Tech- Tune up your rooftop A/C

May 8, 2008

In some parts of the country, the heat is already here- in other parts, it’s well on its way, so I thought it might be good to talk about giving your rooftop air conditioner a basic tuneup.

A couple of things to remember about roof top RV air conditioners- all air conditioners work by removing heat (actually, all refrigeration works that way- as do heat pumps), and RV air conditioner- as they come from the factory- are hermetically sealed, and they only hold about 1 pound of refrigerant (at this time, R-22 is the refrigerant used). The point of this is that with less than 1 pound of refrigerant and a sealed system, 99% of the time, “not enough cooling” complaints are due to air flow issues, and not lack of “Freon®”

Luckily, the average fix for this is easy- clean the coils! Let’s take a look at how to do this….

These procedures do involve some risk- you will be working on the roof of your RV, and working around 120 volt systems and devices which can store power even when shut off.
Always observe all common safety procedures!!

Unplug the rig, disconnect the battery, don’t fall off the roof…. you get the idea!

A word about RV roofs- most modern RV roofs are plenty able to support a person walking on them, but use your own judgment- if the roof seems springy, lay a piece of plywood to walk on, and if the roof is an EPDM roof, take care to not damage the membrane- make certain your feet are clean, and pick up your feet before turning them (which causes bubbles)

There are some basic and some advanced maintenance items that can be performed on roof top air conditioners- I will mention some of the advanced items, but illustrate the basic ones.

To get an idea of what we are dealing with, I’ve drawn a “typical” cross section of a roof top air conditioner:

The first basic area is the air filter. In summer, using the RV and air conditioner around the clock, the filter should be checked weekly and cleaned as needed. RV air conditioners use either a foam type filter or a fine mesh, both of which can be rinsed in water and reused. I cannot stress this enough- keep the filter(s) clean!

After a few years, even the best filter will let enough dirt past to coat the evaporator coils, though, so they need to be cleaned. If the coils are not too dirty, and if the installation leaves enough room to access the coils, you can simply buy a can of spray coil cleaner and use that- saturating the coils, letting it sit for a bit, then running the air conditioner so that the condensation will rinse the coils off.

A tip though- be very careful in choosing a product to use- a lot of commercial coil cleaners such as would be found in home center type stores can be pretty strong- not something I would like to run over the outside of my RV, so I only use Enviro-Chem coil cleaner, specifically made for RV use.

But- sometimes the coils are just too dirty to simply be rinsed off like this, or access from the inside is restricted enough that a trip to the roof is needed.

The 2 most common models are the DuoTherm Brisk Air and the Coleman Mach series , though the cleaning methods will be the same for every brand and model.

The first task is to remove the shroud- either screws around the base of the plastic (DuoTherm and Carrier), or screws in the top (Coleman).

Once you have the shroud off, you have to get to the evaporator, which is at the front of the unit under a (usually) sheet metal (sometimes styrofoam) cover.

The evaporator cover (if it’s metal) will be attached by a number of sheet metal screws, remove these, but pay attention to the screws as you remove them. On some models there will be either different length screws, some screws might be blunt ended to go in to electrical areas. Just pay attention and replace the screws in the same way they were removed.

Once the cover is off, you can see the evaporator coil. Note in this picture, the “freeze” control is not installed in the proper place (only ducted installations use a freeze control).

Now it’s simply a matter of cleaning the coils. Coleman recommends “Formula 409”, I use VoomRV, which is a ph neutral degreaser.

Soak the coils well- if there is a lot of crud on them, I use a bristle brush to clean the coils- carefully, as the fins are delicate, to scrape off the crud. Another option is using a “fin comb”, which is also good if the fins are bent, restricting the air flow.

While these coils are soaking, do the same thing for the condenser coils- soak them well with the cleaner. I can usually measure a 1 to 2 amp decrease in current draw simply by cleaning the condenser coils- this on 1 to 2 year old air conditioners.

Next comes the tricky part- rinsing the evaporator coils without flooding the rig. It’s not hard- put down towels in the air return opening, and don’t use too much water pressure- the cleaner will do the work, you just have to rinse the coils off. Do this on both evaporator and condenser coils.

A couple of advanced items- when I do this service, I also will check the gasket to make sure it’s still in good shape, I will check the current draw on the unit, and I visually check the electrical connections to the A/C electrical component – the start and run capacitors, etc.

And…. that’s it! Button everything back up, and know that your air conditioner will be able to take as much heat as possible out of the inside through the evaporator, and get rid of the heat through the condenser.