3 Way Fridges...and cooling theories....

Submitted: Monday, Jan 07, 2008 at 21:48

ThreadID: 53225 Views:4875 Replies:5 FollowUps:12

This Thread has been Archived

Member - Hughesy (NSW)

I was reading Collyn River's books on Motorhome / Caravan Electrics. He states (and it makes perfect sense) that between the bottom wall vent and the top wall vent for a (well in my case and his example) Dometic 3 way fridge you should have "baffles" in there so that the distance between the back wall and the back of the fridge is only 6-7mm. The logic is that the air MUST then pass over the fins.

In my Jayco there would have to be 4 to 5 inches between the rear wall and the back of the fridge (and the Dometic manual says a minimum of 25mm). Obviously its "easier" for the air to just go inside the vent and flow up the wall of the van and straight out the top vent.......with virtually no air movement over the fins.

Now, I've found an old 12v "computer" fan that I want to mount to aid in the air flow and hence cooling. I read the post the other day about "push" or "pull". I personally am for pull.

But the Jayco has another vent on the inside on the bench top, just above the wall mounted top vent. Therefore if you mount the fan on the top wall vent (pushing air outside) then the air will find it easier to pull down from the bench vent (less distance) and totally miss the fins. And if I mount the fan on the bench vent then the air will come straight thru from the upper wall vent - and double wammy because hot air is then blown into the camper which is far from ideal.

So my question is .......do I mount the fan onto the top wall vent and block the bench vent and also either side of the fan??? This ensures the air travels exactly where I want it.

Do I try and add some baffles so that it is similar to what Collyn was talking about in his book??

Do I go against the norm and mount the fan on the top wall vent (sucking from outside) and blowing roughly straight onto the fins...which are about opposite the vent and hope the turbulent air flow will be more effective???

Must be someone who's retired (Willem??) and has tried all these various options and some others????

I'm all ears.

PS. the reason this has come about is because it took about 36hrs for the fridge to get cold enough to put something in it. This was on a 40deg day (Broken Hill) and the bench top and sink top inside (above fridge) were that hot you could not leave you hand on them without severly burning them...... The top still gets that hot even on mild 30deg days.

Back Expand Un-Read 0 Moderator Share

Reply By: Member - Longtooth (SA) - Monday, Jan 07, 2008 at 22:25

Monday, Jan 07, 2008 at 22:25

Had this exact problem. Pulled the fridge out and placed baffles adjacent to the coils both top and bottom with a gap of 5mm between baffle and batten. Also filled all space around the fridge with insulation. Placed fan in between coils so that the fan sucked over the lower coils and blew over the top coils. Fitted a galvanised (handy material in shed) shield from top of back of fridge to top of upper vent. The shelf temperature inside is now hardly different to the rest of the bench tops - before was extremely hot to touch as you indicated. NOW - the fridge gets much colder at a much lower thermostat setting. The inside was 4 degrees at a thermostat setting of 3 on a Kelvinator 3 way fridge on 240V (fan on) 6 degrees (fan off) and 4 degrees at thermostat setting of 6 (fan on) on gas in the shed last week when the temperature of the shed was 45 inside. It's worth the time spent for little cost. Haven't tried it on 12V yet but added heavier wire to fridge and it was considerably cooler but the temperature was only 25 outside at the time.

AnswerID: 280381

Follow Up By: Member - Matthew C (WA) - Tuesday, Jan 08, 2008 at 00:29

Tuesday, Jan 08, 2008 at 00:29

When you say you filled it with insulation,what did you use exactly and did you fill ALL the gaps around the sides and top and leave the back clear for airflow?????

Mine has about 4-5 inches of clearance around the back so was thinking of leaving it like that just fittting some baffles to stop the air from circulating around the fridge and instead going over the coils.

MAtt

FollowupID: 544619

Follow Up By: Member - Hughesy (NSW) - Tuesday, Jan 08, 2008 at 05:53

Tuesday, Jan 08, 2008 at 05:53

Thanks Longtooth. Looks like the baffles and a bit of insulation might be the go.

