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Ask Dave: What can I do about fluctuating fridge temperature?

Answers to questions about RV Repair and Maintenance from RV expert Dave Solberg, author of the “RV Handbook” and the managing editor of the RV Repair Club. This column appears Monday through Saturday in the RV Travel and RV Daily Tips newsletters. (Sign up for an email reminder for each new issue if you do not already receive one.) Today Dave discusses fluctuating fridge temperature.

Dear Dave,
My refrigerator has fluctuating temperatures. What should I look for?  —Jeff

Dear Jeff,
If you have fluctuating temperatures in your refrigerator, I would start by checking it in both LP and 120-volt modes. This will verify if does it with both modes, or if it’s a specific issue with either the LP or 120-volt operation. Does this happen when you are plugged in or dry camping? Also, what is the ambient temperature outside? There are so many things that could cause this, so it’s important to verify all operations and document conditions.

First thing to do

The first thing I would do is connect a battery booster to the house batteries. The 12-volt house power runs the monitor board so check the thermostat, on/off, and cooling level. If the batteries are sulfated, they will seem to be charged at 12.6 volts but drop fast. So the unit might start up but could shut off after the batteries drop even if you are connected to shore power. That’s because the converter goes into trickle charge once the batteries hit 12.6 and don’t come on again for awhile. This will verify it’s not a drop in battery power.

Check the thermistor

Next, if it happens on both modes, I would check the thermistor. That is the temperature sensor located inside the refrigerator on the condenser fins. Check to make sure it is not covered in ice or frost. Position it higher on the fin so it senses more of the warm air that will rise to the top. It’s a good idea to place a small fan inside the refrigerator to move air around. I would also check the thermistor with a multimeter to verify it is working properly. Place the tip in a cup of ice water, which should bring it down to about 34 degrees and check the Ohm reading. There should be a plug connector along the wire that you can separate and get a reading. This procedure should be in your refrigerator owner’s manual.

If all this is OK, check your door gasket, as the door might not be sealing properly. Heavy items in the door while traveling can make it settle some and not seal properly. That means warm, moist air can get inside. Use a dollar bill between the door and gasket and shut the door. Give it a light tug and if it slides out easily, you need to adjust the door or get a new gasket. Do this on the top, bottom, and sides.

Check the roof vent

Refrigerators that are not mounted in a slide room have an open cavity behind the unit for heat to make its way up and out the roof vent, as pictured above. This vent is a rectangular flue that comes out of the roof with a protective screen covering it and a fiberglass top cover. This screen can get clogged with dust, leaves, and other items and can keep the heat inside the cavity. That will heat the refrigerator to abnormal temperatures and fight the cooling effect.

You should inspect and clean this vent periodically and make sure the cavity is open behind the refrigerator. It is not uncommon to find loose fill insulation stuffed in this area. This typically would not cause intermittent temperatures. However, your refrigerator may be running fine in the morning when it’s 50 degrees, but struggle when it gets to 80+ in the afternoon.

Check the cooling unit

The last step would be checking the cooling unit to see if it’s blocked. This can only be done by removing the refrigerator from the compartment and conducting a 24-hour cooling test. This is done by connecting a 120-volt power cord directly to the heating unit and let it run for 24 hours. Then check the inside temperature, which should be 34 degrees, and checking the cooling unit, which can get as hot as 300 degree at the evaporator tube.

If you have a blocked tube somewhere in the cooling unit, it will prevent the liquid and vapor from flowing normally and cause excessive heat in one specific area. You can typically see that on the tube as it has burned off the powdercoat paint and is rusty or discolored dramatically. You may also hear a gurgling sound. That means the liquid hit the blockage and is forced back down the supply tube, gurgling on the way down. In most cases, a blocked cooling unit means insufficient cooling. But it can be intermittent if it’s only partially blocked.

What if the fridge works fine on one mode and not the other?

LP mode

With all diagnostics of appliances that have multiply operations, it is important to isolate the functions and identify what works and what doesn’t, and with what variables, as discussed earlier. If the unit keeps consistent temperature on 120-volt power and not on LP, then we know there is an issue with the LP operation. More specifically, there is an issue with a consistent flame heating the rich solution which needs to turn to a vapor and start the journey. This could be a weak LP regulator, blocked LP supply line, or dirty burner assembly.

First inspect the flame inside the burner assembly. That can be accessed by the swiveling cover seen in the above photo. The flame should be a steady blue flame. If it is dancing around and has yellow or orange spikes, either the pressure regulator is going bad, or there is blockage in the orifice. This you can clean out with compressed air and a hose.

If this does not fix the problem, you will need to have a technician verify the regulator and LP pressure, which they can do with a water column tester.

120-volt mode

Intermittent temperatures just on the 120-volt mode typically mean a weak heating element. Instead of a flame, a heating element heats the rich solution and is on the side of the burner assembly. This can be tested using a multimeter and checking resistance.

Read more from Dave here

Dave Solberg worked at Winnebago for 15 years developing the dealer training program, as marketing manager, and conducting shows. As the owner of Passport Media Creations, Dave has developed several RV dealer training programs, the RV Safety Training program for The Recreation Vehicle Safety and Education Foundation, and the accredited RV Driving Safety program being conducted at rallies and shows around the country. Dave is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.

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Pierre Woody
17 days ago

Dave…..you didn’t give us the expected ohm readings, minimum and maximum, Thanks

Chris Mead
18 days ago

Should have mentioned sun exposure. My fridge runs 33-36 normally but if exposed to the sun can go up to 40. Goes back down though. I have the roof vent (not plugged) and of course it’s an absorption unit.

Kenneth Fuller
18 days ago

My friend has a 2006 Monoco where his refrigerator would never cool properly in warm/hot weather. After completing many tests, we went up on his roof to check his roof vent. Guess what? Monoco never cut the hole in the roof for his roof vent, but just put the roof vent cover on!