Fridge - Venting 3way absorption fridge

[keelz]

ok after much kickin' and naggin' LOL here is a separate thread to kick off discussion and share the good and bad about improving ventilation and operation of the absorption type fridges found in our classic 70's vans.

Bear in mind that a lot of our older fridgers are only N or SN rated and can really only manage 25 degrees below ambient. With some basic venting improvements you can improve performance of the fridge during warmer weather. Unless you have a 'T' rated newer model fridge (Rated for up to 43deg ambient), chances are you will find the results of a digital thermometer or data logger very interesting if you check out your fridge on a hot day.

Note: If taking measurements, make sure you place the probe in a cup of cool water and let the fridge cool that water for a few hours and the measurement of the actual temp will be much more stable compared to air temp measurements inside the cabinet which fluctuate as you open and close the fridge!

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Currently the existing louvres in the van wall and removable panel have just not been allowing enough airflow, it comes down to cross sectional area/open airflow and these things were just not cutting it to allow the fridge to breath adequately. The top vent was also badly configured from the time the van was built, sealed off with flymesh full of dust, etc. On a hot day the fridge has been suffering as a result and performance hampered.

After having the fridge re-built earlier this year i have fitted 12 volt fans on the back of the fridge that are switched via a thermostat on the coils as the weather warms up and the fridge cranks up the heat to keep up, they automatically kick in, or I can manually overide.

Next had to improve the venting to create a better draught behind the fridge.

In with the new Dometic vents. I always hate having to cut more holes in the van walls and this was a tricky location to make watertight but I think the end result and improved fridge performance will be worth it. Pic with the upper vent now in, I couldn't decide on using the 4 inch grinder, the jigsaw or my recipro saw for this job. I ended up running with the 4inch with a fine/narrow aluminium cutting blade. Worked a charm with 4 rounded holes in each corner done by the drill bit. This allowed me to cut the outside face first without trying to have a large blade punching in and out of the wall cavity and hitting inside panelling with the other two options........



This vent is taller above the top of the fridge and required modification of the venting setup internally so i can install a metal heat shield under the existing plastic splay duct.

So i started knocking it up


test fit and view of the vent internally, much bigger opening than the old setup. The original setup had a small rectangular cut-out in the timber panelling, to allow the hot air to vent up the wall cavity and out the louvres. Problem was the hot air was getting trapped inside the wall cavity and just wasn't escaping.... This new top vent also has allowed me to fabricate a new flue extension to the top of the gas flue exhaust pipe, now fully ducted externally via the vent kit and t-piece section. Less heat in the cabinet area, more heat going outside


another test fit - with the old plastic duct on top.


side view - much higher now due to increased wall opening height.


running much cooler now with a test run for a cpl of hours with things sitting loosely in position


after a couple of simulated sundown 'beer runs' - door opens door shuts.... is now pulling better temps, have also put the fridgemate battery fan inside for a test run - it seems to help the cabinet temperature pull back down to temp a lot faster by helping with a bit of air movement, so that little fan is coming on our next trip


the fridgemate running internally



Finally i am starting to get some nice frosty fins with it cranking a few deg's cooler just wait till i get this thing loaded up lotsa cold stuff


Get onto Google and start looking up three way fridges, venting, 12volt fans, etc. There is hundreds of pages of information useful for assisting.

Here are some starter references for the venting requirements.

www.caravanandmotorhomebooks.com/articles/fridges_two.htm

www.fridge-and-solar.net/fridge_vent.htm

www.rvmobile.com

The original vent design of the Viscount setup was a good attempt, but after doing some reading i came to the conclusion that it was less than satisfactory to get the best results out of the fridge.

I also came across a website with all the Dometic manuals for all the fridge models, very handy if you have bought an old classic without any manuals....Yee haa

www.dometicmanuals.com:8080/dometic/masterdometic.nsf?Opendatabase

At present i have two 12volt fans located on the back. I'm experimenting with the use of 1 and 2 fans individual and combined, with slightly different fan capacities. The thermostat is a 12volt normally open thermostat switch.


