Another Reefer Question July 19, 2010, 01:33:04 pm Yahoo Message Number: 114609Copied below is the message I sent Dometic. I received what I'd describe as a non-answer from them. Anyone have an idea? Reefer is brand new, under warranty. I had a Dometic RM2620 installed in our motor home on 4/23/2010. It cools fine on either AC or gas when it is stationery. But when we are driving down the road, whether on AC or gas, the temp rises, and rises rather quickly. Here's a test I ran today. Outside temps were in the mid 80's. Thermostat set at 3. Had been cooling on gas since Tuesday PM [test was run Saturday AM]. Depart 1045 AM, Freezer temp 2.7 F, Reefer temp 41.5 F, power source AC Generator. Arrive 1110AM, Freezer temp 5.0 F, Reefer temp 43.5 F, distance driven - 19 miles. At 1115 AM generator turned off so automatically switched power source to gas. Depart 1215 PM, Freezer temp 9.1 F, Reefer temp 50.2 F, power source gas. Arrive 1245 PM, Freezer temp 14.9 F, Reefer temp 55.4 F, distance driven – 19 miles.LP on inside gauge and tank gauge shows between ¼ and ½ full.This is a brand new unit professionally installed.John & Cheryl 1994 22' TK Chug
Re: Another Reefer Question Reply #1 – July 19, 2010, 02:14:18 pm Yahoo Message Number: 114611QuoteCopied below is the message I sent Dometic. I received what I'd describe as a non-answer from them. Anyone have an idea? Reefer is brand new, under warranty. But when we are driving down the road, whether on AC or gas, the temp rises, and rises rather quickly. John & Cheryl, It is just a hunch and maybe not valid but I suspect those symptoms would be caused by the airflow over the roof causing a downdraft in your refrigerator vent chamber when you are moving. If the roof cap is designed and installed properly it should cause a slight vacuum in that chamber to pull the hot air up and out. If it actually causes pressure to rise in the chamber the only place for the hot air to go is horizontally and there are too many things in the way for that to function very well. I have always had higher refrigerator temperatures on our mid bath when traveling and recently replaced the cover on our vent to test my theory but it may be a couple of months before I know if it really has any effect. The temperature rise in our unit is not nearly as fast as yours but after a day of travel the refrigerator is frequently over 50 degrees even on moderate days.MontiMonument, CO
Re: Another Reefer Question Reply #2 – July 19, 2010, 02:20:28 pm Yahoo Message Number: 114612"John" wrote: Copied below is the message I sent Dometic. I received what I'd describe as a non-answer from them. Anyone have an idea? Reefer is brand new, under warranty. --- In my experience, expecting a useful answer from Dometic is akin to waiting for manna to fall from the sky; neither is likely. I'd call the place where you had the refrigerator "professionally installed" and also check this website for troubleshooting help:http://rvmobile.com/Joan
" Reefer"!!!! Question Reply #3 – July 19, 2010, 03:36:26 pm Yahoo Message Number: 114615Ok have to say when I see "reefer" question my first thought is ---pot...I don't smoke it but I did grow up in the 70's and that was a common term....LOL.Funny how times have changed...now it means a refrigerator!! DAlaDar Beagles www.aladarbeagles.com
Re: Another Reefer Question Reply #4 – July 19, 2010, 03:45:41 pm Yahoo Message Number: 114616"It is just a hunch and maybe not valid but I suspect those symptoms would be caused by the airflow over the roof causing a downdraft in your refrigerator vent chamber when you are moving."John & CherylThere is a good chance Monti has found the problem. We get a slight rise in temperature while driving but that would be over many hours, not minutes. Since your refrigerator has been replaced, going over how the cap and vent are installed would be the first place I would look. Who knows what was done to get the new unit to fit into the space the original refrigerator was located. You should have received the installation manual along with the owner's manual. It will have the specifications for fitting the vent and cover. The installation manual is probably available online.Larry
Re: " Reefer"!!!! Question Reply #5 – July 19, 2010, 03:55:50 pm Yahoo Message Number: 114618And those who are sufficiently aggravated by their refrigerators' whimsies will succumb to Reefer Madness! ;-)J.
