By Paul Unmack, PE-CSE, ME #116483, www.arprv.com
My previous series of articles discussed the process of how refrigeration works. In addition, I’ve discussed how to improve the reliability, efficiency and safety of RV refrigerators. The last article discussed venting and methods to improve refrigerator efficiency, by using a fan controller like the ARP + Fan Control. This article will cover the inside of the refrigerator and issues that can affect the contents.
One of the most common problems with the refrigerated cabinet is the door seals. Faulty seals can result in problems, such as excess frost and moisture and poor cooling performance in the cabinet’s interior. All of this adds up to efficiency issues. Ambient air getting into your refrigerator results in excess frost buildup. This is due to the moisture in the air freezing on the cooling fins located at the back of the refrigerator. The frost insulates the cooling unit from the inside of the refrigerated cabinet, preventing the unit from doing its job. The ambient air moisture can also cause the contents to become damp, resulting in accelerated spoilage and sogginess of some types of food. Storing wet items in closed containers will help to keep moisture out of the refrigerated compartment.
Testing Seals for Leakage
Most folks have heard of, or used, the dollar-bill test. This is done by shutting the refrigerator door with a dollar bill stuck between the door and the seal. Once the door is closed, pull the bill out to see if there is resistance. If there is little resistance, it’s likely the door doesn’t have a tight seal. This can cause air leakage, allowing hot air and moisture into the refrigerator.
Another variation of this test is to put a bright light into the refrigerator and, in the dark, look around the seal to see if light is coming through.
All refrigerator seals can be replaced, but some OEM seals may not be available for your make and model. Because your appliance should last for the life of your RV, this presents a dilemma. Your options are to replace the refrigerator or the doors, get handy and resolve the problem yourself or have a technician fix the door seals.
One of the first steps to replacement is to identify which type of seal you need. There are two types: magnetic and nonmagnetic.
If the door seals are the magnetic type, there are universal refrigerator door seal replacement kits available. The issue is in obtaining a kit that works. The thickness of the seal must be exact and able to compress correctly when it is functioning. You can get an idea of the thickness by measuring your existing door seal; however, a used door seal will be more compressed. In most cases, the replacement needs to be a little thicker than the measurement of the used seal to compensate for the required thickness.
Magnetic door seals can be replaced with nonmagnetic seals if you latch your door. RV refrigerators require that the door be latched so that they do not open during travel. Using the door latch every time you get in and out of the refrigerator can be a hassle, but it can be better than buying a new refrigerator if magnetic door seals cannot easily be replaced.
Nonmagnetic door seals are easy to replace. All you need to do is find a closed-cell foam that is thick enough to fill the gap and can be compressed to form a tight seal. Online I searched “D-type extra thick seal” and came up with a number of brands that will work. The D-type seal refers to the cross section of the seal. At the end of the seal, there is a hollow D-shaped section that makes it thick but allows a lot of compression. This configuration is perfect for retrofitting new door seals on your refrigerator.
After you purchase the seal, cut it to the correct size and glue it on. I have used 3-M weatherstrip adhesive for over 40 years and it works. If you don’t already have weatherstrip adhesive, keep some in your RV. You will use it sooner or later to fix a seal or weatherstripping.
Frost and Fans
In the May/June article, I discussed RV refrigerator ventilation and the fact that having a fan controller (such as the one found on the ARP + Fan Control, see page 29) will improve cooling-unit efficiency. Another benefit to having a fan controller that only turns on the fans when refrigerant is being produced, is that it can help to prevent frost buildup. If fans are installed inside the refrigerator without a fan controller, they will run continually, even when they are not needed.
Fans circulate and distribute cool air within the refrigerated cabinet, so it’s important to avoid overfilling its contents. If food is tightly packed into the refrigerator without ample space between the items, limited circulation will result in poor cooling performance. Make sure there is an open channel between the top and bottom when placing items in the refrigerator.
One of our customers came up with a great solution to this problem. They mounted two PVC tubes at the back of the refrigerator that provided a channel for air movement. The tubes were at opposite corners, with one tube having a fan sucking air out and blowing it to the top of the refrigerator. The other tube was the return tube with no fan. This allowed the refrigerator to be packed without blocking the necessary air circulation for proper cooling of perishables.
