My Absorption Fridge RMD 8551 Class ST

Submitted: Monday, Jan 27, 2014 at 15:25
ThreadID: 105974 Views:7891 Replies:3 FollowUps:5
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Rather than continuing a thread hijack I will pose my question here.

Partly discussed with PeterQ my fridge when the van was delivered new 6 weeks or so ago was to my mind not well installed. I voiced my thoughts to the manufacturer who stated that ......."this is how we always fit 3 Ways and Dometic have signed off on it as being correct."

They have though agreed to fill the air gaps around the cabinet by their service agent and a 'baffle' fitted to try to steer the air out the top vent. This has been done but the fridge still does not perform anywhere near like it should.

The van is currently at the local Dometic Agent to check if there is actually a fault in the fridge. When turned to Max setting over a coolish night it will get to 1°c which is fine but when I cut back to setting 3 (of 5) the temp climbs to 7 - 10°c. On gas it is worse.

My problem, the bottom of the top vent, (which is the later style large vent with separate chimney flue outlet,) is well below the top of the fridge cabinet. This is due to the Microwave being fitted above the fridge and not allowing the vent to go higher.
Should I block off the lower portion of this vent so to make the top of my blocker level with the top of the cabinet to prevent air 'falling' out the vent before it has completed it's pass through the fins? This of course will make that lovely big vent only half the size.

I was also very disappointed at how the trim on the van interion around the fridge was finished, you could see daylight around it via the outer vents. To my mind this borders on illegal as it would allow oxygen to be drawn to the combustion area from the van or allow burnt gas to enter the van. This was rectified by the agent.

When Dometic do what they can with it I will fit an exhaust fan to the top vent via a thermostat if still necessary.

Thanks for looking
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Reply By: Ross M - Monday, Jan 27, 2014 at 17:39

Monday, Jan 27, 2014 at 17:39
G'day Neil
Just my idea, but the fridge is designed to be cooled by convection flows.
If it is free standing in the there much of the convection is eliminated.
If you use a thin plate of aluminium at the rear of the fridge and close to the recirculation tubes ( large black ones on angle) as possible At a guess 300 wide and 300 high. It will create it's own column effect for the rising heat to have a sort of chimney to flow up.
Since heat rises, the flow will draw cool from the adequate bottom vent and aid cooling rates.

If you also have a small computer fan "Quiet essential" it can blow air upwards through that gap and vastly increase cooling of the condenser as it aids convection flows.

Often a large flow isn't required and two computer fans wired in series with one at the bottom and one at the top to drive out hot air mass will give a decent change of air through the system. The two fans in series can be run off, either a 240v plug pack "Small 200ma at 12v is enough", or with a simple changeover switch, the vans 12v system and can run full time in hot weather.

Two fans in series runs slower/quieter but still effective and last long "time no see".
Caravan crowds don't often seem to apply themselves to this recurrent problem.

Ross M
AnswerID: 525228

Follow Up By: Keir & Marg - Monday, Jan 27, 2014 at 18:51

Monday, Jan 27, 2014 at 18:51
The Dometic in our 2003 Jayco Penguin works very well, but the cooling unit was replaced by the first owner whilst on a trip to the NT, and I suspect we have a Tropical-rated unit. On gas or 240V, it certainly makes ice in the freezer compartment even on a 35C day, and freezes lettuce in the fridge section if the lettuce is anywhere near the cooling fins. I've just added some cardboard as per Ross M's suggestion, horizontally at the bottom of the recirculation tube fins to assist in the chimney effect, and will see if that makes it even better. Haven't gone the computer fans route yet, but now we have a solar panel, LED lights and an excess of power, that may be the next step.
Please let us know the results of Dometic's efforts to improve the performance of your unit.
FollowupID: 807122

Reply By: oldtrack123 - Monday, Jan 27, 2014 at 22:45

Monday, Jan 27, 2014 at 22:45
HI Neil

[1]Both pics seem to indicate quite a large space each side & o top of the FRIDGE
ALL BAD place for hot air to accumulate & massive cooling air loss by passing the condenser ,even withe a fan on the grills
ON top,
force some styrofoam sheeting into the top gap to completely fill it if you can THAT will also ADD extra insulation
ON the sides,
the picture is a bit decieiving as it appears The cabinet inclosure sides are angled but I suspect they are parallel to the fridge sides??
Again pack as much Styrofoam sheeting as you can in that space,making sure that they are in contact with the FRIDGE sides
IF it as wide as I suspect THAT will realy add some insulation& reduce losses

ITdoes appear that the fridge rear is pretty close to the van side wall can you measure THAT clearance at the closest point??