Re: Another Reefer Question Reply #6 – July 19, 2010, 03:56:59 pm Yahoo Message Number: 114619During your first drive, the temperature rose 2.3 degrees freezer/2 degrees fridge
Re: " Reefer"!!!! Question Reply #7 – July 19, 2010, 04:51:29 pm Yahoo Message Number: 114620"Ok have to say when I see "reefer" question my first thought is ---pot...I don't smoke it but I did grow up in the 70's and that was a common term....LOL."Ruth You are showing your age . That is the term I heard my dad use when I was a kid. As a grade school student, I was lucky enough to see the Reefer Madness comedy movie before it was finally pulled from usage. I wonder how many people it lead to marijuana use? Reefer is a term used to describe refrigerated rail cars for over a hundred years. Somewhere, it was also applied to refrigerators. http://en.wikipedia.org/wiki/Refrigerator_car>Larry Listening to a discussion on NPR about the marijuana legalization proposition on California's Novembers ballot.
Re: Another Reefer Question Reply #8 – July 19, 2010, 04:55:53 pm Yahoo Message Number: 114621John,Read my response to a similar question in the post #109176: http://autos.groups.yahoo.com/group/lifewithalazydazerv/message/109176The problem is an "air dam" at the roof vent and the answer is a fan at the top of the fridge chimney just under vent cover. And, as far as Joanne's comment about the temperature drop while the rid was stopped goes, did you stop for lunch and open the fridge? Alex Rutchka, SE #4 '05 MB
Re: Another Reefer Question Reply #9 – July 19, 2010, 04:59:46 pm Yahoo Message Number: 114623As Joanne pointed out there may be other variables. I know that with our rig the refrigerator is sensitive to whether the sun is on the refrigerator side. Where the sun was during your trip may confound your numbers.Safe travels,Dave N 2000RB Albuquerque
Re: Another Reefer Question Reply #10 – July 20, 2010, 08:24:49 pm Yahoo Message Number: 114648And, as far as Joanne's comment about the temperature drop while the rid was stopped goes, did you stop for lunch and open the fridge? No. The point about the temp rising as it sat for an hour is well taken. What I should have said is it cools down and stays cool just fine before leaving on a trip or at the campsite. It's the in-transit time that's the issue. I did talk to a local tech and he confirms many of the ideas here. Somehow air is not passing over the cooling coil. Whether downdraft, stagnant, no idea. Will test some more this weekend and see what happens and let you know what I find out, if anything.Thanks all for the ideas.John & Cheryl Chug
Re: Another Reefer Question Reply #11 – July 20, 2010, 09:11:18 pm Yahoo Message Number: 114649How about an air scoop on the exterior fridge access door? Your local speed shop could probably outfit you with something, or maybe one of these would work:http://tinyurl.com/25kgx25>I think this one looks especially snazzy ;-)http://tinyurl.com/2asxcvv>Andy Baird http://www.andybaird.com/travels/
Re: Another Reefer Question Reply #12 – July 20, 2010, 09:33:13 pm Yahoo Message Number: 114651Alex; 109176. Any chance you could take a picture of how it is installed?John & Cheryl Chug
Re: Another Reefer Question Reply #13 – July 20, 2010, 09:37:19 pm Yahoo Message Number: 114652Andy;Doesn't Radio Shack have something that would work?John 1994 TK Chug PS-I think there's something to this air flow idea. Big Red, our 1989 RL, had the reefer where LD puts the wardrobe now, about 5' further back in the rig. The newer TK's swap the wardrobe and reefer, putting the reefer closer to the front. Our old reefer in the TK had the same temp problem and since it was the original reefer I figured it was on it's last legs. Now the new one shows similar tendencies. Hmmmmm.
