Dometic 2201 Temperature Performance. - Fiberglass RV


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Old 02-12-2010, 01:29 PM   #1
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I have a 1984 (ish) Dometic 2201. The fridge is out of the trailer as I had to repair both LP and DC functionality.

All is working now.

What I am finding is what everyone else says - AC and LP work the best.

But even AC and LP only give me an approximate 45F degree temp drop over ambient (even at max cooling setting).

This might be a problem here in Florida in the summer as daily temps are well over 90. Max safe food storage temp (raw meat) is 40 F.

Is this performance similar to what others have seen??
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Old 02-12-2010, 04:44 PM   #2
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This is a question best answered by the master, Harry Young.

But let me toss these considerations into the conversation:

1) Insulating the enclosure within which your refer resides (especially with some foil-backed material) will help keep both ambient and radiant heat from affecting the "inside" performance of your refer.

2) Adding a small 12v exhaust fan (or two!) to the rear of your refer will help airflow and allow your heat exchange components to perform more efficiently.
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Old 02-16-2010, 02:38 PM   #3
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What Robert said. Insulating the fridge is critical, as is getting as much hot air as possible out of the enclosure. You can buy the small CPU fans at radio shack for about $3 ea and mount them at the top of the fridge cabinet against the outside vents to keep it cool. I have mine wired to a switch and a plug located just inside the lower vent door so I can turn the fans on when I am driving or not in direct sunlight. When I'm stationary, I plug in a small solar panel and throw it up on the roof to keep the fans spinning without using any battery juice.

You may also want to consider building a shroud out of thin metal (ductwork) to go from the the sides and the top of the fridge towards the edges of the cabinet to also help direct the hot air away from the back of the enclosure.

These mods alone will probably double your unit's efficiency. P.S. always make sure you're parked on level ground when the fridge is turned on.
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Old 02-16-2010, 10:48 PM   #4
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Oliver, Angelo,

If I use low volt fans (.25 amp) to move more heat out of the condenser area (outside coils) and insulate by one additional inch of urethane foam (reflective foam at home depot) and reflect infrared energy, (silver foil) I can maintain a properly charged refrigerator with less than 1/4 inch of ice on the evaporator (inside freezer) to 34 degrees at less than 25% humidity at 100 degrees ambient outside temperature.

Heat in and out of an absorption system is an elegant equation, we do not make cold in these machines, we transfer heat energy out of the food space, ergo we minus the equation on the inside of the refrigerator by increasing the amount of heat moved on the outside of it.

(I am deliberately avoiding the explanation of the absorption cycle because its a variable of design the operator is stuck with)

The insulation added retards the penetration of heat energy thru the wall to the inside, and the reflective barriers reflects energy that would penetrate thru the insulation and raise the temp of the food inside.

If you ever drove in a well air conditioned car, and rested your arm on the closed un-tinted window ledge you will know what I am talking about...You must move the arm soon because regardless of the inside temp being cold the arm is hot...Not the air around it...Just the arm.

Food lockers behave the same way, the contents can get warm, then that warms the air in the cold box...There are other sources of heat regarding food such as chemical energy, or humidity that retards efficiency, also behaviors of sugars, and how frequent you access the refrigerator too, how thick the ice layer is in the freezer, the thicker the ice the poorer the performance of the evaporator...Finally re-penetration of removed energy, an issue in trailer design.

Want to survive in the Arctic? Build a snow house, its -50 outside and +30 inside the snow shelter...Your refrigerator is exactly the same, keep the ice thin in the freezer/evaporator.

I keep ice cream in mine, and its an old one too, I included in the design of the built in cabinet space different technologies to enhance the refrigerator operating universe.

First think of putting a heater in a tiny closet, put a tiny door in the bottom and a small vent in the top...How hot does it get? Would you place your typical food Styrofoam box in that location? Yet its exactly what we do in our refrigerators even today.

The heat in this space can re-penetrate the cold box after we worked so hard to get it out?

With fiberglass trailers of yesteryear in particular we must realize that they are semi clear plastic lenses, the color we see is a several trash bag thick color pigment on the surface. This pigment is in no way formulated to block U.V.A or B light, let alone will it even phase infra red energy (insensible heat) insensible heat is by definition heat that cannot be managed thru a mechanical process. Insensible heat must be handled practically two ways...

(1) Don't be there when its there.
(2) Reflect it away.

Insulation delays penetration of this energy BUT is not as effective as reflecting it is.

The reason the 12v functions on 3 way refrigerators are not as effective is the input watts on a 12v heating element are substantially lower, whereas the input b.t.u.s (measure of heat) in the burning of a propane flame is as high or higher than the 115v element.

Design is not really a thing as owners we have allot to say about after a purchase is made...But we can increase the heat out of that tiny space the refrigerator is encased in, limit the available heat to re-penetrate our refrigerator from that space, super insulate the outside of the refrigerator, and line the space with a highly reflective barrier to send away energy the machine cannot trap or handle. (insensible infrared heat specifically)

Hope this helps, I try to keep the explanations to a non technical level in a real world sense.

