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Is Your RV Refrigerator Cooling Properly in Hot Weather?

Is Your RV Refrigerator Cooling Properly in Hot Weather?


avatar   Scott
Trip Date 10/04/2020
Posted On 10/19/2020 09:10:09

United States | Camping | RV | Hack | Repair | Norcold | Refrigerator | Fridge | Hot Weather | Refrigerator Not Cooling | Warm Fridge | Freezer is Frozen | Ventilation | Thermistor | How to Install Fans to Keep an RV Refrigerator Cool | DIY



Have you ever noticed that your freezer is frozen but your RV refrigerator is not cooling - especially in hot weather?

While camping during mid-summer between Texas and South Dakota, we noticed that our Norcold refrigerator was not as cold as normal. We thought that something had frozen-up in the back of the freezer which was preventing the fridge from getting cold enough (even though the freezer was still freezing). We unloaded everything into an ice chest and turned it off. We waited until it was warm and fully defrosted before restarting it. Only when the temperature inside the refrigerator was back near 33 degrees, did we reload it. It seemed to work fine again - but, as we traveled north the outdoor temperatures were also cooler.

About two months later when we were headed in our RV to the southwest US, it happened again. Hmmm ... what was going on?

The ambient outdoor temperatures were consistently in the 90's and 100's on both occasions. The freezer seemed to be working fine, however we definitely had a warm fridge - the refrigerator temperature had climbed up to between 45 and 52 degrees.


Inside Fridge Temperature with Wireless Thermometer

Inside Fridge Temperature with Wireless Thermometer

If you've ever had a similar experience, the good news is that there's a DIY repair (hack) that will make a big difference in your refrigerator temperature. In this article, you'll find some background information on how RV refrigerators operate. In addition to understanding the importance of ventilation and circulation, you will also learn about the thermistor. Finally, I'll share the exact steps that I took so that you too will know how to install fans to keep an RV refrigerator cool.

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Research on RV Refrigerators Not Cooling Properly

Trying to determine the problem, I spent lots of time doing research on the web. Here's a summary of what I learned:

Evaporator Refrigerators

The refrigerators in many RVs are evaporator refrigerators which operate differently than the compressor refrigerators standard in most homes. I'll start with a very brief overview of the thermodynamic theory of evaporator refrigerators. A mixture of ammonia and water is heated (either electrically or from propane). As the vapors rise, they expand and get cold. The cold vapors go through the freezer fins, fall through the refrigerator fins and naturally condense back to liquid to be recycled again. If there is too much heat at the top of the unit, it can't get cold enough. The fins in the freezer and fridge are designed to allow the hot energy to pass out of the refrigerator cabinets while the cold passes into the cabinets.

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Thermistor

On Norcold models, a thermistor (thermostat resister) is clipped onto the fins and connected to the light assembly inside the fridge. The thermistor senses the temperature of the fins and electronically creates resistance that the refrigerator controller board understands.


Norcold Thermistor Part

Norcold Thermistor Part

The thermistor can easily be disconnected (by detaching the white connector) to determine if it is working correctly. When detached and with the refrigerator set on its coldest setting, it should cool off at its maximum rate (and even possibly drop below 32 degrees, or freezing).

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Ventilation and Circulation

I came across discussions about the need for circulation inside RV refrigerators. If overloaded, RV refrigerators will not cool properly.

An auxiliary fan on the inside is needed if there is too much frost build-up on the fins. Frost build-up prevents cold air from circulating around the inside cabinet. This can happen in colder or humid weather, or if the door is opened too frequently. Some people add fans inside the refrigerator to keep cold air circulating (and to keep the fins from freezing).

I also learned that the outside rear of the refrigerator needs good ventilation. If the rear of the fridge is too warm (or if it is too warm outside), the refrigerator won't cool properly. Heat from the rear will migrate inside an RV refrigerator. An auxiliary fan on the rear of the fridge is needed if hot air from the refrigerator can't escape. This is often a problem when outdoor temperatures are hot (90 degrees & up).

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Level Parking

Another big factor in having RV refrigerators work correctly is that the RV has to be level. We have traveled in our RV for over 3 years. During that time, we've parked in many different locations and haven't experienced a warm fridge issue before.

We do level the RV front to back using the power hitch jack which is fairly easy. Leveling side to side, however, is more work and we usually don't bother with that. My research indicated that generally, if the bed feels level, it is level enough. (With refrigerators on the side of an RV, if the RV is within 3 degrees of level front to back, and within 6 degrees of level from side to side, it should work fine.)

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Our Set-up and My Experiments

Ideally, RV refrigerators are installed with an intake vent on the bottom rear and a vent on the roof which lets hot air escape. Some RV refrigerators have ventilation fans in the rear and others do not.

We have a basic Norcold N811F RV evaporator refrigerator which, unfortunately, is mounted in a slide. I could not see a fan on our refrigerator, but at times I could hear one. We do have a vent on the outer side of the slide near the top. This vent is partially covered by a board mounted by the RV manufacturer on the rear of the fridge. Because of this, only two of the three small vent slots allow air to escape.