When the middle coils on rear of fridge heat up over about 70 deg the fans come on automatically. I have a bypass wire fitted to the switch on top of the fridge near the vent that allows me to override and switch the fans on earlier if we are expecting a stinkin' hot day. The fans at the back have resulted in reducing the fridge temp on average by about 3-4 degrees on an normal day. It is amazing how much just a bit of airflow up behind the fridge helps. I used to hold my hand near the old ally wall vents and didn't feel much air movement (even with the fan fitted).
Now i hold my hand in front of the top Dometic vent and can feel a steady flow of warm air

the vent kit came from caravansplus with the couple of extension pieces as shown on their site. Due to the height of my fridge, the black extension pieces were too short and their diameter was too small for the existing flue discharge diameter on the fridge. I have used the top aluminium piece and the metal t-section that came with the kit. The fridge used to have an aluminium flue with a small vent hole in the top. I removed this and scrounged around the garage. I found a length of old Electrolux vacuum cleaner aluminium hose pipe in matching diameter and wall thickness! Perfect - I chopped a section down and have very crudely connected it together for now.

The heat that comes out the top plastic vent dissipates pretty well, the passing breeze external helps remove the exhaust gases quickly. The plastic is the same stuff that the gas hot water heater louvre is made out of, it seems to cope ok. The only downside is that after test running the gas i reckon that i got a couple of flame-outs.....but this only happened once during extremely windy weather. The best thing is it's helping to get rid of the nasties outside into the atmosphere, not sitting inside your van.

Here is the fan arrangment with the rear linings/baffle covers removed....the fans you need are the ones out of the old computer power supplies. Find some old computers and strip the fans out of the power supplies. Usually they have 2-3 wires, just go for the red and black. I've found that one fan is satisfactory. I've got two because one is wired full time to the tow vehicle 12v feed to the 12v element on the fridge and the second fan is just wired to a plug pack transformer that i've got in the cupboard under the sink.

Use a bit of 25 x 25 aluminium angle, notch out a section for the fan's airflow path, drill a few screw holes and there you go!

The small fans from the motherboard chips might be a bit small to get the required air movement. I reckon they would be ideal however to use inside the fridge cabinet to circulate cool air. Some of those smaller fans might run off 3v? or so.

I've seen some guys who also use a power supply fan inside the fridge cabinet and just run it off the same 12v circuit by sneaking some wires into the cabinet through the holes that the thermostat wires feed through into the cabinet instead of purchasing/using a Fridgemate fan...



New matching lower vent (old louvre sections blanked off to help create draft path starting down low at bottom vent, up over absorber, coils and top coiling fins and out through top vent)


Then back inside the van. Fabricating new heat deflector out of sheety ally to fit the new upper vent box/enclosure.


test fit with plastic cover back on top for aesthetics and it has foam gasket strips installed all over it to seal out air and insect movement into van.

The movement of hot air out the top vent is much more noticeable now since the installation of the new vent kit, i could never feel much air movement coming out of the old louvres due to the bad flow path inside the cavity wall.

Ok this is just a starting point and may assist others reviewing the venting of their fridges. Feel free to add to this and hope it helps others.

Cheers

Keelz

[Deleted]

Hi Keelz,
good post . ;D ;D the old (and a lot of the new) vans had terrible fridge ventilation. What between improper design and just poor installation, they never worked well in hotter temperatures. no sense chucking out a good fridge when all you need is better ventilation.
You have shown how to do the improvements in a step by step fashion, this should help others who are not so sure.

Frankidownunder.

[Deleted]

Thanks Keelz. I sure couldn't find it

Here is an excellent article which explains why running the fridge via 12 volts from the car battery/ alternator is fraught with very real performance issues.

It also clearly explains why a van mounted battery cannot be satisfactorily charged from the cars charge system.

And the solution ..... that we have discussed elsewhere started by Mike.



There are however safety issues with this solution and a means of protecting against electrocution from the output of the inverter should be installed. More to come here.

[Deleted]

Here's Ray's most excellent info on fridge problems.

Seems to have hit all the key points.

