Friday, January 7, 2011

Refrigerator



Reference Sources
http://rvmobile.com/Tech/Trouble/CoolingD.htm
The Dometic RM2662 Manual

General Operation
1. The first thing to remember is that RV refrigerators like to be level. Reasonably level is when the coach can be comfortably lived in with everything operating normally. This means no obvious slanting of the coach. Operating the refrigerator when parked and not level can permanently damage the cooling unit. Levelness is not a problem when traveling - the constant movement of the coach keeps the refrigerator working normally.

2. Using propane when traveling: opinions seem to be fairly evenly split on the wisdom and safety of traveling with the refrigerator operating on propane.
a. Should you feel safer with it off, the refrigerator will stay cold through the day provided you don't open it very often.
b. If you do travel with it on, please be sure to turn it off before pulling into a gas station to refuel. The open flame from the burner could ignite gas fumes.

Routine Maintenance
To ensure top performance of your refrigerator, be sure to annually clean the vent stack, the exterior coils and ensure the burner is operating cleanly. The stack and coils over time will accumulate dirt and webs. Compressed air will do be helpful for that.

The refrigerator's gas jet builds up a coating during use; that limits the amount of gas that flows. The cure is to remove the jet, soak it in solvent and then brush clean with an old tooth brush. Never use any type of metal wire to clean the jet as it will most like damage the jet.
See the references noted above for more details on how to properly accomplish these tasks.

When cleaning the interior of the fridge, you should clean the set of metal fins that sit at the upper back. Below these fins is a short removable shelf, which has a tube/vent that leads to the outside. This is where the condensation runs out of the fridge. This shelf is removable, and right where the tube attaches to the back of the fridge, there's a small catch cup; that cup may be full of goop and prevent the tray from draining properly.
Also, at least once a year, go outside and check where the fridge actually drains below the fridge. This opening has a small perforated cap and this can also get clogged with road grunge.

After cleaning both of these openings, blast a bit of canned air till the tube runs clear.

Trouble-Shooting

Won't start

Normally all you do is turn the refrigerator ON, and it selects the mode. If it sees 120VAC, that's what it'll use. If no 120VAC and if the engine isn't running, then LP. If no 120VAC AND engine running, then 12VDC.

Note: It calls for a charged 12VDC battery supply to be able to make these decisions and select a mode of operation. Battery weak or bad connections, fridge won't operate properly. There IS a "lockout mode" where it'll cool on LP if started on LP and battery power fails. It'll cool to below freezing or the LP runs out, whichever comes first.

Cools poorly when running on propane
According to information in "The RV Repair and Maintenance Manual", these are the probable causes of insufficient cooling when on LPG:
- Restricted air circulation over cooling unit.
- Refrigerator not level.
- Insufficient LP gas.
- Feeler point of thermocouple flame-failure device not heated enough by flame.
- Clogged bypass screw, clogged burner head, clogged burner-jet orifice.
- Flue baffle not inserted into central tube of cooling unit.
- Baffle too low in flue.
- Loose burner assembly.
- Improper thermostat setting.
- Failed cooling unit.
- The gas jet may need cleaning:

Remove the jet and wash it in alcohol (using a old toothbrush to scrub the inside of the jet) . Blow it out with compressed air and reinstall. Never use anything metallic ( wire for example) to clean the hole in the jet. This could alter the shape and size of the hole. This information should be in the owners manual. The flue may need occasional cleaning also.

The hard part of cleaning the jet is getting it out. I use a small wrench, from a set of 'ignition wrenches', bought at Sears, to unscrew and to replace the jets. Each model of refrigerator is a little different, so I cannot say what tool to use to remove yours.

- The thermocouple may need adjustment or replacement:
Looking closely at the spark during re-ignition, I saw that it was arcing to the tip of the thermocouple instead of the burner tube as it should have been. I replaced the thermocouple because the tip where the spark was hitting was badly corroded and I suspected damage to the thermocouple itself. Next, I adjusted the position of the mount of a new ignition probe so that the probe arced to slotted area on top of the burner tube. (I had to replace the original ignition probe because I snapped its tip off when I stupidly tried to bend the tip itself rather than adjust its base as required.) The check-light-on problem went away and the refrigerator has been working properly ever since.