FollowupID: 544627

Follow Up By: Member - Longtooth (SA) - Tuesday, Jan 08, 2008 at 22:03

Tuesday, Jan 08, 2008 at 22:03

For Matthew C and Hughesy,

Filled all gaps to the top and sides with polyester 3.5 batts or portions thereof. The back was left clear of insulation and only the baffles and fan placed in the back. Also had the director shield at the back from top of fridge to top of top external vent. Even with the fans off the air from the top vent now is quite hot and it never was before (probably because it was above and around the fridge keeping it hot).

FollowupID: 544756

Reply By: GerryP - Monday, Jan 07, 2008 at 22:34

Monday, Jan 07, 2008 at 22:34

Hi Hughsey,
I went through this exercise some 2 years ago and fitted the baffles as you have outlined. I also made a scoop near the top directing the air towards the top vent and mounted 2 x 12v computer fans to the top grille drawing air from below and blowing it straight out. I also insulated the cabinet and completely filled in the spaces on the sides and top with styrene. Unfortunately, none of this made a huge amount of difference.

However, some people claim to have had various levels of success, so you may be lucky. With regards to the fan placement in your case, the air flow MUST be made to flow towards the top, therefore, your suggestion of having the fan at the top, sucking from outside (i.e. blowing into the space behind the fridge) will not work. You can either block off the vent inside the van and have the fan drawing through the outside vent only, or put the fan behind the bottom vent and blow in from there, being careful not to blow the pilot light out.

What a friend of mine has done is to remove the freezer door inside the fridge. This has apparently made a huge difference. I heven't tried it, but perhaps a few holes in the freezer door, or an adjustable vent of some sort may even help - I really don't know, but I have been tempted to try it some time.

Personally, I feel that any temperature over 30 degrees outside and most absorption fridges seem to start struggling.

Cheers
Gerry

AnswerID: 280386

Follow Up By: Member - Hughesy (NSW) - Tuesday, Jan 08, 2008 at 05:58

Tuesday, Jan 08, 2008 at 05:58

Thanks Gerry. Seems there is many options for the location of the fan.

Your right about the freezer though. It gets cold very quickly, but the cooling of the fridge compartment takes forever. I'll have a look on the weekend at how easy it is to remove the freezer door.

I'm in the process of running some nice heavy wires from the vehicle to the van so that the fridge can be operated on 12v while driving. At the moment we have to put everything in the waeco while driving and then wait "forever" when we get setup for the van fridge to get cold....far from ideal.

FollowupID: 544628

Reply By: Phillipn - Monday, Jan 07, 2008 at 22:37

Monday, Jan 07, 2008 at 22:37

I attached a 12v fan to the inside of the top vent which pulls the hot air out.

The cupboard top over the 3 way fridge gets pretty warm, but with the fan pulling the hot air out the bench top cool quite quickly and the fridge performs a lot better.

Plus I have a shade set up on the side of the van over the fridge vents to stop the sun from adding to the problem.

Setting the van level is a MUST if you want a three way fridge to perform.

AnswerID: 280388

Follow Up By: Member - Hughesy (NSW) - Tuesday, Jan 08, 2008 at 06:03

Tuesday, Jan 08, 2008 at 06:03

Thanks Phillip. Yeah I was looking at have a shadecloth leantoo made up for the off side of the fan too.

My fridge is a RM2350......I can't find anywhere on how level this model fridge needs to be. Some models are 3deg and others 6deg...not sure about mine.

I've got little spirit levels neear the jockey wheel....but jeeesh 3deg isn't much. I reckon you'd be flat out picking that by eye?????

FollowupID: 544629

Follow Up By: Member - Hughesy (NSW) - Tuesday, Jan 08, 2008 at 06:04

Tuesday, Jan 08, 2008 at 06:04

Yeah I was looking at have a shadecloth leantoo made up for the off side of the VAN too.

Sorry

FollowupID: 544630

Follow Up By: disco1942 - Wednesday, Jan 09, 2008 at 00:20

Wednesday, Jan 09, 2008 at 00:20

Hughesy

All Dometic fridges come with a round spirit level, whether they are passed on to you or not is another thing. You simply place these on the floor or any bench top parallel to the bottom of the fridge. There is a circular green circle in the middle with a raised section around the diameter of the bubble. You simply attempt to get the bubble over this spot. If you can not get this accurately over the raised section, getting the bubble over the wider green sector will get your fridge working at maximum efficiency.