The actual location of the top vent does not look too bad
If there is an air gap between the chip board & theTOP section of the vent grill vent, it would not be a probem , IF you fit fans at the bottom of the condensor

I cannot see the actual boiler, exhaust flu etc?
Does it have a direct connect to the outside via the top grill
Please post pic if you can of that section LOOKING DOWN INTO IT& the top grill itself
IT may be advisable to fir some horizontal baffles
From what I can see,MY recommendation would b
Again to ENSURE as little as possible HOT air is recirculatede to make a small wooden frame
say 50mm deep, the length & width of the condenser

If necessary slot it to fit over piping
Attach two or three Small computer or similar type 12V fans to the under side of the wooden frame
Fit the WHOLE lot as close as you can to the UNDERSIDE of the CONDENSER
Connect ALL the fans in parallel to the FRidge 12Vsupply via a thermostat JAYCAR part #ST3831 Fitted directly to the top of the condensor fins about MIDWAYalong with say a 5Afuse fuse in the pos linewhere you take it off from the FRIDGE 12V SUPPLY terminals
I cannot see any problem with the bottom vent
Except the wiring mess
Could you let me KNOW what the marking are on those terminal blocks???AS I havenot seen the rear of that model !!!

That INSTALL well & truely FAILED to meet the GAS regs
It is Frightening what some /most van makers do!!!

Come back if necessary AT ANY TIME

AnswerID: 525240

Follow Up By: landseka - Tuesday, Jan 28, 2014 at 00:45

Tuesday, Jan 28, 2014 at 00:45
Thanks Peter,
I don't have the van at home at the moment as Dometic are still looking at it. Here is the original pic which I hope you can see the details of connectors.

The cavity sides are parallel to the fridge and have been packed with insulation material as well as above the cabinet.

The rear of the fridge is, to my mind too far from the van side also. From memory it could be at least 80mm closer if the copper gas pipe were modified. When I get the van back I plan to pack blocks of polystyrene foam to almost fill that gap. I will also try to get a pic looking down from the top vent.

The exhaust flue exits the van via a separate outlet which is different to the usual (older) style. I will get a pic when I get the van back.

I don't know if you are aware but Dometic now actually fit a fan below the cooling fins as standard which, via a thermostat blows upward to help expel hot air.

Thanks also Ross & Keir, I will let you know how it progresses.

Cheers Neil
FollowupID: 807132

Follow Up By: landseka - Tuesday, Jan 28, 2014 at 00:47

Tuesday, Jan 28, 2014 at 00:47
Hmmm, pic was no better than the last one. Could you email me Peter on neil2 at internode dot on dot net Thanks
FollowupID: 807133

Follow Up By: oldtrack123 - Tuesday, Jan 28, 2014 at 22:09

Tuesday, Jan 28, 2014 at 22:09
HI Neil

80mm is far to much space the current
You should try to fit a full width horisontal baffle level with or just below the condenser fins
Again with the idea of ALL the cooling air IS being drawn through the condenser fins by NATURAL draft as much as possible
But you foam blocks could do the same thing
The boiler exhaust Flue is OK, that is what I hoped for!!
Yes I believe I made reference to that in an earlir post
IT has only taken them something like 40+ years to see its advantage & offer that option
BUt ONE van without good baffling will not do much good
IT will ,to a large extent, recirculate hot air

I did that with my first van's absoption ELECTROLUX fridge way back in the late 50S early 60S

IT was a common practise with absorption fridges, when they became very popular post WW2 ,[old Silient Knight C.Hope's "Cold Flame' etc]all improved when air was forced over the condensor


But GOOD Condenser cooling was recognised looong before that

A OLD coalmining ghost town in FAR Nth Qld,had several large semi coimmercial absorption frigdes laying around that had the condensors immersed in tanks of water which were tricle feed.
That town closed down in 1928!!

ps even with te NEW unit it will pay you to consider ALL the suggested mods
FollowupID: 807213

Reply By: landseka - Tuesday, Jan 28, 2014 at 13:34

Tuesday, Jan 28, 2014 at 13:34
I just spoke with the Repair Centre and have been told they are going to fit a new Cooling Unit which should be delivered to them tomorrow.

I await with bated breath.
AnswerID: 525268

Follow Up By: landseka - Tuesday, Jan 28, 2014 at 22:19

Tuesday, Jan 28, 2014 at 22:19
I suspect this new Cooling Unit will not be the problem. The fact that it DOES cool at all indicates that.
There are no moving parts in the Cooler so it should either work or not. I am more inclined to believe the problem lies in the Control Unit. Thermostat perhaps. We will see.
I watched this clip This link and learnt more that I have from all the forums I have read. This is Part 1. The rest are worth watching too.
Cheers Neil
FollowupID: 807214

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