Vent Cover has Small Openings

Vent Cover has Small Openings

Hot air gets trapped in the cabinet behind the refrigerator which causes overheating. It seems that the purpose of the board is to provide insulation between the outside skin of the RV and the refrigerator cooling components. As it goes up as high as the fins, it also provides an air channel from the lower vent to the upper vent.


Top Rear RV Refrigerator Vent

Top Rear RV Refrigerator Vent

Over the course of several days, I tried three different experiments in an attempt to determine which had the best effect on cooling the refrigerator. I used a wireless thermometer and placed the outdoor sensor unit inside the fridge for easy monitoring of the temperature:

  • I placed an 8" DC fan inside the refrigerator;
  • I hung an AC fan on the outside of the RV; and
  • I also unplugged the thermistor.

After several days, I determined that I needed more ventilation on the outside rear of the refrigerator in order to keep it cool - especially in hot weather and when direct sunlight is beating on the side of the RV.

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Shopping for Parts

In order to find the parts that I needed, I first searched online. I didn't want to wait for the arrival of an online order since we were staying in Mesa, Arizona (where the outside temperature was expected to be over 100 degrees every day during our week long stay). Once I knew what I wanted, I headed out to several nearby stores:

12v Fans

Once I began shopping, I found many fans designed for the inside of the fridge, but none for the outside. The issue is that one size does not fit all. The space available in the rear of the fridge and the positioning of the vents is different on all refrigerators. Additionally, mounting fans can be challenging!

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There are 12v fans available from campingworld.com and etrailer.com that are intended to provide extra ventilation in RV refrigerators. However, these fans can cost as much as $50.00 each. Since I wanted to install several fans, I was looking for a less expensive alternative.

These 12v fans are essentially the same type of fan that is used in a computer chassis cabinet to keep a computer cool. Frys.com offered "computer fans" that were much cheaper. What I found at the nearby Fry's Electronics was a box of four 12v fans priced at only $8.00 - wow what a deal!


CPU Case Fans

CPU Case Fans

The fans that I purchased were square and measured 80mm per side (about 3 inches). They are advertised to move 26 cubic feet of air per minute. (Any size fan is fine, as long as it will ventilate the refrigerator cabinet.)

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My goal was to install 3 or 4 fans, all mounted in a row. The issue is that there needs to be enough space above the rear exterior fins to mount the fans. You have to get creative and visualize what size fans will fit and also where the fans can be mounted. After taking measurements, I determined that I could only use 3 fans since the vent door latches interfered with the space needed to add a fourth fan.


Array of Fans

Array of Fans

The fans that I purchased had 3 pin connectors. (Other fans may have only 2 wires, and some may have 4 wires.) To enable the fans to run, you only need two wires. I had to determine which two wires drove the fans and which was the unneeded control wire that senses the fan speed.


Figure Out Which Wires Drive Fan

Figure Out Which Wires Drive Fan

Wiring

Since the amperage of the fans is very low, almost any paired stranded wiring will work. I paid about $12.00 for a much longer than needed length of wiring.

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Switch

I wanted to have a switch on the inside of our RV so that we could turn the fans off when they were not needed. (In warm weather, we just keep them running all of the time.) The switch that I purchased was only about $3.00.

Since the fans are very quiet, it is hard to determine whether they are turned on when we are inside the RV. We've had to learn to listen for the faint vibration sound. If I were to do this over again, I would purchase a switch with an LED light so that I could easily see if the fans were turned on or off.)

Additional Needed Supplies

Here's a list of the additional supplies that I either purchased or already had in my traveling tool bag:
  • Zip-ties
  • Plumber's tape
  • Electrical tape
  • Gorilla tape
  • Plastic corrugated signboard
  • Twist connectors
  • Nuts and bolts

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Planning and Mounting the Fans

Once I had all of the parts that I needed, the real work began:

Finalizing a Plan

After visualizing where the fans can be mounted, the next step is to determine whether you should mount them inside the RV cabinet or on the vent panel door itself. (Think of your stove fan or bathroom fan. They both suck the air and have a tube that takes the hot air outside. That is what you want for your refrigerator as well.)

One example that I saw had fans simply mounted above the external fins (not in any way connected to the vent panel door and without an exhaust channel). This option has both a pro and con. By mounting the fans inside the cabinet at the top, it allows the door to be opened without issue. On the other hand, the air may circulate within the cabinet and not exhaust outside very efficiently.

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I decided to mount the fans to the vent panel inside a housing that would force the air outside. I had to carefully position the fans so that, when the vent panel is closed, the fans would fit perfectly into the available 4 inch space above the external fins.


Back Of Vent Cover

Back Of Vent Cover

Attaching the Vent Door

As I built the fan assembly, I added a zip-tie mechanism that would allow the vent door to hang on the outside of the RV. I put loops on the board installed by the manufacturer and also on the edge of the vent door in order to connect them together. This allows the vent door to remain attached to the RV while open.


