Thread: Fridge Advice

Originally Posted by Blknight.aus

they usually run a constant flame and it gets as cold as it can, the operating principle is not like a hot water system.

We have had 3 Electrolux / Dometic units over the years (still have one). All 3 used a pilot and a thermostat. The (relatively) new unit in mum's van uses thermostat and electric start rather than a pilot.

Originally Posted by BradC

We have had 3 Electrolux / Dometic units over the years (still have one). All 3 used a pilot and a thermostat. The (relatively) new unit in mum's van uses thermostat and electric start rather than a pilot.

closest Ive ever seen (and I generally avoid absorbsion refrigeration like a vegan does a steakhouse) was one that had dousers on a bi metal strip setup with a kero wick, (yes I'm old) and the small camping 3 ways that just run a constant small flame. Im also usually pulling them out to put in compressor fridges with a battery upgrade. Even thats not a super regular exposure for me... wonder how they do the regulation if its running gas only?

Originally Posted by Blknight.aus

wonder how they do the regulation if its running gas only?

The unit I have in the van parked out the front is bang-bang control. One jet, two flame sizes and adjustable thermostat that switches the gas flow up and down. The one we had on the boat (before ripping it out and replacing it with a compressor fridge) did the same thing.

Reading the Dometic service manual I have here they use the term "low flame" rather than pilot, but when you look at the gas thermostatic valve schematic it's pretty clear. Small "bypass" channel for the "low flame" and switched "main" channel for the "want more cooling" flame. The fridge in the van uses a prismatic reflector and you can clearly see the flame size change as you play with the thermostat.

Edit : Managed to OCR this from the service manual glossary.

Code:

GAS/ELECTRIC THERMOSTAT :current Dometic manual refrigerators, this device is held in place with "0"" ring seals in the gas line and replaces
separate electric and LP gas thermostat controls. On the LP gas mode, full line pressure is
directed through the thermostat to the burner until the thermostat senses that the
refrigerator cabinet has reached proper cooling temperature. At that rime an internal valve
closes and redirects the gas flow through the by-pass screw. This reduces the amount of LP
gas going to the burner assembly. The gas flow remains in this “by-pass” mode until the
thermostat senses that the refrigerator cabinet needs more cooling. Again, the thermostat
directs the LP gas flow through the thermostat at full line pressure until the cabinet
temperature is sufficient.

Originally Posted by RANDLOVER

To pull all of this thread together, I agree with Black Knight, your principle is sound, and with Brad that you have to improve heat rejection, which your compressor and evaporation plate will do, not sure if over cooling would trip out the gas, or if it would just go down to pilot flame setting. Surely it cycles off on the thermostat in normal operation and doesn't have to be re-lit?

My fridge has auto light on the gas. I am not sure whether it shuts down or heavily reduces gas flame.

My concern with what I want to do is this. In the instruction manual it states that if the fridge is used in a very cold environment,
that due to the thermostat being in the fridge, the freezer won't work.

By putting the extra cooling in the fridge, the thermostat thinking that the fridge is cold enough, will shut down and the freezer will then suffer.

As I said earlier, I could probably get around this, if it happened, by putting some insulation around the thermostat sensing bulb.

I would hate to spend the money to get a really good fridge only to lose the freezer.

Below is a copy and paste from the instruction book.

When ambient temperatures are lower than
+10°C and the refrigerator is exposed to
these temperatures for extended periods of
time, an even regulation of freezer tempe-
rature cannot be guaranteed for system-
related reasons. This can cause the tempe-
rature in the freezer to rise and the stored
goods to melt.

Yep, that will happen if it cycles on thermostat. You won't mitigate that by insulating the thermostat. It'll still cool to fridge ambient, just a little bit slower.

What you *could* do however is set the thermostat on the isotherm a degree or two warmer than the thermostat in the fridge. So in cool ambient with the thermostat wound all the way down, see how cold you can get the fridge and set the thermostat on the isotherm a degree or two above that. In theory in hot weather the fridge will never get down to cold enough to shut off the absorption cycle, and in cold weather the isotherm shouldn't kick in and you're where you are now.

For something different, a really revolting work-around is you insulate the fridge thermostat with a small power resistor up against it in the insulation and apply power to that when the isotherm is running. So when the isotherm is actually working you are heating the thermostat bulb in the fridge forcing the absorption to run flat out.

Thanks Brad. If I go down this path I would only run the Isotherm when the ambient hits say 28 degrees.

I would put in an isolation switch and turn it off. It would only be used as a booster in hot weather.

I love your idea of using a resister to warm the thermostat.

Could you put the the evaporator plate from the Isotherm in the freezer compartment.

Then set the gas to full cold, and the Isotherm thermostat at a temp to give acceptable fridge temp.

Does the Isotherm have a separate thermostat, or is it built into the evaporator plate?

We're is the fridge thermostat? In the fridge or the freezer?

It seems like a lot of money given what a Dune/Kings/Brass Monkey fridge costs.

I have an old Engel here that is either low on gas or the insulation has broken down, it was running, but using a lot of power last time I used it.
Your welcome to it if you want to try and gut it for the refrigeration side.

Tony

Originally Posted by TonyC

...................
I have an old Engel here that is either low on gas or the insulation has broken down, it was running, but using a lot of power last time I used it.
Your welcome to it if you want to try and gut it for the refrigeration side.

Tony

Consider this issue before you write it off...............

'Bit of grave dig, but I'm interested if other brands have this 'issue'.

I haven't used the 40l Primus for quite a few years, no need really.

The last time I used it there seemed to be a problem............. fan was screaming and it wouldn't come down all the way to set temp.

Was out of warranty, had bit of a look at the time at the internals, thinking it's maybe munted, aka Ron B's luckless purchases.

Anyway recently I had to move it from one property to another and I had bit of time to take it out of the cover and have a closer look.

The problem was somewhat obvious, dunno why I didn't see it before. Condenser has a screen attached to the front of it like metal flywire and it was covered with a film of fibrous dust (a bit like what you'd expect from carpet from a 1974 RRC cargo area ). It wasn't plastered in it but it was there.

I pinched the slots in the stainless casing a bit wider with pliers so I could get a fine brush in there and vacuum it out (rather than blasting it all through the casing with an air gun).

Plugged it in to 240, set it to -!0c and away it went, like new. Left it running for a month and it's faultless, even the remote wireless in cab temp and voltage thing works perfectly.'

And it was faultless on an extended bush trip last year, set to 1 degree C and used hardly any power.

DL