Home | Member Access
Roadtrek International Chapter, FMCA

the great Refrigerator Fan Experiment

Harvey Tetmeyer K5LJM - Silent Key 5 Feb 2005 

In our trip to the mountains, the refrigerator did not perform on propane as it should... even in cooler weather. When we returned home, I blew the debris out of the burner assembly with compressed air, turned the refrigerator to propane and monitored the temperature. As expected, the unit worked much better on AC than propane.

Further checks revealed that the propane regulator pressure was running 8 to 9 1/2 inches of water rather than the desired 11. Since the little refrigerators are very finely tuned to perform to the minimum gas industry specifications of cooling to 42 degrees F in a 95 degree F environment, this would make a difference... a big difference!

I took the van to the shop for the annual maintenance, as required by the Dometic extended warranty, and asked them to replace the regulator. This was the second regulator to go bad. The first one was replaced under warranty at about six months, which was within the regulator's one year warranty. This replacement was on my nickel. The tech said there was also some rust in the flue that could further degrade performance.

The following measurements were made when the van was returned from the shop.

As indicated, this particular refrigerator cools better on AC than propane. Cooling on AC is quite dependent on line voltage and our service runs on the high side here at this time.

It came as no surprise that an external fan makes a big difference in the refrigerator internal temperature in hot weather. One of fans pictured below was replaced with a higher output, but quite noisy, fan of the same physical size. This allowed testing at approximately 25, 100 and 125 cfm. The smaller fan is adequate in most situations but the larger fan does a little more cooling.

A small blue battery operated fan was placed in the bottom of the refrigerator.

The refrigerator was not opened during the test. In use, the temperatures would be higher due to hot air being exchanged for cold air when the door is opened and from warm items being placed in the refrigerator.

The refrigerator was empty during the test. In previous test, five quarts of 45 degree F water were placed in the unit. As expected, the temperature swing was much less due to the "thermal mass" of the water.

Testing will be done to evaluate 12 VDC operation when time, appropriate weather and test equipment are available. Preliminary tests indicate that even though there is not that much difference in heat applied with the 117 VAC and 12 VDC heaters, cooling is much different. This goes back to the fine tuning of the cooling units. Not enough heat will reduce cooling. Too much heat will cremate the cooling unit.

From what I have seen, I plan to run the 25 cfm fan, which draws very little current and is not noisy enough to bother us when we are out camping in the woods.

Update 9-3-03

The mice got in the outside of the frig and chewed the igniter wire so I had to make some modifications... but it was about time anyway. I removed the two little fans and put in some hardware cloth, where the fans had been located, to keep out the little pests.

But it was still hot in Arizona... 100 -110F...

In looking through the junk boxes, I found two each four inch 1/4 amp 12 volt DC muffin fans that looked like they would work. Since I could not reach up in between the refrigerator cooling coils and the vent grill, I decided to try fastening them on the outside. I grabbed a fist full of black tie wraps and finally fished four of them through the top vent grill to attach the fans. I stuck the fan up using four more tie wraps. The fans are spaced about 1/8 inch away from the grill and should not scratch the grill... in case I want to remove them later. --- I'd paint the blue labels black but the fans get more attention this way.

So how do they work... you ask? G-R-E-A-T !
(What else would you expect me to say?)

We just returned from the Sierra Rolling Rally... which was great too...and points West. The trip included several hundred miles of driving and several days sitting still in the low desert, high desert and mountains... with temperatures ranging well up in the triple digits several days... mainly going to the rally and coming back home. The refrigerator was much cooler and performed very well the whole trip... even on DC!

While I do not have any quantative data at this time, it looks like the fans will help make up for the refrigerator installation's limited venting system. The cost is the price of the two fans and the additional half amp 12 volt load. The fans have about the same load as the safety sensors, so I do not consider it a problem. Either one, or both, will run your battery or batteries down in a few days if the 12 volt switch is left on and the van is not plugged to the AC.

In the next few days/weeks, I hope to make temperature measurements with and without the fans. I would also like to know if one fan would move enough air to keep the frig working efficiently.

End of up date... but probably not the end of refrigerator issues ----

I was interested in experimenting with increasing the air flow over the "hot coils" in the back of the RV refrigerator to see if I could improve cooling. The top vent on the Roadtrek is rather difficult to remove so I installed two small high output (12 volts @ 0.21 amps each) muffin fans on the lower grill.

The test configuration is shown in the picture on the right. Two fans, approximately 3 3/8 inch square by 5/8 inch thick were fastened using common plastic tie wraps.

The location for the fans was selected to miss the plastic ribs sticking out from the top of the vent frame attached to the van.

 

The plastic fins near the centers of the fans were trimmed slightly to clear the fan blades.

A miniature switch was installed through a hole drilled in the vent assembly. This allows manual operation of the fans from the outside of the van.

If the tests yield promising results, I will probably put a switch on the inside of the van.

 

First the disclaimer... This setup is just for testing, right now. It is not intended as a permanent installation, unless it works and endures the RV environment. The fans are not rated for outdoor use. The tie wraps will give out sometime in the desert climate. All the parts were from surplus equipment, bought for pennies on the dollar at Amateur Radio hamfests.

The results so far are... as reported on the CyberRally

"I turned the refrigerator on in 100 degree weather with the sun shinning on the
refrigerator side of the van. Internal refrigerator temperature was 99 degrees. Internal temperature was measured with a remote readout RV refrigerator thermometer. Cool-down was about 10 degrees per hour. This morning, the outside and van inside temperatures were 86 degrees. The refrigerator temperature was 26 degrees."

I plan to run more qualitative tests in the next few weeks with the fans turned on... then turned off... a real comparison.

Results will be posted here when the data is analyzed and sufficiently pencil whipped... i.e., presentable for tacking on the net.

On to practical installations for RVs... A number of different kinds of external fans are available from most RV retail stores. They usually consist of kits including a fan, a switch... sometimes a thermal switch and/or a solar panel to power the fan. They are normally mounted above the refrigerator in the upper part of the vent. To install this type of fan on a Roadtrek, I think the outside vent would need to be removed or the refrigerator pulled out to give access to the area where the fan goes. Shop