Here is the snap of the ventilation article. I've circled a couple of what I believe are key issues, likely left unattended during build.



And I love this pic of how an absorption fridge works

[Deleted]

I dragged the old 1978 York van out the other day for it's annual clean up, and it's once a year migration to the beach for a week or two (it's also rego time

The Tuomatic 2-way (240v/gas) fridge has never been the coolest, so I thought I'd better apply some of the awesome stuff you guys have been getting up to.

The final pic shows how the external vents relationship with the cooling coils.



I guess the next job is to:

But then ..... I mite just 'go to the beach'

[millard1399]

Keelz, I need a bit of guidance about the fridge in my Millard. The photos below show the position and layout of the fridge...



There is a gap above the fridge in the framework (photo bottom right) at the back of the kitchen cutlery drawer. There is about 4 inches distance from the framework to the back of the drawer, and a sloping canopy/deflector could be fitted in this space. Also, note in the bottom left photo that the fridge side as well as the rear fridge space is open to the kitchen cupboards.

So now some questions...
1. Are the Dometic vent covers available in a size that would suit the frame opening above the fridge? (2^1/2 inches by 18 inches)
2. Is the fact that the fridge is open to the kitchen cupboards going to help with air circulation? The water/drain hoses go through holes in the floor and the holes are slightly larger diameter than the hoses, so air can get into the cupboards/fridge via that means as well. Based on this info, how many additional fans would I need to have at the back of the fridge?

Thanks for any help.
cheers,
Al.

[keelz]

Gday Al,

Ok after having a squizz at those pics you have posted.

Lets start with the gaps - ok, all those gaps need to be sealed off. So yep a heat deflector shroud from the top of the fridge at the back up to the top of a vent/louvre panel would be ideal. You need to get the top of the cavity area behind the fridge sealed up well so, for example if there is a gap or dead air space above the fridge below the benchtop it is really important to seal this off to prevent the hot air being trapped and hampering the efforts of both the cooling unit and secondly the fridge cabinet temperature - bearing in mind the insulation in these older fridges isn't fantastic.

The gaps at the side of the fridge also need to be sealed off. In the cupboard (and the other side of the fridge) you will need to seal off the gap between the rear side face/corner of the fridge running back to the internal wall lining of your van or otherwise. Something light and can be folded like some tin or aluminium or otherwise ply panelling. I already had decorative plywood side panels beside the fridge because it was stand-alone, added some alumium angles and put some gasket stripping where it sits against the wall. In your case, access is a little trickier with cupboards, etc.

I wouldn't have the space behind the fridge opening into the internal van living area or cupboards, so i would also close off that end of the cupboard or seal between back of fridge to the van wall lining. If you decide to line/close off the end of the cupboard, consider installing some polystyrene insulation between the side of the fridge and any timber panelling you may install for some added insulation to help the fridge.

Also a good excuse for sealing off the rear of the fridge is if you decide to run the unit on gas while camping etc it will help minimise the exhaust fumes from the gas flue working their way through your van while you're sleeping, etc. The more that goes up and out through the top vent into the external atmosphere the better.

Now the questions!

1. The dometic vent has a mounting frame with cut-out dimensions in the wall of 451mm W x 156mm H. I'm a child of the metric age so bear with me here....Google says in inches they are roughly 17.76 inches x 6.14 inches. So you definately have the width capabilities for both vents. Assuming you can't remove that lower frame member at the top?

What you could do is install the vent as high as possible under the top timber frame member where you have taken the measurements. The lower member at the top will partially obstruct the vent, however we aren't talking major mm2 area loss behind the vent. From memory the depth of the mounting frame suits wall thickness around the 25-30mm mark. You may find that once the vent frame is cut into the aluminium cladding the back edge of the mounting frame may either rub on it and require some shaving or notching or it may not touch it at all. (It appears to be recessed/set-back from the remainder of the frames in the photos?) I can pull a louvre out on my van and take a measurement of depth for you if you want prior to committing to purchasing the vent kit.

Ideally the bottom of the top vent should start at the top of your fridge, however you are lucky because your top cooling fins are set down from the top of the fridge a fair deal, which should assist if you are limited by the vertical position of the frame members.