These levels are often seen in accessory shops if you no longer have yours.

PeterD

PeterD
Retired radio and electronics technician

Lifetime Member
My Profile Send Message

FollowupID: 544779

Follow Up By: Member - Hughesy (NSW) - Thursday, Jan 10, 2008 at 15:31

Thursday, Jan 10, 2008 at 15:31

Hi Peter,

Yep I have one sitting in the top draw next to the fridge, but how do you use it when the last thing you do while setting up is lift the roof and turn the fridge on??

Very painful without changing the whole setup of the van to get it operating in its max efficency zone.

I wish they were'nt so finicky, LOL

FollowupID: 545091

Reply By: furph - Tuesday, Jan 08, 2008 at 08:03

Tuesday, Jan 08, 2008 at 08:03

We bought (privately) an off road type of van last year which had been fitted with 2 small computor fans positioned behind the top louvred vent blowing hot air out.
The fans are connected from a thermocouple clamped to the top fins, switching them on when the fin temp. reaches 50deg., and off when drop to 40.deg.
However, the fans run almost continually even on a cool day with the top of the cupboard around the fridge becoming very hot also. The fridge does work well however.
I removed the top (outside) vent for a look see and was most surprised to find a short (about 65mm.) extension on the burner flue and the angled flue pipe (open both ends) was on "back to front" directing all the flue gas back and up into the interior space behind the fridge.
This meant that the 2 fans were not only discharging hot air from the fins, but all the burner gasses too.
I removed the small extension pipe (it looks like a Dometic part) and turned the angled flue pipe round. It aligned perfectly with the hole through the louvred vent, but is now angled up and out, not down and out as previous.
It almost seems that this is how the fridge was installed by the van manufacturer
The result (limited backyard testing at this stage) is that after a full 24hr. period the fans did not switch on until I put 2 x 2l. bottles of water in the fridge when they ran for about 7hrs. then switched off again.
There may (or may not!) be something to look for from my experience with this. On my previous van I placed a single (75mm.) fan horizontally between the fins with baffles a la Collyn Rivers recommendations to very good effect.
furph

AnswerID: 280418

Follow Up By: Member - Hughesy (NSW) - Tuesday, Jan 08, 2008 at 08:40

Tuesday, Jan 08, 2008 at 08:40

Great info thanks Furph.

Yes this is where my curiousness started. I pulled the vents off the side of the van (only had van couple of months) to clean out the dried mud/dust I could see around the bottom. I looked at the litle metal T piece coming off the top of the "furnace" and thought that was pretty bleep weak way of venting the heat as the end of the T was about 3 inches away from the top vent.

However upon cleaning the bottom floor I find this cylinder of aluminium about 4 inches long. Hmmmmmm wonder what this is for.....yes the extension from the top of the T to the side vent. The little tack weld had broken where it holds into the wall vent.

So I fixed this up and thought that would solve the problem of heat on the bench top.....but to my surprise it didn't. Hence now looking at the baffles and computer fan.

FollowupID: 544639

Reply By: furph - Tuesday, Jan 08, 2008 at 12:39

Tuesday, Jan 08, 2008 at 12:39

Hughsey.
Regarding the little "tee" piece, you would see what I meant when I said it was "back to front.
The al. tube is pop rivetted to a plate which is held against the back of the little vent chamber (seperate from the main vent).
This pipe had to point DOWN towards the vent due to the extension on the chimney for the tee piece. Because it is open both ends the heat was all going the wrong way.
When I removed the small extension tube from the burner flue so that the tee piece and al. tube could be turned round, angled up and out, I folded and pop rivetted an end for the low side of the tee piece. This means that no hot gas can escape that way.
There is more than a degree of mystery with these things.
Hope your problem resolves.
cheers furph

AnswerID: 280450

Follow Up By: furph - Tuesday, Jan 08, 2008 at 12:46

Tuesday, Jan 08, 2008 at 12:46

PS
Noticed on your MP you have fitted TurboGlide to your vehicle, as I have recently.
Would like to have a quiet yarn about same,possible?
cheers furph

FollowupID: 544678