Some promising things are coming in this technology, its exciting to read the research trade zines, the new Danfoss line of compressors solve the losses in power conversions 12v to 115v but are still primitive in still being stubbornly mechanically typical. (reciprocation piston design) I predict a screw or rotary takeover soon which should make the next leap in refrigerant base compression technologies for R.V.s... Next ultra sonic refrigeration will come out of nowhere possibly. Perhaps years farther out the nano tech researchers will trump these techs by the end of my career.

Until then the ammonia absorption system is my best friend.

Happy Camping, Safe Trails.
Harry
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Old 02-16-2010, 11:23 PM   #5
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Good golly, I told you Harry was the MAN!
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Old 06-01-2010, 11:43 AM   #6
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I have finally managed to get to the end of my restoration and the Dometic is in place.

I saw what I consider as poor performance of the fridge when I was testing out on my covered deck. As mentioned earlier only a 45 degree f delta T from inside to outside.

As I am in a time crunch the only thing I managed not to do is add the fans to move more air.

What I have done is as follows.

1. 1.5" of foil backed insulation on both sides and top of unit.
2. Confirmed door seal is good (both visual and dollar bill test).
3. confirmed door alignment is good.
4. Added "turning vane" at top of fridge as recomemded in Dometic manual.
5. Added sheetmetal baffle at top coil to direct airflow over coil (as recommended in Dometic Manual).
6. DC heater power usage in spec.
7. AC heater poer usage in spec.
8. LP delta T performance matches AC performance.

I have logged the temperature performance over a 24 hour period and again I am disappointed with what I have found. Still only 45 def F delta T. Basically all of the steps outlined above have had no effect.

I am going to add some fans to see if I get drastically better performance but as it stands right now I am going to need at least 25% increase in performance to get to the "raw meat" cooling level. I am doubtful.

Could I be looking at a bad cooling unit?

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Old 08-02-2010, 07:31 PM   #7
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Originally Posted by Oliver P View Post
I have finally managed to get to the end of my restoration and the Dometic is in place.

I saw what I consider as poor performance of the fridge when I was testing out on my covered deck. As mentioned earlier only a 45 degree f delta T from inside to outside.

As I am in a time crunch the only thing I managed not to do is add the fans to move more air.

What I have done is as follows.

1. 1.5" of foil backed insulation on both sides and top of unit.
2. Confirmed door seal is good (both visual and dollar bill test).
3. confirmed door alignment is good.
4. Added "turning vane" at top of fridge as recomemded in Dometic manual.
5. Added sheetmetal baffle at top coil to direct airflow over coil (as recommended in Dometic Manual).
6. DC heater power usage in spec.
7. AC heater poer usage in spec.
8. LP delta T performance matches AC performance.

I have logged the temperature performance over a 24 hour period and again I am disappointed with what I have found. Still only 45 def F delta T. Basically all of the steps outlined above have had no effect.

I am going to add some fans to see if I get drastically better performance but as it stands right now I am going to need at least 25% increase in performance to get to the "raw meat" cooling level. I am doubtful.

Could I be looking at a bad cooling unit?
Hi, Ian here, what is the age of the fridge? I have used numerous Dometic fridges and had no problems even in the heat of Death Valley. I do my best to park the trailer so the fridge is on the shady side in the afternoon but even that has not really been necessary. Propane is always the best way to test cooling as it is the best heat source. On one old fridge I had, after sitting over the winter it would not cool very well. I simply took the unit for a good drive over hills and round curves. This tends to circulate the cooling fluid.

Let me know how you make out.

Sincerely, Ian
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Old 08-02-2010, 09:33 PM   #8
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Wish I was so lucky. Spent a week learning refrigeration on the fly so I could trouble shoot why my Dometic 2200a (circa 1986) stopped making cold air a few weeks ago. Plugging into AC produced heat but not to the inside. Running off propane did the same. Call to Dometic revealed they no longer stock ANY parts for this old-timer and could offer no work-arounds when I wanted a new propane thermostat, (leaving me to solve that problem myself).

It all boiled down in the end to needing a new coil, a $300 item at antique parts suppliers. Yah --- when pigs fly, I told 'em! Back to ice.
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Old 08-03-2010, 06:11 PM   #9
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You can also purchase from Camping world a small battery operated fridge fan that works for me. Had mine running for well over 10 days and it kept going no battery change - simple.
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Old 08-08-2010, 12:34 PM   #10
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Have you tried removing your fridge and turning it upside down for a few hours? That is a fix that has helped innumerable campers with these types of units. Apparently the refrigerant gets bubbles in it or something and stops working. I had a family member take his fridge to an rv dealer, whom he was friends with and the fellow pulled it out, turned it upside down and said "lets go visit for an hour". After chatting for a bit he righted the unit and put it back in the camper. It worked as good as new. The fellow said those Dometic fridges and others like it last almost forever. I believe its the same reason that Ian, above, found "I simply took the unit for a good drive over hills and round curves. This tends to circulate the cooling fluid." . Anyway, it works a lot of the time and doesn't cost anything, so why not give it a try?
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