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Andonso's avatar
Andonso
Explorer
Apr 08, 2018

Protecting absorption refrigerators PCB

The last few years during the storm season I've been having issues with my refrigerator (Norcold N641) not working temporarily.

At first I thought there was something wrong with the PCB as the frig would all of sudden stop running and not turn on.

However this problem would only occur during a rain storm with higher than normal wind.

The problem has been occuring once or twice a year during the fall or early spring when we would get a few rain storms with wind.

After further inspection I found the PCB was getting wet. It appeared rain would enter the frig vent due to higher than normal wind.

Not much, but it seemed enough that additional moisture effected the pcb and wiring inside and the frig would just turn off and would not turn back on.

I inspected the rear of the cooking and there was both AC and DC going to the frig.

At first I thought I would need to replace the PCB, but after allowing everything to dry out the frig would start to operate normally again.

This problem occurred again last night so to be safe I moved all the food from the N641 to another frig inside of a cargo trailer.

The PCB cover currently isn't bolted down but fits tight around the PCB. I'm looking into trying to add additional protection to the PCB and other wiring going to and from the PCB because I'm not certain exactly where the problem with moisture exist.

I guess it's possible there's something wrong with the PCB and/or wiring however the problem in the past has only occurred during a rain storm.

I'm thinking perhaps of getting a backup PCB as Norcold has a new PCB that can be found new for under a hundred dollars that fits many of the Norcold units including the N641. The original PCB runs around ~$200.00 new.

The other thing I'm thinking of doing is to coat the PCB with an coating designed specifically for electrical circuit boards.

One type is called Conformal Coating that comes in different versions, usually in a 2 oz bottle with brush.

MG Chemicals Silicone Modified Conformal Coating 55 ml Glass Bottle w/ Brush Cap

Another one I found is "CRC Urethane Seal Coat Viscous Liquid Coating", 250 Degree F Maximum Temperature that comes in a 11 oz spray can.

Once applied both types are suppose to keep the circuit board dry and help protect it from moisture, water, dirt, dust, etc.

I haven't tired using either type yet and recently ordered some of the CRC in the 11 oz. spray can.

Anyway I'm going to try and build some sort of water shield for the PCB apply the coating.
  • 77rollalong wrote:
    there is electronics cleaners i have used that work quite well , i kinda surprised the board is not coated with some sort of epoxy thought, the contacts for the connections could be coated with a dielectric grease to keep moisture out .


    No the PCB isn't coated with anything, the board material with holes that the circuits are attached to yes, it's covered in some thin lacquer type substance.

    I have some CRC electrical cleaner, perhaps there are better ones?

    Using dielectric grease directly on circuit board isn't a good idea. On electrical contact yes, but directly on circuit boards, No. Even though dielectric grease is an insulator it doesn't insulate one hundred percent so any sensitive circuits might be effected as there is small amounts of conductivity. Also dielectric grease tends to attract dust and small particles some of which can be made from metal.

    A conformal coating on the other hand is designed to be applied to circuit boards and there are different types and thicknesses that can be applied as some circuits may require certain amount of thermal transfer such as heat sinks, etc.

    https://www.electrolube.com/technical-articles/conformal-coating-of-printed-circuit-boards/


    Below is a pic of a similar pcb for my Norcold. Under the 16-pin plug there's some slight corrosion I haven't yet been able to clean off and also some of the chip pins soldered through the boards holes still have some leftover of corrosion.

    If applying a conformal coating you want to try to get the board 100 percent clean, any leftover residue, rust, corrosion, mold, mildew, will become trapped by the conformal coating and potentially can effect the circuits.

    Pointer to image
  • there is electronics cleaners i have used that work quite well , i kinda surprised the board is not coated with some sort of epoxy thought, the contacts for the connections could be coated with a dielectric grease to keep moisture out .
  • After removing the PCB I'm finding green mold on some of the chip legs and a some near the 16-pin plugin.

    I'm not certain the best approach of removing the green mold which seems to be stuck to some of the chip legs solder into the pcb.

    I think what may have happened is the pcb became laden with moisture so many times a year over many years (10+) where green mold/mildew developed.

    The RV is kept most of the time in a climate with an average annual precipitation of approx 70 inches. The climate much of the year has around 80 percent humidity.