2. No. I would seal off as mentioned above. Fan wise - i would start with one fan. If you want something quieter, use a 24v volt fan as it will run slower and quieter on 12volts although it's airflow will be a bit less powerful. If you can find an old computer, rip a 12v one out of the power supply box. Mounting options for fan - some people install the fan behind the top vent louvre using cable ties to help exhaust the hot air. Some install a fan down low near the floor blowing up. The guys who re-built my fridge installed between the absorber coils and the cooling fins (ie in the middle on the back of the fridge). There is no hard and fast rule.

Now - I do recommend before you do anything - have you bench tested the fridge to make sure it's running ok before you start cutting vents in , etc? If it runs ok in the van at the moment and you have the van levelled up, proceed further! ;D

Other thing i forgot to mention is check what's currently in your aluminium cladding wall for this area - did you have a removable louvred panel or similar? If you do decide to install the dometic vent kits and there is other louvres on the removable panel you can blank them off.

The main focus is to get the bottom vent in as low as possible and maximise natural process of hot air rising, the sealed off cavity behind the fridge will naturally assist the intake of cooler air through the bottom vent as the hot air rises and passes out through the top vent. Have a look at that diagram Wahroonga posted above and also some of those websites re: sealing off the cavity space.

Came back to add this - oopps nearly forgot. You may need to think about a baffle panel or bit of ply panelling before you re-install the external louvre section to the outside wall. Check out those websites for some guidance. Try and make sure you don't have a massive gap betwen the the rear face of the absorber coils and the cooling fins to the wall lining of your van internally. All you need is a small gap under say 10mm. Too large a gap and all the cooling air won't get pushed through the coils effectively and will go around it, particularly the top cooling fins. So may need some extra sections of timber or panelling to close up the gaps, they refer to them as 'baffles' on some of those websites.

Hope this helps!

Cheers

Keelz

[Deleted]

I can't add anything to Keelz's excellent advice.

And I would have a go at the baffle.

The original installation IS a long way from perfect; so anything that you do, will be better than brand new.

Perhaps simply stuffing insulation wool around the sides may do the job? Any thoughts Keelz? The top will need special treatment and a 'flu'.

[keelz]

Yeah insulation such as fibreglass wool or polyester could be stuffed into the top and around the sides of the fridge, however i would still consider some panels in colorbond, tin/galv sheet or aluminium sheet towards the rear where the gap/cavity behind the fridge. Polystyrene sheet foam would also be another good idea.

Reason is need to exercise some caution with what we shove at the back because of its close proximity to the flame in the burner section down low at the base of the cooling unit. Wouldn't want insulation getting dislodged and drifting into the burner when running on LPG and catching alight.

Then you could stuff in some insulation on the other side of the panelling if protected by kind of ideas mentioned above.

There are oodles of endless possibilities, but concur with Wahroonga that the existing ventilation does require some improvement.

Cheers

Keelz

[millard1399]

Yeah, but it's only a Millard!! What it really requires is a stick of dynamite! ;D ;D

...Two sticks to make d@mn sure!!

There's a late 70's model Viscount 14ft poptop listed on ebay at the moment, and showing as being from the same suburb as me. I'll ring the seller and pop around and have a squiz. Might be able to do a trade, eh? Could be a new thread in the Hall Of Fame section

cheers,
Al.

[keelz]

Stand clear T minus 5!

Nah c'mon mate its all good, you are gonna get a touchdown on that Millard soon

Viscount - yeah noticed it.... maybe it's the bushfires or something in the air or water, every man and his dog has his old 70's Viscount caravan up on ebay at the moment.....it's a classic vanners paradise.

it's hard to resist the lure of the classics i must admit. darn i wish i had a shed would have a fleet of the darn money shredders.

cheers

Keelz

[Deleted]

Feb 11, 2009 13:16:40 GMT 10 @wahroonga said:

I guess the next job is to:

But then ..... I mite just 'go to the beach'

Well I went to the beach, but got the side and top sealing done first.



The old Tuomatic has never worked so well.