Install Zip-Tie Hangers

Install Zip-Tie Hangers

Zip-Tie Loops On Vent Cover

Zip-Tie Loops On Vent Cover

Hangers from Zip-Ties

Hangers from Zip-Ties

Mounting the Fans

I used plumber's tape (flexible metal straps) to build a mounting bracket. I then mounted the fans on the bracket. (In order to align the predrilled holes on the bracket with the mounting holes on the fan, I had to put a small crimp in the strip between fans to avoid a big gap.)


Build Bracket with Plumber's Tape Strapping

Build Bracket with Plumber's Tape Strapping

Fabricate and Mount Custom-Size Brackets

Fabricate and Mount Custom-Size Brackets

Before mounting them, I connected the fans in parallel so that each fan runs on 12 volts. (If one fan fails, the others will continue to run.) I connected the three fans together with a short wire stub serving as the main connection point. I just twisted all of the wire connections with electrical tape and Gorilla Tape. This created a compound fan module that could be connected to power later.


Mount Fans

Mount Fans

Connect All Wires in Parallel

Connect All Wires in Parallel

Connect a Single Connector Stub

Connect a Single Connector Stub

Building Exhaust Enclosure

Once the fans were mounted, I built an exhaust enclosure so that the hot air that is sucked out would be forced to go out of the vents in the door. To build the housing, I used plastic corrugated sign board that I found at Home Depot. I simply cut pieces of the sign board and taped them into the proper position with Gorilla Tape.


Plastic Corrugated Sign Board

Plastic Corrugated Sign Board

Build Enclosure for Exhaust Fans

Build Enclosure for Exhaust Fans

Side of Enclosure

Side of Enclosure

Before hanging the vent panel door with the mounted fans on the outside of the RV, I inspected and tested the fans.


Attach Vent with Fan Assembly

Attach Vent with Fan Assembly

Inspect Fans

Inspect Fans

Wiring the Fans

Two paired wires are involved in connecting the fan assembly. The speaker wire that I used worked great, but it is not black/red color coded.

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Before beginning, it is prudent to disconnect all AC and DC power before adding any additional wiring. If you are unsure about the wiring, check with an electrical expert.

I first measured a length of wire and connected a switch to one end. I ran the wire from the inside of the RV above the refrigerator through the small space that leads to the back of the fridge. This allows us to turn the fans on and off from inside the RV. (I used a twist switch with simple wire connectors. As I mentioned earlier, I wish that I had purchased a switch with an LED light so that I can easily see if the fans are turned on or off.)


Switch Accessible Inside Above Refrigerator

Switch Accessible Inside Above Refrigerator

Next, I measured a length of wire to fit between the fans and the 12v power connection point at the bottom of the rear refrigerator cabinet. After connecting the fans with twist connectors, I taped the wires to the wall along the side of the rear cabinet so that they wouldn't interfere with anything.

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I connected the fans and the switch into a single circuit by connecting one of the paired fan wires to one of the paired switch wires. I then connected the remaining switch wire and the remaining fan wire to the 12v power source behind the refrigerator. Once you make a connection, make sure that the fans blow in the desired direction. (In the photo, you'll see my wire connected to the 12v power source and the ground connection of the black controller box for the refrigerator. It was clearly marked as 12 volts.)


Connect Fans to 12v in Back

Connect Fans to 12v in Back

Cooling Results

After wiring it all together and closing the vent door, I turned on the fans and just let them run. The fans ventilate the rear of the fridge cabinet by sucking cool air in from the bottom vent (which flows up through the cabinet and through the fins) and then pushes the hot air outside through the upper door vents. The fans have definitely helped to keep our fridge cooler - but still not as cold as when camping in cool weather locations.

The intended operating temperature of an RV fridge is 33-40 degrees. (Before installing the fans, the temperature inside of our refrigerator was hitting 40+ degrees when the outdoor temperatures were 90+ degrees.) With the refrigerator set on 5 (the coldest setting), since installing the fans, our refrigerator temperatures have remained in the 30's (31-39 degrees) when in 100 degree weather. At least, the temperatures are no longer going into the 40s and higher!

For the past three years, we had typically kept our fridge on setting 4 (out of 5). During the hottest part of the day when temperatures are exceeding 93 degrees hour after hour, we have found that we need to keep our refrigerator on setting 5. On days when the outside temperature is 93 degrees or less, the setting of 4 still seems adequate.

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Since installing the fans, I've also experimented with the positioning of the thermistor. I read that moving the thermistor further to the left should result in a lower target temperature, while moving it right raises the target. The actual number of degrees is uncertain, and Norcold actually says that this is not a proper fix. (Norcold states that the thermistor should stay connected at the designated place depending on your refrigerator model.)


Installed Thermistor

Installed Thermistor

More RV Refrigerator Tips

Have you ever noticed that your RV refrigerator light is blinking? Check out our article, "What to do when your RV Refrigerator Light is Blinking" to learn why this might be happening, and also what to do!

Refrigerator Temperatures

What experiences have you had with ensuring that your RV fridge remains cold, even when camping in very hot weather?
Is Your RV Refrigerator Cooling Properly in Hot Weather?







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