Re: Another Reefer Question Reply #14 – July 20, 2010, 09:57:20 pm Yahoo Message Number: 114653OK, John. I'll try to do it in the morning before the heat of the day arrives. The vent cover needs to come off to expose the fan which as I recall is suspended across the chimney with plastic zip ties. The key thing about the PC cooling fan selection was that it be efficient and have a ball bearing motor for long life. Or, at least that's what the fridge tech said.Alex Rutchka, SE #4 '05 MB
Re: Another Reefer Question Reply #15 – July 21, 2010, 10:05:57 am Yahoo Message Number: 114654"Doesn't Radio Shack have something that would work?" Radio Shack doesn't sell scoops, if that's what you mean, but my suggestion was tongue-in-cheek anyway. Truth is, I think a small scoop would probably do a good gob of ensuring airflow over the refrigerator coils while driving (if it didn't blow out the gas flame, that is), but it would have to be removed when parked. More trouble than it's worth. With regard to mounting a fan at the top of the fridge's cooling stack, it can't do any harm, and it may help when parked (thought I have yet to see proof of this)... but I have my doubts about how much good it will do when driving. When you think about it, a small 12V fan doesn't stand much chance against a 60 mph air stream. A better solution would be a redesigned fridge vent cover, shaped to create negative pressure and thus extract air from the space below it. Maybe one of our members with aerodynamic expertise could come up with something... :-)Andy Baird http://www.andybaird.com/travels/
Re: Another Reefer Question Reply #16 – July 21, 2010, 10:34:44 am Yahoo Message Number: 114655John, Pictures of the fridge vent fan, thermostat, and switch have been posted in the Photos area here: photos/album/986711196/pic/list12 volt power is picked up in back of the fridge at the connection block where the fridge gets its power. All the components are connected in series. When the On/Off switch if Off nothing happens. You want the switch Off if the rig not moving to conserve your house batteries. When the switch is On, the thermostat controls whether or not the fan will run. When the chimney is hot, the thermostat closes its contacts and runs the fan. Unfortunately, I cannot tell you exactly what temperature the thermostat is spec'ed to close at. The thermostat keeps the fan from running when the fridge itself Off or when the gas or electric heaters haven't run for a sufficiently long time. This too keeps the house battery from being drained even if the On/Off switch is On. In the pictures, yellow wiring was used at the thermostat and back of switch. The red wiring, the other thermostat, and the sheet metal the switch is mounted on are part of the Dometic "fix". Also, don't be confused by the dark cable entering the fridge chimney. That's a roof mounted cell phone antenna cable entering the rig.Alex Rutchka, SE #4 '05 MB
Re: Another Reefer Question Reply #17 – July 21, 2010, 01:39:35 pm Yahoo Message Number: 114658Alex; Thanks for taking the time to shoot some pics and to have them posted. Much appreciated. The consensus of opinion on this site and the two reefer techs I talked to points to lack of airflow over the cooling coil. One tech recommended the exact same fan setup you have on yours.Andy; You have a good point. At 60 mph one wouldn't think such a small fan would provide enough draft to do any good, yet it works for Alex. I'm going to try one other idea before I go the fan route and that is to jerry rig something like what most semi's have to deflect airflow over the trailer. That deflection screen on the top of most cabs. Not sure yet what I'm going to do, but thought this might be an easier and cheaper "fix" to the problem. It would seem logical that the airflow coming from the front of the rig and hitting the reefer chimney is the culprit, causing negative pressure or a downdraft. My thinking is deflect this airflow over and around the chimney vent and maybe the air will draft naturally. Worth a try I figure.I'll let all know what I find out.John 1994 22' Chug
Re: Another Reefer Question Reply #18 – July 31, 2010, 07:51:31 pm Yahoo Message Number: 114932I'm going to try one other idea before I go the fan route and that is to jerry rig something like what most semi's have to deflect airflow over the trailer. That deflection screen on the top of most cabs. Not sure yet what I'm going to do, but thought this might be an easier and cheaper "fix" to the problem. It would seem logical that the airflow coming from the front of the rig and hitting the reefer chimney is the culprit, causing negative pressure or a downdraft. My thinking is deflect this airflow over and around the chimney vent and maybe the air will draft naturally. Worth a try I figure.*Final report on results.* Drove my usual route, 19 miles up, 19 back, and freezer gained 2.5 F and the reefer gained 11.5 F in the first 29 miles. Decided to grab a roll of the all purpose gray fix-it tool [duct tape] and put two strips of tape across the very front of the chimney. Drove the next 9 miles and the freezer actually dropped a bit, and the reefer stayed constant. So this weekend I fired up the unit. Freezer started at 62.6 F. 38 miles. 1 hour 8 minutes. Freezer dropped to 45 F. Reefer was starting to drop. Conclusion. Alex was right. A downdraft was the cause of the problem. And what the unit must have been doing was trying to cool the outside because both the freezer and the reefer gained in temperature. Logic would say it would slowly warm like food in a cooler, but that wasn't happenning. The only explanation I can come up with was that the unit was drawing cool air out of the freezer and reefer and was trying to cool the outside air. Makes no sense, but what else could it be? Anyway. Fan works. Deflecting air away from the front of the chimney works. No matter what you do, you have to get an updraft working.John 1994 22' TK Chug
