Cleaning OTR A/C evaporator

[MyPrevost]

I’m trying to address what seems to be inadequate airflow from the registers located at the bottom of the windows for the over-the-road A/C system.

When we purchased the bus, it didn’t have any air filters at the evaporator, and I can only imagine how long it operated without them. Given the significant amount of dirt accumulating on the filters we installed in such a short time, I suspect there’s likely dirt and other obstructions inside.

While I can see the front face that accommodates the filters, the back side is obscured as it’s situated against the heater core. The fins are also tightly spaced, making it challenging to clean.

Does anyone have recommendations for a safe product or a home remedy that could help us clean it out? I’m hesitant to just spray water in there, as it might make any existing obstructions more difficult to remove later.

I’m considering using an emulsifier. I’ve had success with a biodegradable engine cleaner that rinses off easily with a hose. The label doesn’t specify any concerns about using it around aluminum, and considering the high percentage of aluminum parts in today’s engines, I think it should be okay, but I’d appreciate any suggestions.

Additionally, I’ve noticed that the two pleated paper filters we provided, which are 20 by 20 and designed for a home furnace, were slightly damp when I checked them. Originally, there was a metal reusable filter similar to what fits above the evaporator for the driver’s A/C. Since the face of the evaporator is 20 by 40 and the adjacent bay is the plumbing bay in the motorhome, we can’t use a single-piece filter like what probably existed originally, as it wouldn’t fit in and out easily.

[MyPrevost]

Joe,

I recommend trying **Aviation Simple Green**. It’s specially formulated for use on aluminum and can typically be found online or at most general aviation airports. Given your concerns about damaging the aluminum parts of your system, this cleaner would be a safe option.

Other cleaners might work, but unless you can guarantee a thorough rinse, you could run into future issues. Aviation Simple Green is designed to be safe for aluminum, so it’s a solid choice for your needs.

[MyPrevost]

Thanks Jon

How about the filter on that evaporator? Is it a reusable washable metal, or disposable pleated paper?

[MyPrevost]

Maybe you just have the coach equivelent of a rat in the skimmer? I think the PlasticKrakster knows how to handle that kind of deal.

[MyPrevost]

Joe,

I have a three-part filter in the return air to the evaporator. It’s a fairly open weave, not a fine mesh, which allows me to easily wash it with a hose. You don’t need a filter that traps fine particles or microbes, but it’s important to catch dust and things like pet hair.

I clean mine annually, and it’s never overly dirty, so if you can install a filter in the return duct, a normal furnace filter or something similar should work fine. Keep in mind that using a pleated paper filter might restrict airflow too much.

[MyPrevost]

This filter isn’t located directly against the evaporator; it’s situated in the air return register on the floor, right?

Also, I found out about a product called Coil Bright available at appliance repair shops that’s specifically designed for this cleaning task. There are two versions: one for the evaporator and a stronger one for the condenser.

I plan to give it a try on Monday.

[MyPrevost]

Thank you, Jim; I appreciate your help, but I can take it out myself.

My question was aimed at Jon regarding the placement of the filter on his bus by Liberty.

[MyPrevost]

Joe: Jon is correct about filter density. Using a more restrictive filter can restrict airflow. Also, check the fan blades for any dirt buildup; forward-curved blades lose efficiency when they get dirty. You might also be dealing with a weak fan motor or switch that’s affecting airflow. If you opt for better filters, you’ll need a larger area to accommodate them, which you may not have space for. Please keep us updated on the results, as many of us face similar issues.

[MyPrevost]

Joe,

In my 1987 model, the filter was situated in the floor beneath the dinette seat. I’m not sure if that was a Liberty or a Prevost filter.

In my current coach, there’s a Prevost filter at the top of the evaporator bay. It consists of a rack with three filter sections positioned side by side. The opening from the house is beneath the cabinetry in the kitchen area.

Harry brings up a great point about the squirrel cage fan blades. When the curved parts accumulate dust, they lose their effectiveness as the curve becomes straighter, significantly impacting efficiency. He’s pretty sharp for an older guy, isn’t he?

[MyPrevost]

Thanks!

It appears that Prevost might have modified the configuration of the evaporator filter, relocating it from the front of the evaporator to the top of the compartment. I’m guessing this change was made to help prevent moisture accumulation on the filter.

I plan to move ours to the return air register to address that issue and also to simplify the filter replacement process.

[MyPrevost]

Wow, Harry!

That was actually some meaningful and relevant dialogue!

I’m genuinely impressed!

Are you Harry Hoppe, or is this another Harry?

[MyPrevost]

Jeep: Thanks for letting us hear from the other half of your brain.

[MyPrevost]

Joe, visit an air conditioning supply store and pick up a no-rinse evaporator cleaner. You can apply it using a pump-up sprayer, and as the name suggests, there’s no need to rinse it afterward.

[MyPrevost]

Welcome, Colton! Congrats on your first post!

I hope you enjoy your time here amidst the delightful mix of characters we have.

Is your nickname related to Colton, CA at all?

[MyPrevost]

Joe: Back in the day, you’d use carbon tetrachloride to rinse the coils, but now it’s off the market. They’ve packaged similar products as coil cleaners and charge a premium for them. Those old brass fire extinguishers used to be filled with the stuff!

[Author]

Posts