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Oil Contamination in LP Gas Systems

Liquid propane gas (LP) packs a large amount of energy into a small package. As a result, it’s an economical choice for RVers, and it is used for heating, cooking and to power the RV refrigerator when AC power isn’t available. My wife, Mao, and I run our business for six months of the year from our RV, never using shore power!

The story begins when we were camped at Boomerville, in Quartzsite, Arizona, for the annual January get-together. Mao and I were performing installations of our product, Fridge Defend®. A group of folks was gathered around having a good time, seeking knowledge and sharing stories while I worked. This is simply the way we Escapees operate, and we love helping other RVers in need. That is what we are about! A gentleman came over and asked me if I was an RV tech. I said, “No, but I can help you with your refrigerator if you have an issue.” I finished my work and went over to investigate his problem.

I learned that he began having problems with his propane system after he filled his LP tank. He had replaced his LP regulator but did not know why it had failed. His main issue was his refrigerator. When he found that it was not cooling on LP, he was wise enough to discontinue its use. I say wise because he could have created a dangerous situation by continued use. I’ll cover this issue more later. Being Boomerville, we were all boondocking. He was able to power the refrigerator with his generator, but no one wants to run a generator all day and night as it’s too much exhaust and noise nuisance for happy neighbors! 

Visual Inspection

One Must Be Qualified To Perform a Pressure Test

Because the refrigerator worked on AC power but not LP, the first thing we did was open the burner housing to perform a visual inspection. We found there was brown oily residue below the burner. This was the proverbial smoking gun! We immediately understood why his LP regulator failed and why his refrigerator was not working on LP. When his tank was filled, he got a batch of oil in the LP. It’s rare, but it happens. The oil can get into the system and destroy the LP regulator, plug burners and filters.

This was the first time we have witnessed such an extreme case where oil actually came out of the refrigerator gas jet and collected on the bottom of the burner housing. The refrigerator was at least 18 feet from the tanks, and it takes a lot of oil to flow this far.

Ordinarily, oil contamination in the LP system is checked for in one of two ways: The first and most scientific method is to do a pressure test somewhere in the LP lines to make sure that the pressure regulator is supplying 11 inches of water column (11″ WC) gas pressure. The LP bottle and regulator are to the left. A drawing of a manometer attached to the LP regulator test port shows the principles behind the pressure test; the purple represents the water in the manometer. One must be qualified to perform this pressure test, so we will not go into manometer details here. What is to be understood from this drawing is that, if the pressure is 11″ WC at the regulator, and then the manometer is moved to the fridge solenoid-operated valve (SOV) ‘gas jet pressure test port’, and say 8″ WC is measured, then lower pressure is measured. The probable cause is a plugged SOV gas filter.

Cleaning the Filter

This brings us to the second method. After reading the above, one can understand what can go wrong, and then go directly to the suspected problem. This is exactly what we did. We were not carrying a manometer with us; we knew that there was an oil contamination issue by the evidence in the burner of the fridge, so we proceeded to go directly to the LP filter within the SOV valve.

We disconnected the LP supply line from the SOV valve after turning off the LP gas at the tank and bleeding off the residual pressure by lighting a burner on the stove. Once the inlet line is removed from the SOV valve, the Norcold refrigerator SOV has a foam filter that can be removed with a toothpick. (For most Dometic refrigerator SOVs, the filter is ceramic and has to be cleaned in place by flushing with 91 percent isopropyl alcohol.) The Norcold filter was placed into a glass jar with 91 percent isopropyl alcohol.

Finally, because of all the oil in the burner housing, we knew that the LP jet was contaminated. This was quite evident when, after removing the line from the SOV to the gas jet, oil began running out of the line. Once the jet was removed, we could look through it into the sunlight to see how restricted it was. We put it into a glass jar with the 91 percent isopropyl alcohol to soak. Naturally, we flushed out the line from the SOV to the jet, but it was getting dark and we had to finish our job before we lost light.

To finish the job, we installed the Fridge Defend®. Why? As mentioned above, when the fridge is not cooling, it is because the boiler on the refrigerator is overheating. The only way to tell that the boiler is overheating is to install the Fridge Defend®. Thus, as stated above, the owner of this fridge was wise, because he could have overheated his boiler to the point that it ruptured. This is how refrigerator fires occur.

How Fridge Defend® Helped

You may ask, with the propane supply partially blocked by oil, how can the fridge overheat? If the blockage was complete, and there was no flame at all, it wouldn’t harm the fridge. However, because of the design of the boiler, too little heat is almost worse that too much! If the flame is too low, the reduced heat at the boiler will still boil off the ammonia without causing the necessary pumping action, leaving the cooling system stalled. No circulation in the cooling system will allow the boiler to run dry and overheat.

We buttoned up the job during a beautiful Quartzsite sunset, started the fridge on LP and checked for normal boiler temperatures on the Fridge Defend® display. Satisfied, we headed into the desert to enjoy the evening.

The next morning, we called to see how the evening went with the repaired refrigerator. Well, we had an unhappy customer because the Fridge Defend® turned the fridge off during the night. We explained that the jet and/or the filter was probably plugged with oil again, resulting in overheating of the fridge boiler. Hearing our explanation, the customer was pleased to find that the Fridge Defend® had done its job by protecting him and his RV.

We went out to the RV again and did our best to flush as much oil out of the lines as possible and suggested that the owner have the system flushed again if the problem continued.

Conclusion

Oil contamination can be a problem in LP gas systems. It is introduced during a fill of the LP bottle, and the oil can plug jets and filters in the LP system. Oil in the LP system is particularly dangerous for Dometic or Norcold refrigerators because they have a filter in the SOV valve, and the gas jet is very small. Oil accumulation in the LP jet or filter can result in the fridge cooling unit boiler overheating, and only the Fridge Defend® by ARP can protect the fridge if this happens. The oil contamination can be cleaned out of the system by disassembly and flushing with 91 percent isopropyl alcohol. Acetone can also be used to clean the pipes, but you must not let it touch any rubber or plastic parts. Be sure to leave the LP system open long enough for the solvent to evaporate. If you know that you have oil contamination in an LP bottle, when the bottle is empty the valve can be removed, and the tank can be turned over to flush and drain the oil. 

Author

Paul & Mao Unmack

PAUL AND MAO UNMACK are mechanical engineers. Paul ran an automotive repair business in Red Lodge, Montana, for 20 years before receiving his engineering degree. He has practiced nuclear, fire suppression and industrial process control systems design. Mao designed pressure vessels for ammonia plants, in China, for 12 years, then came to the U.S. to get a master’s of welding engineering. She designed biodiesel plants and worked for a government- funded research and development organization. Paul and Mao run the entire ARP control business while taking on engineering consulting gigs. 

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