    I thought I had cleaned off any green mold and mildew however I guess not good enough as it seems just enough has stayed on the electrical contact posts which reacts to any moisture surrounding the pcb. The PCB cover isn't air tight so any moisture in the air may effect the pcb with even small amounts of green mold/mildew which is essentially a very fine corrosion.

    Overtime the mildew keeps building up even if there's no water that comes in direct contact with the pcb. During a heavy rain storm the humidity increases to 90+ percent and the pcb with even small amounts of fine mildew chemically reacts to excessive humidity.

    I've removed the PCB but it may be difficult to completely remove the green mold/mildew (corrosion) that become attached to some of the chips legs soldered into the PCB. I've tried using some electronic contact spray and a toothbrush. However I'm not certain how well that working.

    I probably need to soak the pcb in a solution that will neutralize the mold and fine corrosion without effecting the pcb and it's electronics.

    Perhaps a naval jelly? Which essentially is phosphoric acid that turns the mold & corrosion into iron phosphate which then can be flushed away with some electronics spray?

    So essentially I think the pcb even though protected somewhat from direct contact with water is reacting to higher humidity over many years enough that small amounts of corrosion (green mold) develops.

    Once I'm able to totally clean the pcb and apply a coat of Conformal Coating should help prevent the corrosion (green mold) from developing in the future.
  • ScottG wrote:
    Better to protect the PCB from getting wet at all.


    Yeah but I can't choose the weather. I'm next to the Pacific Ocean winds can typically get to be around 40 to 60 mph. A number of years ago there was a storm and the winds got up to 120 mph flip over a few 5th wheels I guess weren't tied down good enough

    I'm planning on sealing the cover perhaps with some sort of silicon. I'm not certain the existing pcb cover is good enough if ~50+ mph winds are going in all directions up, down, sideways, underneath and over the top of the RV I think the rain is being forced through the frig vent and ends up effecting the PCB.

    I was thinking of installing some sort of cover over the vent but I'm not always around the RV to remove a cover when unneeded. Absorption frigs need to be level and won't operate correctly without enough air flow.

    I looked around for an electric but all are either too small or too large. The frig is mounted off the floor near a wheel well so it would be impossible to somehow mount one on the floor.
    Anyway I'll try to devise a internal cover over the existing pcb cover that won't restrict air flow.

    The PCB, even a small amount of water or moisture can prevent them from working. I was hoping as an added protection the conformal coating will prevent problems in case the PCB become wet again. However I'm uncertain how well a coating would work to protect the PCB plugs contacts and wires.

    Currently the frig won't turn on as I can see a very small amount of some moisture one to two drips from the bottom. It appears moisture somehow got inside onto the other side of the PCB between the PCB and what it's mounted to.

    I'm hoping it will start working again once the weather gets better and it has a chance to dry out.

    I think absorption frigs are great for traveling but they can potentially become a nuisance for full timing and cost more to run than an electric.
  • The CRC Uerathane Seal Coat description shows

    Electrical & Electonic insulator, Flexible, non-conductive polyurethane film

    So I guess it's considered to be a polyurethane film. I'm uncertain why it's labeled Uerathane as there are differences between the two. Such as e.g. a polyurethane takes longer to dry than a urethane.

    Anyway I would want a product that's been tested specifically to use with electronic circuit boards and comes with a temperature rating.

    Silicon based Conformal coatings have a higher (and perhaps lower) temperature ratings than urethane/ polyurethane coatings , which usually have better resistance to various types of chemicals.

    So if an area has high temperatures or the circuity reaches higher temps above ~250 F probably a Silicon based Conformal Coating would most likely be a better choice.

    The absorption refrigerator's cooling unit I don't think would ever reach 250 deg F. so a Urethane/Polyurethane coating should work just fine.

    I guess for some applications a coatings thickness can become an issue so one type may be better than another for more specific applications. I remember reading somewhere there are basically 5 types of conformal coatings which includes Urethane/polyurethane.
  • Regular polyurethane spray works well as a conformal coating.
    One of the companies I worked for used it. One advantage was that you could easily repair the board because it was easy to do. The coating went away from the joint when you applied a soldering iron to it.