Won’t operate on propane:
1. I replaced the circuit card and wiring harness with Dometic replacements and the problem has been fixed and has stayed that way. If I remember correctly, the circuit card cost me about $115 and the wiring harness $25. Dinosaur Electronics makes replacement boards for Dometic units. I've read some opinions that they're better than Dometic's with a longer warranty but don't have any personal experience with them. http://www.dinosaurelectronics.com/

2. When you have the cover off, at the right of the refrigerator compartment, you will see a small metal wire that is held over the burner. It has to be EXACTLY the right distance from the flame or it will not let the burner stay on. Try moving it a little closer or father away and see if that allows the refrigerator to stay on.

 
Won’t cool properly when underway:
The baffle that is on the top of the unit near the roof is an add-on to the baffle dometic uses. Its purpose is to prevent the blowout of the flame on the gas heater at the base of the cooling unit flue. Check to ensure your baffle is installed. Additionally, the placement of the fridge on an MB is such that an "air dam" is generated when you're moving at speed. This prevents easy flow of cooling air by the cooling coils/fins on the back of the fridge making the cooling unit less effective.

The solution may be to install a vent exhaust fan just under the roof vent cover. The fan is controlled by a thermostatic switch mounted on the chimney below where the electric heater is. The idea is to run the fan only when the chimney is hot. You can add an On/Off switch in series with the wiring so as to turn it all off and conserve the house battery when stationary or not moving on interstates.
Another possibility is a defective thermistor - a $15 part. 

Won’t operate on propane unless warmed up on AC first:
1. , The problem is probably a cracked ceramic rod surrounding the igniter wire. You can test this by removing the burner cover on the far right of the exterior refrigerator compartment, depressing the refrigerator start button, and immediately attempting to light the burner with a match. If the burner lights, let it run for a minute or so, and blow out the flame. If the igniter now (automatically) restarts the flame, then your problem is almost certainly a hairline crack in the ceramic rod, and the igniter should be replaced. Easy to do yourself, one screw and one connection. Take the old igniter with you (or the whole rig) to be sure you get the correct igniter. They come in many variations.

2. The easy way to do the test I am about to describe is to have the referigerator on, running on electricity. Standing at the service door of the referigerator, simply unplug the refer, and watch the ignition sequence, specifically the ignitor probe and the burner itself. Watch the sparking and make sure it is sparking to the burner and not some other metal surface. I have found several of the Dometics set incorrectly and the spark is not contacting the burner and when cold it will not start.

3. . If the thermo-couple is not in the right position the fridge will shut off after a few minutes and the indicator light will come on. Have someone turn the fridge on from inside the coach. You should be outside with the access panel removed. Use a pair of pliers or a standard head screwdriver to push the thermocouple closer to the flame. Be gentle when you bend it. After a few tries you should get it in the right position.

Fridge portion running too warm or cool
1. There in is a plastic piece (called a thermistor) on the back of the fridge hooked to a wire that runs up and down the coils on the back of the fridge. Push it up for a cooler temp and down for a warmer temperature. The plastic piece actually houses a thermistor used to regulate box temperature. Moving it up and down adjusts temperature. Here's a short article on the thermistor, with pictures.


Replacing the thermistor with third party item.

2. Low temps in the main refrigerator may be due to a dirty burner or low voltage (below 108 and you lose cooling power). That is why it is important to have that once a year check-up, and make sure they clean the burner assembly etc.
Dometic RM763: The fridge check light light will come on sometimes

Can you remove the roof vent over the fridge? If you can, you should see a wire rod hanging off the top of the stack. Stack is at the right hand side as you face the back of the fridge from outside the coach. Make a hook to pull that hook out. A sprial "deflector" should follow. Then work it up and down a few times. Knock on the stack with a screwdriver handle or something else you can reach it with. Put deflector back, hook the rod, reinstall the vent cover.

Then from the outside, you can remove the burner. It's held by a lock ring under the flame shield and maybe one more screw. Clean dirt (and all the rust that fell down!) from the burner area.

Retry the fridge. If it's still going into Check, then remove the burner assembly and flush the orifice "jewel" opening clean with alcohol and air blow it dry. Don't pass a wire through it, can distort/enlarge the precision opening.

Bins for freezer door: Here's a great way to save few bucks if you need new/extra bins for the freezer door.

Contributors: WxToad, Alex Rutchka, Larry Wade, Jim, Malcolm, Jonna Harlan, Joan Taylor, Mike Sylvester, Kurt, John Wozniak, Kate Klein, Don Malpas
Revised 22 Jul 2011

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