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How Do RV Air Conditioners Work? RV AC Repair, Maintenance & Troubleshooting


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Air Conditioning System 101

If you’ve ever wondered how air conditioners for RVs work, in a nutshell, it does so using a similar refrigeration process as used by kitchen fridges. Keep reading to get to grips with your AC system and avoid blowing hot air.

So, How Do RV Air Conditioners Work?

An RV’s air conditioning system draws in the surrounding warm air, uses a refrigerant to cool it down, and then expels it back out into the surrounding atmosphere. A process known as the refrigeration cycle.

The refrigeration cycle requires both evaporation and condensation. An obvious example of evaporation is when we boil water, but boiling our coolant would only add heat to our system, and we don’t want that!

Instead of causing evaporation and condensation by adjusting the temperature, we change the pressure. If we remove pressure from a liquid coolant, it evaporates and absorbs heat. Then, if we add pressure to that evaporated vapor, it condenses and releases heat. 

This is the secret to how RV air conditioners work. A compressor pressurizes the refrigerant vapors into a hot liquid. This liquid flows through the condenser, and fans blow cooler air over the condenser to release heat into the atmosphere. 

Once the liquid is cooled down, it flows through an expansion valve into the evaporator. In this step, the cool liquid evaporates into a gas and expands. This cold gas flows through coils, and fans blow the heated airflow across those coils. This cools the surrounding atmosphere and in turn, creates a comfortable temperature inside your recreational vehicle.

Unlike AC in the home, air conditioning for trailers and RVs is in a closed system and so there are no concerns over potential leaking coolant.

In RVs, AC is usually in a roof-mounted unit so as to preserve already limited floor space. Usually, vehicles are fitted with an RV roof mount air conditioner as standard and vary in quality between brands. 

If you are looking to upgrade your current rooftop RV AC, or haven’t yet had one installed then check out our handy guide to the top roof-mounted air conditioners for RV living.

Explanation of the Parts

There are four main components to an AC unit:

  • Compressor
  • Condenser coils
  • Expansion valve
  • Evaporator coils


The compressor is the workhorse of the entire system, pressurizing the refrigerant coolant from around 30 psi to as high as 240 psi! This forces the coolant into a hot pressurized gas state that flows through the condensing coils.

As this heated gas flows through the condenser coils the heat dissipates into the surrounding atmosphere, typically helped by a fan, and the heated gas cools down. These coils can become pretty warm, usually around 125 degrees Fahrenheit. As a consequence of the gas losing its heat, it turns back to a liquid. 

Typically for a stationary AC unit for a house, the condenser coils would be located outside the building so that they don’t reheat inside. In an RV air conditioning unit, there will be an exhaust hose fitted so that this heat is vented to outside the RV.

Once the liquid-state fluid is cooled down to ambient temperature, it is regulated through the expansion valve. This valve controls how much refrigerant liquid flows through to the evaporator coils inside the vehicle and this controls how an RV air conditioner works.

The refrigerant fluids then flow through the evaporator coils which are under less pressure and this causes expansion into a gas state. This process absorbs heat from the atmosphere inside the vehicle due to evaporation, and this lowers the internal temperature to a more comfortable state.

A fifth component, which is often overlooked but necessary, is the fan system. Both the condensing coils and the evaporator coils need to have an airflow blown across them to facilitate the cooling power and usually, this is accomplished by fans on both sides.

Air Conditioners Demand Lots of Energy

RV air conditioning works by consuming a lot of energy. It’s not uncommon for your AC to use more energy than any of your other appliances

Evidently, you will need enough power to run your RV’s AC unit from an external AC power source. This is typically from campsite shore power, a generator or increasingly popular is to also have solar panels to use solar power, in combination with a backup generator, to produce enough energy to power your AC unit.

Fortunately, there are ways you can try to conserve energy when using your RV’s air conditioner as well.

RV Air Conditioner Efficiency Tips

Efficient running of your AC will not only save energy but also helps RV air conditioners do their job by lowering the internal temperature to a comfortable level. Follow these tips to find out how to keep your AC system running at its best.

Routinely Check and Clean Your AC Filters

Just like AC in your home, you need to clean or replace your RV’s AC filters regularly. When the filters become dirty, the AC unit needs to work harder to force airflow past the coils. This is work that could be better used for the refrigeration cycle itself.