Re: Another Reefer Question Reply #19 – July 31, 2010, 08:06:56 pm Yahoo Message Number: 114933The fan should only be need when parked to ensure you have air rising up the chimney. When moving at hiway speed if you design the cap properly it will create negative pressure, just like the top side of an airplane wing, 80% of the lift is produced that way. This negative pressure should be more than enough to move enough air to cool the frig. coils. Try it and let us know the results. Doc, flying is one of my hobbies. FL2000
Re: Another Reefer Question Reply #20 – July 31, 2010, 10:59:29 pm Yahoo Message Number: 114941"The only explanation I can come up with was that the unit was drawing cool air out of the freezer and reefer and was trying to cool the outside air. Makes no sense, but what else could it be?" A refrigerator is just a heat pump that moves heat from inside the box to outside the box. If you block a water pump's outlet, it won't work... and if you prevent a refrigerator from getting rid of the heat it's trying to pump out, it won't work either. Anything that interferes with normal upward airflow over the coils in the vent stack will prevent the fridge from getting rid of heat, and thus will reduce or eliminate its ability to cool the interior of the box. Your test shows that when air blows downward from the top vent, that's what happens: the normal upward airflow is disrupted and cooling efficiency suffers. The answer, as has been said before, is to come up with a vent cover that creates a negative pressure (lift) at the top, and thus helps rather than hinders the airflow over those coils when driving. This could be a business opportunity, if someone wanted to take it on.Andy Baird http://www.andybaird.com/travels/
Re: Another Reefer Question Reply #21 – August 01, 2010, 01:43:00 am Yahoo Message Number: 114942From: Andy BairdThe answer, as has been said before, is to come up with a vent cover that creates a negative pressure (lift) at the top, and thus helps rather than hinders the airflow over those coils when driving. This could be a business opportunity, if someone wanted to take it on.Andy Baird Should ought'a be fairly easy to quantify without fancy test equipment. Just run a tube into the top of the vent connected to a manometer in the cab. Do a test run. Install fairing over front of vent, repeat test run etc. I know the flow over the roof in far from laminar. Probably all kinds of vortices and turbulence. It's probably that the various wave lengths of the turbulence and rotors change substantially with speed and this may render a given fairing or cap effective only within a narrow air speed range. It could be that a fairing that's effective at creating a vacuum in the fridge vent at one speed could increase pressure and reduce cooling when at a different speed. When I first installed solar panels on Yonder, I made a fairing to smooth the flow over the square leading edge of the front panel. The fairing was fixed to the roof and leaned back against the top of the solar panel. Should have been pretty straight forward but instead It buzzed like crazy around 65 mph. Took awhile to figure that out.bumper[Non-text portions of this message have been removed]
Re: Another Reefer Question Reply #22 – August 01, 2010, 07:48:28 am Yahoo Message Number: 114947It may be fairly easy to just try one of those RV-360 type rotating wind-vane sewer vent caps.....ideally a vent cap would include an adjustable spring-loaded offset plate like a carburetor throttle or choke plate, which would throttle the airflow as airflow increased.
Re: Another Reefer Question Reply #23 – August 01, 2010, 12:43:41 pm Yahoo Message Number: 114949"It may be fairly easy to just try one of those RV-360 type rotating wind-vane sewer vent caps" I dunno, Terry--a vent cap designed for a 2" diameter round hole doesn't sound like a very good match to a roughly 4" x 15" rectangular opening. And the RV-360's swivel action would be redundant, since the wind is always going to blow in the same direction when driving. There's probably some simple wedge-like shape that would produce the desired negative pressure at the top of the vent opening; it's just a question of finding it... and Bumper has explained how to do that with a simple water-tube manometer. Once an optimum shape is determined, find a company that can vacuum-form the things in quantity, and you've got yourself a business. Or license the design to Camco; they're all set up to produce items like this, since from a manufacturing standpoint it would be just like a small vent hood. Just be sure to use UV-resistant plastic. :-)Andy Baird http://www.andybaird.com/travels/
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