Similar to stocking the refrigerator, the freezer section needs to be stocked with spaces between the items to allow freezing of all the food. Freezing occurs only at the back of the freezer. The evaporator is the part of the cooling unit that performs the actual cooling inside both the refrigerator and freezer compartments. The refrigerator has cooling fins that are attached to the lower part of the evaporator and, as a result, it’s impossible to prevent cool air from entering the refrigerated compartment. Most RV freezers do not have cooling fins, so food can be packed up against the back wall of the freezer. The food packed against the back receives the majority of the refrigeration effect, and the items at the front never freeze.
My wife and I have a small refrigerator, and we buy food in bulk; therefore, we have found ways to deal with this problem. The most obvious is to pack the freezer with already frozen food, but then items need to be rotated from front to back so the food at the front remains frozen.
The next method we use is to put food that needs to be frozen into the back of the freezer. After the food is frozen it can be moved to the front. If a lot of food is put into the freezer that needs to be frozen, you have to keep rotating the items so that they all freeze uniformly. For us, we have a routine of food rotation so we consume the food before it becomes old. The older goods are always moved to the front to be consumed first.
One big difference between your household refrigerator and your RV refrigerator is automatic defrosting. Most RV refrigerators don’t have automatic defrosting because they don’t have electrical resistance heaters to defrost the cooling fins. Your house has an abundance of power so it is simple and cost-effective to defrost in this manner. With limited power available to an RV, it is not practical to power automatic defrosters. Unfortunately, you need to manually defrost your RV refrigerator.
The procedure for defrosting is simple and you should start with an empty refrigerator. We’ve found that, with fans in our refrigerator, we can defrost it once a year, sometimes twice a year if we have humid weather. Once the quantity of food has been reduced, use the freezer to make ice to use in a cooler. We use blue ice. Put your perishables into a cooler, and then turn off the refrigerator and open the doors. (See Mark Nemeth’s Website at www.marxrv.com/hints.htm#Fridge for a method that uses a portable fan to speed up the defrosting process.) Or, if you have an ARP + Fan Control and you have a fan inside your refrigerator, you can turn on the fan manually.
Defrosting takes approximately one to two hours. Lay towels on the bottom of the refrigerator to soak up any water from the melting ice. Once it is defrosted and the inside is dry, restart the refrigerator and load when it begins to cool.
• Do not use heaters to melt the frost. The heat can also melt the plastic interior.
• Do not use sharp instruments that can damage or puncture the cooling unit. Allow ice to melt and then use your hands to remove large chunks.
Folks often comment that their refrigerator does not seem to be cooling well enough. This is a subjective statement since there are many areas within the refrigerator to measure temperature. In addition, the food stays colder than the internal air if the door has been opened frequently. For this reason, we try to promote the following standards for refrigerator and freezer measurement:
When measuring temperature within the refrigerated cabinet, the measurement probe should be at the same location as the refrigerator’s thermistor. This measurement location has two advantages; one is that you know the range of temperature within the refrigerator for diagnostics; the second is that you can compare temperatures with another make and model of refrigerator that is the same as yours.
For the freezer, we measure the temperature at the back of the cabinet simply because this location does not interfere with food storage. In addition, this location most directly measures the performance of the evaporator in the freezer section.
Loading the Doors
In conclusion, avoid loading the door shelves with heavy items while traveling. A gallon of milk weighs around eight pounds, and as you are banging down the road, this stresses the door and the hinges. When the door warps and the hinges fail, the door seal will not function properly.
Thanks for all of the great input we have received. If you have questions, comments or helpful tips for others regarding RV refrigerators, please contact us at www.ARPrv.com and select the “Contact Us” form. We are pleased to help with your refrigerator needs or to post your great solutions for refrigerator problems.
Note: If you repair your door seals, e-mail us at ARPrvSafe@gmail.com and send your make and model of refrigerator, photos, the type of seal you used and any special steps you took to retrofit seals. We at ARP want to help others keep their refrigerators running great.
Paul and Mao Unmack are mechanical engineers. Paul ran an automotive repair business in Red Lodge, Montana, for 20 years before receiving his engineering degree. He has practiced nuclear, fire suppression and industrial process control systems design. Mao designed pressure vessels for ammonia plants in China for 12 years, then came to the U.S. to get a master’s of welding engineering. She designed biodiesel plants and worked for a government-funded research and development organization. Paul and Mao run the entire ARP control business while taking on engineering consulting gigs.