[kylarama]

I highly recommend this to anyone.

I was about to bin my 34 year old 2 way Tuomatic in favour of a 240 volt only fridge. Decided to give this venting a try and what a difference. While it wasn't overly hot when we went away the fridge performed perfectly. Thermostat was set on just above 3/4's and had to turn it down to 1/2 and night to stop the milk freezing. Our friends that were camped with us have an 87 Windsor with a 4 year old Dometic fridge which was next to hopeless. First job for him when he gets home is proper venting.

How the fridge performs in 30 - 40 deg. heat over summer will be another story. By then I should have a 3volt fridgemate fan fitted and maybe some 12volt computer fans to assist the venting. We still travel with a 60 litre Evakool 12volt compressor fridge and a 70 litre fibreglass esky for drinks, so we're not dependant on it.

See her for some of my install pics.
ditzygypsy.proboards.com/index.cgi?board=photos&action=display&thread=520&page=8

[Deleted]

I have now got my Electrolux23 sitting in the shed working on gas, ,,had to fire it up manually,I could,nt get a spark so think the piezo is not working,

where could i get a new piezo,

next job will be to do the venting bit,as well as adding insulation to the sides and top and a fan to the freezer box,,as a matter of interest when i had IT running on 240V i removed the door from the freezer box and within a couple of days the coke frooze,,,,using a laser temp gun the fridge got to minus5 in the cabinet and held minus minus19 in the freezer box

[drylander]

well I'm quietly moving along with the van and I've started on the fridge. I packed foam insulation along both sides and the top and now working on the venting with no great drama (photos soon). The only question I have is in regard to the fans over the coils. If they blow downwards is that defeating the purpose of the upper vent to some degree or ar they sucking up.
Thats the bit that is confusing me.
Pete ( the confussed 1)

[ronaldjohn]

Pete,

You only require fans if the ventilation has not been fitted properly.

If you look at the first posting and pictures, Keelz has done the job perfectly.

The top vent must be above the fridge. The hot air rises and drags cool air with it, to cool the back of the fridge.

Cheers,
Ron

[kylarama]

As Ron said you won't need a fan if you get the ventilation right.

While the position of the top and bottom vents is very important, it won't work if you don't have baffles in place. You need to force the cool air through the coils.

Vented right and it will create a draught that feels like its fan forced. Our 35 year old fridge just spent the last 3 months running on 240v without a hitch, with a nice steady stream of hot air pouring out of the top vent.

[drylander]

thanks fellas now it gets harder I have the same set up as Millard 139898686545446etc ;D. Now I haven't got the vent system shown, mine is the standard vents the van came with but I am fitting the pipe from the top of the boiler to outside and as I have a comp fan I thought to fit that at the top to help to expel hot air. open to further suggestions
Pete
edit 1-6-11
Just checked the fridge and find there is only a 1.5 inch gap between the coils and the vent so the baffles prob would not be needed so it should be ok to block the vents to just leave a bottom and top section ala Kylarama but using some ali sheet in place of gaffer tape ;D (on the inside) as for the fan, well if I put it in aimed to blow air out of the top vent it is there to be used if needed comments please

[kylarama]

May 31, 2011 22:23:29 GMT 10 drylander said:

Just checked the fridge and find there is only a 1.5 inch gap between the coils and the vent so the baffles prob would not be needed so it should be ok to block the vents to just leave a bottom and top section ala Kylarama but using some ali sheet in place of gaffer tape ;D (on the inside) as for the fan, well if I put it in aimed to blow air out of the top vent it is there to be used if needed comments please

1.5 inches is too much, you want about 1/4 inch.
Read this link that was in the first post. Explains everything and show where the vents and baffles should be.
www.fridge-and-solar.net/fridge_vent.htm

Gaffer tape! I beg your pardon, I used '100 mile an hour tape', big difference ;D

[drylander]

so you did my humble appols ;D
so I have more work to do as I obviously can't read I see what you mean so now I have a handle on it. Hope I don't forget by the time I get to the van ;D
These senior moments can be annoying and at times amusing ;D
Pete