at the bottom of the refer compartment to assist with upward air flow.

I acquired a small 12 volt fan and mounted it on stand-offs about 1 inch off the floor of the compartment at the back of the refer. The refrigerator now cools equally well on gas and electric. I surmised the extra heat made by the burner was not venting well and added more heat load for the cooling system to overcome on hot days in the sun.
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Old 07-06-2011, 09:05 PM   #7
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John, I had one come in a few months back with this problem, and it turned out to be a restriction in the gas flow. The flame looked good, but it wouldn't cool. Turned out the LP line had gotten pinched.
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Old 07-06-2011, 10:36 PM   #8
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I haven't attacked the problem further due to other business, but I think I may either have some clogging in the nozzle or else a low pressure from the regulator.

It is definitely not airflow. That would affect 110 v operation just as much as gas and 110v operation is super good. Besides, I have a Snyder fan kit on the rear fins and that gives super airflow. I can hear the fan running on gas operation. There is heating, just not quite enough.

I intend to pull the nozzle this week and clean it with alcohol. If that doesn't solve the problem, I'll get the regulator pressure checked. There is definitely no kink in the line.
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Old 07-07-2011, 08:32 AM   #9
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Service Manuals

I found a link to the service manuals that may help the more technically minded Airstreamer.

Dometic refrigerators - Download Dometic Manuals

Pick your model from the range at the bottom of the page.

I downloaded the manual for my RM3862 and have been reading the proposed solutions to weak cooling on gas.

The first thing I am going to try is to soak the orifice in isopropyl alcohol to see if that help. Of course we don't have any in the house so I will have to run out and get a bottle.

I will post the outcome of my first attempted solution.

And for anybody wondering the orifice uses a 10mm wrench.
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Old 07-13-2011, 08:38 AM   #10
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Still Scratching My Head

I removed the orifice and soaked it in isopropyl alcohol overnight (and taped off the opening so no critters could crawl in the large hole left by removing the orifice). I also removed and reconnected all the spade connectors on the board to make sure they had fresh metal to metal connections. I used the compressor to gently blow out the flu, and bought a dual propbe thermomoeter so I can monitor the freezer and refrigerator compartment temperatures without having to open the doors. I also mesaured the resistance on the thermistor while it was sitting in a glass of ice water and that proved OK (9300 ohms - it should be between 7000 - 10000 ohms).

On AC power and the eybrow panel temperature control set to "3" the freezer is steady at 0F and the refrigerator is steady at 36F - 40F.

On gas and and the eyebrow panel temperature control set to "3" the freezer is steady at 0F and the refrigerator goes up to 58F - 62F.

What I don't understand is how can the freezer be so cold and the refrigerator warms up?

I have it running on gas with the eyebrow panel temperature control set to "5" to see if that makes a difference in the refrigerator compartment. I will report back with my findings.
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Old 07-16-2011, 08:37 AM   #11
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Some Progress

Well the only thing left to do was to make sure that the regulator at the propane tanks was adjusted properly and producing 11" of water column at the appliances. So I bought an LP Manometer from Amazon for $33.00 (another tool for by collection). There are test ports on every appliance in my trailer except for the stove top burners but the were easily tested. The manometer comes with a NPT threaded barb fitting that fits the test ports.

I turned off the gas at the bottles and used a 3.16" allen wrench to remove the test port plug on the refrigerator and threaded in the barb fitting that came with the manometer. I then fit the hose to the barb fitting, turned on the gas and lit off the refrigerator. When I got back to the manometer it was only reading about 7" of water column. My next step was to remove the plastic dust cover on the regulator and then remove the large black plastic hex nut cover on the regulator to reveal the adjuster. I used another allen wrench and moved the adjuster in towards the diaphragm (clockwise rotation or tighten) in 1/2 turn increments until 11" of water column was achieved on the gauge. I then turned off the refrigerator, turned off the gas, put the plug back in the test port, turned the gas on, fired the refrigerator up again and used Windex to test for any leaks at the test port.

After the refrigerator I repeated the same process at the water heater and furnace. For the stove top burners I just used a hex wrench to remove the burner orifice, fir the rubber boot on the manometer tube over the opening, fired up another burner and turned on the test burner. All appliances now show 11" of water column so we are all up to spec.
I left the refrigerator on gas overnight with the access door propped wide open and this morning with the eyebrow control set to "5" the freezer reads -10F and the refrigerator compartment reads a steady 41F. So hopefully my problem is licked. I am still going to have the RV dealership test the electronics boards to make sure that part of the operation is up to snuff.

I might also invest in the cooling fans that everybody talks about to get better air circulation going up to the vent. I also took notice that in my '06 Airstream did create a baffle out of luann plywood to reduce the amount of space behind the refrigerator plumbing.

I have included some close up pictures of the test ports on each appliance and the orifice that I removed on the stove burner.

Now that I know more than I ever wanted to know about ammonia absorption refrigeration maybe I can get a job at the local RV dealer

Definition of a specialist: Somebody that knows more and more about less and less.

The pinnacle of specialization: Somebody who knows everything about nothing.
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Old 07-16-2011, 08:54 AM   #12
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carl, thanks for this post. since you're an expert now ;-) would you happen to know if a gauge can be permanently mounted in the test port? i see the new trailers don't have one like the excellas once did.
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Old 07-16-2011, 09:07 AM   #13
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Carl,

Very interesting, thanks for the info. Kinda points out basic stuff counts big time.

Where did you get the thermometer?

Gary
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Old 07-16-2011, 09:37 AM   #14
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Quote:
Originally Posted by richinny View Post
carl, thanks for this post. since you're an expert now ;-) would you happen to know if a gauge can be permanently mounted in the test port? i see the new trailers don't have one like the excellas once did.
Rick,
I guess a manometer would be able to be hooked up, but I would imagine it should be hooked up right after the regulator at the bottles. Otherwise you would have to one at each appliance. Plus I don't know how the gauge would hold up to the rigors of travel. It would also have to use pipe/hose/tubing a little more stout than what came with the test gauge

I think it would siffice to test the pressure and adjust the regulator as necessary once a year. I know I will be adding it to my de-winterization checklist

Where is there an LP pressure gauge on the old Excellas??? We have an '87 34' Excella 1000 and we don't have one.

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Carl,

Very interesting, thanks for the info. Kinda points out basic stuff counts big time.

Where did you get the thermometer?

Gary
Gary,
I got it off of Amazon too. I just did a search for "dual probe thermometer" and the one I got seemed to have the best features and reliability.

If you are going to use something like this to monitor the refrigerator be sure to put the probe in a class of liquid. For the freezer I used a glass of cheap vodka and plain old water for the refrigerator probe.

This is the link to the dual probe thermometer on Amazon. It was $25.00 and I'll be able to use it when I fire up the BBQ.
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