There are some tips and tricks to making your roof AC run more efficiently and provide a cooler interior climate.

Become Familiar With Your Roof AC

The first thing to do is become familiar with how the roof AC operates and what you can expect.  Most RVers think the roof AC uses a coolant such as Freon to “dump” cold air into the rig but this is not the case.  The roof AC operates very similar to your absorption refrigerator and actually draws heat from interior air through the evaporator at the front of the unit.  Warm and humid interior air is drawn up to the roof AC through the return air vent, passes over the evaporator coil and heat and moisture is extracted from it.

If you were to take the cover off the roof AC unit and the evaporator shield you would see the evaporator fins getting very wet immediately and the moisture forming at the bottom on the drip pan.  The compressor does just that – compresses the coolant and pushes or pulls it through tubes known as the low side and high side which changes it from a liquid to a vapor.  This in turn draws moisture and heat in the evaporator and the air is then circulated back into the rig just behind the evaporator coil by the blower fan.

The coolant passes through the back condenser fins where the blower motor draws exterior air in and over the coils with the Freon.

With an understanding of how the system works, it’s important for owners to do a little bit of maintenance so there is proper air flow, sufficient amperage, and no air leaks in the system.

Proper Air Flow

The return air coming from the inside to the evaporator will have a filter. Roof-mounted units with the conditioned air coming directly out of the bottom will have the filter designed into the ceiling shroud.

Units with ducted air vents in the ceiling will have a grill on the ceiling.

These filters should be cleaned at least once a year and typically more depending on usage and how much dust might be in the air.  Most dealers indicate a dirty filter is over 50% of the issues with a roof AC cooling inefficiency!

Next, make sure the vents are open and operating properly on a ducted roof AC system.  Closed vents will restrict air flow, causing high amp draw and condensation.

• Check and clean the condensor and evaporator coil every year.
• Dust, pet hair, and even body powders can get pulled into the return air and clog the coils.
• There are specific cleaners for the evaporator and condensor coils that should be used each year.
• Since the evaporator coil is in the front and goes directly to the opening for cool air to the rig, you will need to do a low pressure clean and have a plastic sheet over the blower fan return to keep moisture from entering the rig.
• Do not use high pressure water as it will not only make a mess, but will damage the coils.
• Once the coils are clean, make sure they are straight and will allow good air flow.  There are even brushes or combs available to help straighten the fins on the coils.
• Typically the evaporator coils do not get damaged, rather clogged, however the condenser coils are exposed to the outside and can get hail damage or even tree branches.

Proper Amperage

The roof AC and several other appliances run on 120-volt power which is supplied from the shoreline connection or a generator to the distribution center.  Most RV owners take it for granted that the campground connection is a 30 amp 120-volt power system and they will have no problems just like they did at home.  Unfortunately, the campground source is not as reliable as a residential system and can have severe power loss situations.  If the power drops below 110-volts, the roof AC unit will not be able to function at 100% capacity and even though you hear the fans running and other components, it will not be able to draw the heat out and efficiently cool the unit.   This is why a Surge Guard protection unit is a good idea as it will monitor the incoming voltage.

Air Leaks

Your roof AC unit is mounted with a gasket between the unit an the roof typically with 4 spring loaded fasteners that should be checked for specific torque or tightness every year.  You should be able to find the torque specs in the roof AC owner’s manual however a good hand tightening should be good.  If the gasket is not tight, you will get hot moist outside air coming into the unit and rig which will make it difficult to condidtion the exiting air.  Also, check to make sure you are not getting hot and moist outside air from vents, windows, and event roof ducting.  Seal all the leaks during hot and humid conditions and your roof AC will work more efficiently.

The roof AC can only cool the return air from the inside down about 20 degrees, so if the inside of your rig is 100 degrees, you will only get 80 degrees air back inside!  So the key is to try and keep the inside air temperature as low as possible so the roof AC can run more efficiently.

About the author:

Dave Solberg: Managing Editor, RV Repair Club

For the last 25 years, Dave has conducted RV maintenance and safety seminars, developed dealer and owner training programs, written RV safety and handyman articles, authored an RV handbook reference guide and logged over 100,000 miles on the road in an RV.

RV Repair Club is your go-to online resource for enthusiasts who want quality RV maintenance, repair, and upgrade information – a community where passionate RVers can come together to gather knowledge and share their experiences.

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