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Correct Gas/Electric Fridge Venting

Article by Val Rigoli ©, free advice freely given, my personal thoughts and advice gathered from in-excess of 45 years of practical hands-on experience, learned skills, and industry knowledge.
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DOMETIC RGE400 Gas/Electric FridgeDOMETIC Vent DOMETIC RM2350 Gas/Electric Fridge
The Venting on a Gas/Electric Fridge is so very important for correct fridge cooling operation.
Sadly far far too many people have had very bad experiences with their fridges not cooling well enough,
or not staying cool enough in warm weather.
 Most of the time this is caused by poor or wrong venting.

Venting of a 
Gas/Electric Fridge is NOT about how much venting the fridge has,
but it IS all about how much correct venting the fridge has.

The information below will help you understand how the vents are designed to work,
and how they must work if the fridge is to perform well in warm weather.

FRIDGE & SOLAR would like to thank RV Mobile Inc. 11715 HWY 99, Everett, WA 98204  for the use of the information below over the past 17 years.

The venting of an RV gas/electric refrigerator should be designed to not only provide a place for the warm air from the cooling unit to escape, but designed to actually create a draft that will remove expelled heat as efficiently as possible. Poor venting can cause the cooling unit to overheat and damage the cooling unit.

When the cooling unit gives off heat, it causes air around it to warm. Warm air rises causing cooler air from the lower vent to enter the area and to extract more heat from the cooling unit and also rise. The greater the difference in temperature between the warmer air and the cooler air, the faster the air will rise. Narrowing the path of the air flow forces the cooler air through the cooling unit coils as it rises.

When installing a refrigerator, it's also a good idea to isolate the sides and the top of the refrigerator from the rear, preventing heat from accumulating around the box and hampering the effect of the refrigerator wall insulation.

Val's note!! please read the above 3 paragraphs again, it is most important to truly understand this drafting effect and convection!

The roof vent, which caps off the venting, keeps the rain out but allows for good air flow. The roof vent is centred over the cooling unit and is as at least as long as the cooling unit is wide.

In the venting side views below, the roof vent appears to be fairly small. But, in the front view above, you can see that it covers the entire width of the cooling unit.

Fans. Theoretically, perfect venting will create a draft that will remove heat from the cooling unit in even the warmest conditions. However, perfect venting isn't always that easy to achieve. The purchase of an add-on fan can solve a lot of problems in border line venting, but is not a cure all for terrible venting. The important thing to remember is that the fan should be installed above the cooling unit, preferably right at the roof vent. The purpose of the fan is to improve the draft, not to blow air onto the cooling unit.

Below are three examples of good venting under different situations.

Gvent1.gif (3291 bytes)          

Bad Venting: The picture below demonstrates two venting problems. The distance between the cooling unit and the outer wall is greater than 1" allowing air to by-pass the cooling unit. Besides not extracting heat from the coils, cooler air by-passing the cooling unit tends to cool the warmer air at the upper levels and weaken the draft. Also, there is a dead air space above the refrigerator. A dead air space or cavity at the top of the refrigerator causes warm air to accumulate, drastically reducing air flow.

It's best if the upper roof vent is top mounted. Sometimes circumstances prevent the use of a top mounted vent, and an upper side vent is the only solution. An upper side vent will work if done properly and only with the smaller refrigerators (5 cubic feet or less). Below are the right way and the wrong way to do this.

Gvent4.gif (3577 bytes)            Badvent2.gif (2942 bytes)

Val's note!! the upper vent must be placed above the fridge, and it is very important to use the DOMETIC branded vents, these offer far superior venting, much more than any of the aluminium or plastic fluted vents, also it helps even further if you can fill in between the baffles with styrene foam or anything else you can think of, but cover it with aluminium foil to make it somewhat fire proof.

The 12V side of these Gas-Electric fridges often has issues.
It can be a huge problem with these fridges when folks run them on 12V.
(The fridge is NOT at fault, it is a common fitting fault!)

First up, just in case you were not aware, gas/elect fridges are only ever meant to be run on the 12v circuit when you are driving,
otherwise they are built and designed to run on gas, or 240v most of the time.

These fridges by design use heating elements to make them work on both 12v and 240v,
and there is no thermostat (to turn them on and off) built into the 12v circuit on many of these fridges,
the newer AES (Automatic Energy Selection) models being the exception.

This means that when running on 12v the fridge runs constantly and draws at least 10.5 amps (smaller fridge) per hour,
this would mean that over a 24 hour day it would consume at least 250 Ah and much more for larger fridges (think double that)!!

Of course there is no way you're going to keep up with that sort of power draw or would want to even try,
so it's best to run on 240v when mains power is available, and on gas when you're parked up away from mains power,
and only use 12v when you're driving.

This leads us to the next biggest common problem.

I don't know how many times I've heard the claim that these fridges don't work on 12V, or at least not very well.

If the fridge is not working well on 12V, but works ok on gas or 240V, then this is always a wiring problem, every time,
The wiring is either not heavy enough, or there is a loose connection, or both,
no ifs and no buts!!

Upgrading the 12V wiring will not cost a lot and is always well worth it, I always suggest for the fridge cable size
8 B&S (it's around 8mm²),
and please do both positive and negative wired direct to/from the battery.
I suggest that folks use this size cable on all fridges, it is a one off expense that is very well spent.

The problem in many cases is not only the wrong wiring size,
but also the wire/cable run distance between the batteries and the fridge (both really do go hand in hand).

Often there are wild amounts of wiring running halfway around the motorhome or caravan to a control panel,
then feed through a couple of switches, and some fuses, then toss in a dozen connectors,
and then meander some wires to eventually terminate over at the fridge.

Is it any wonder that the fridges poor little 12V heating element that really needs all the current it's designed for,
and at it's designed voltage (12V+), has so very little chance of performing well.
Most of the time a lot of the energy it needs to make heat,
is lost in making heat along grossly inadequate wiring along poorly thought out wiring routing.

Sadly this is not the exception, it's almost the rule.

So regardless of if you do or do not have problems right now,
it would be well worth a serious re-think about the size of the cable running to the fridge,
and where the cable is routed (for the shortest possible run),
and if found inadequate, replacement/upgrading this cable,
will most certainly vastly improve the performance of the fridge on 12V.

For other RV related articles you may find interesting please check my Tech page

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