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Dometic Fridge Basics
 Some ideas on propane operation

Written by

Curt Long
Maple Valley, WA

I have seen many people, especially new owners, having problems with their Dometic Refrigerators (the ones found in the Vanagon Westfalias up to 1991). There have been many discussions and tips for getting them to work and several I found on Vanagon.com helped me. I have also learned a little more from my personal experiences and from my incessant need to know what makes things "tick". My focus here is tips that will get you going WITHOUT pulling the refrigerator.

Overview

The refrigerator is relatively simple in the way it works. I don't want to get technical here and I am going to describe this in simple terms that I have come to understand. Basically, I picture the heart of the Dometic refrigerator as a chimney with multiple heat sources. Two of the heat sources are enclosed in insulation with the refrigerant tube and located outside the "chimney". These are the heating elements from the 110 Volt and 12 Volt sources. The third source is from the exhaust gases inside the "chimney" from the small propane flame. This flame is not much bigger than a normal pilot light in a gas appliance. The very basic idea is the heat is used to move the refrigerant in the system. That's as far as I want to go into the mechanics of the refrigerant. I only intend to discuss the mechanism that propels the refrigerant; I am assuming that your refrigerant and system of tubes are in working order.

Problems

One of the main problems with the propane portion of this refrigerator is the fact that the exhaust and combustion supply air are at the same level. The propane burner sits at the bottom of this loop between the intake air and the exhaust chimneys. With both intake and exhaust tubes being the same temperature and length, there will be little natural airflow from convection (hot air rising). When the refrigerator is actually in operation, the rising exhaust will pull in fresh air from the air intake, which is under the same cover as the exhaust exit on the outside of your Camper. If you take the cover off, you will see the exhaust in the center and the intake is deeper to one side. The metal disk plate separates them where the exhaust terminates. With the mechanical description out of the way, I can explain the 2 main problems I have learned to deal with:

Problem #1 (gas flow):

Propane is heavier than air and will fill the combustion chamber and both intake and exhaust tubes if you fail to light the gas quickly enough while there is still oxygen in the lower chamber. With out any air movement, this propane will remain in the bottom of this loop for many minutes (maybe even indefinitely until something displaces it). The air pump on your ignition plunger is designed to help displace the propane and supply oxygen to the burner. However, this air pump often has problems and many do not work well, if at all. (The Bentley manual describes a method for modifying this pump to improve the airflow). I have learned how to get around this little pump.

Solution #1A (forced air):

If you think the combustion chamber is flooded with propane and your air pump is weak, go outside and find the exhaust tube just under the final shield of your exhaust cap. You can blow hard across the exhaust tube opening (and just under the final cap) at close to a 90-degree angle and form a slight vacuum that will pull air and propane out of the exhaust tube (due to the venturi effect). This will also pull fresh air down into the combustion chamber. If it is working, you will smell and maybe even see the propane as it comes out in a cloud. If you have another air source handy for blowing across this plate then use it. But I have found about 4 full breaths blown hard and at the right angle will clear the flooded condition. I rarely have to do this twice. Now, go back and hold the gas button in and immediately and REPEATEDLY push the sparking plunger till it lights. If after 20 seconds, you don't have it lit, it may be flooded again. And after trying this 3 or 4 times with no results, try solution #1B or go to problem #2

Solution #1B (preheating):

If you have the time or maybe you're not interested in doing the blowing trick (or have not gotten the hang of how to blow across this plate), plug your refrigerator into 110 AC Power and turn it on. Or, switch to 12 Volt with the engine on or while driving (the 12 Volt power is designed to cut off with the engine off to preserve the battery in most Westies) After about one hour, the 12v heating element should have heated the chimney as well as the refrigerant so that there is now an air flow loop happening in the intake and exhaust tubes. The propane should be clear and you will have much better luck lighting the propane. Also, the heated chimney will help keep the air flowing into the combustion chamber while you are lighting the propane and will minimize any chance of propane flooding.

Problem #2 (mechanical obstruction):

The exhaust chimney is not rust proof. Over time, the condensation from the propane flame and even outside water sources will rust this pipe. The rust scale and flakes will fall back into the combustion chamber and short out the spark igniter or divert and even clog the gas orifice. Many times, this rust scale is loose and dry and can move around freely. However, at the bottom of the combustion chamber, there is nothing to move it around. It doesn't take a very large flake of rust scale to bridge the spark gap on the igniter. And a small flake of rust can deflect the propane away from the spark so that the chamber floods before the propane is ignited.

Solution #2A (vacuum trick):

Remove the protective exhaust cap from the outside of the camper. Should be 3 small stainless screws. Remove the metal disk from the end of the exhaust tube so that a vacuum cleaner hose can fit over it. I place a loose weave cloth like cheesecloth over the vacuum hose to trap any debris. This allows me to confirm the presence of rust and tell when I have all that will come out. The strong airflow should move the rust flakes and most if not all should be pulled out. You may also want to try compressed air down into the exhaust tube, but I prefer to use the vacuum, as it is less likely to cause damage and will insure that any new flakes ready to drop will be extracted and not first pushed down into the combustion chamber. Now, go back to the lighting procedures including solutions #1A and #1B if needed.

Solution #2B (pull the fridge):

Remove the refrigerator and open the combustion chamber. Clean out any rust and look to see that the spark gap is clear and working. One time I had something that formed a bridge across the spark gap that was not simple rust. Never did find out what caused it, but it was a simple fix with the combustion chamber open. You might also clean or replace the metered gas orifice at this time if you have the part. DO NOT insert anything into the orifice - it should only be cleaned by soaking in alcohol and then blown out with compressed air)

Instructions for removing the refrigerator are available in the Bentley, and in the archives. Whatever you do, take care to reconnect the propane line carefully and check for leaks as described in the Vanagon.com article for removing your Dometic refrigerator. And DO NOT under any circumstances, ignore the smell of propane if you have tampered with the propane connection... Close the main valve at the tank until you have eliminated any leak cause by removing the refrigerator.

Solution #3B (the easy way out):

Take your refrigerator (or drive your Westy with Refrigerator installed) to a repair shop that works on Dometics... there have been some good shops suggested by many on the lists. P.S. It's NOT Rocket Science! :-)

Curt Long,
Maple Valley, WA
'87 GL Syncro Westy
'71 Riviera Camper