A dirty filter will also slow down the air conditioner’s airflow into the cabin, so eventually, you might not feel the airflow at all. 


The worst thing that can happen with dirty filters is that they can become contaminated with mold or bacteria. When the cabin airflow goes through these filters, sometimes the toxins can be released, and you might risk getting yourself or your family members sick.

So, for health reasons, and also to ensure your RV AC unit runs efficiently, keep your filters clean. Your RV air conditioning filters can usually be sprayed with a hose and then dried naturally, or blown out with an air compressor.

Use Fans, With or Without Your AC

Sometimes, your RV central air conditioner might be working fine, but you aren’t feeling the cooling effect because of insufficient cool airflow circulation. Appliances and furniture inside your RV can obstruct airflow so that cool air never reaches your seat or your bed.

If a thermostat controls your AC, this control might be malfunctioning due to pockets of colder air near the thermometer. The thermostat works best when the cabin air is at a consistent temperature at every point, and the best way to achieve this is with interior ceiling fans.

Furthermore, fans (and proper cool airflow circulation) can make a person feel up to 10 degrees Fahrenheit cooler by removing layers of stagnant air that settles around the human body and prevents convection. 

A fan uses much less current than your camper roof air conditioner, so for all of these reasons, it is much more efficient and practical to use fans in conjunction with your AC to keep your RV cool.

Always Park in the Shade If Possible

Wherever your RV travel destinations end up being then, for obvious reasons, your RV camping experience will be much cooler and comfortable if you can park in the shade.


Since the AC coils need to purge heat from the coolant outside the vehicle, it is much easier for them to so in the shade than it would be in direct sunlight. If the outside coils get too hot, trailer air conditioning units may not work at all.

Close off Parts of your Vehicle That You’re Not Occupying

You might be lucky enough to have a large, spacious rig. However, this spaciousness can work against you.

AC units are rated by how many tons of cool air they can generate, so a larger RV will be harder to cool than an RV with more limited space.

You can help keep fresh inside your RV by limiting the space that your AC is cooling. Do this by closing doors to bedrooms and bathrooms while they’re not being used. The temperature inside those closed-off spaces might rise, but the room in which you’re sitting will stay cool and enjoy the full power of your roof-mounted RV air conditioner.

Avoid Using Appliances That Add Extra Heat Into the Atmosphere

You will feel much more comfortable and cool inside your RV if you make sure not to run other heat-generating appliances when you’re using rooftop RV air conditioners.

Cooking, showering, and running laundry can all contribute to your RV heating up. When this happens, the AC must work harder to remove this excess heat.


Aside from contributing extra heat, these appliances also draw additional electric current that the AC unit might need to work correctly. After all, how can an RV air conditioning system work properly without adequate electrical current?

Thoroughly Insulate Your RV

Maybe your AC is working fine, but you’re asking, “How can my RV air conditioner work better?” A well insulated RV will keep you more comfortable not only when using your AC in the summer, but also when camping during the cold winter months.

Lining the walls with fiberglass or rigid foam insulation will prevent the summer sun from turning your RV into a portable oven. It will also prevent heat from escaping your RV during chilly winter nights.

Fiberglass and rigid foam are trying for a novice RV owner to install, but spray foam insulation can be a cheap and easy-to-apply solution.


When insulating your RV, don’t forget your windows. Windows can be a significant source of heat loss or heat intrusion, so it might be worth the cost to upgrade to multiple-pane insulating windows. Of course, having your windows closed as much as is possible will also help.

Maintaining Your RV AC Unit

Performing regular maintenance on your AC unit should be part of your regular RV maintenance routine and should ensure you never have to get an AC mechanic involved. Along with checking your RV AC manual the following steps are simple measures that you can take to keep your AC functioning properly.

How to Clean the Filter

The AC filter is usually just behind the interior vents. Open up the air vent and carefully remove the filter so that you don’t shake dust and contaminants into the cooling coils.

If the filter is made of woven plastic mats, it can be cleaned easily with a hose or air blower. Take the filter outside and spray or blow the dirt free. Ensure that you thoroughly dry the filter before replacing it on your RV AC roof unit.

Video: https://www.youtube.com/watch?v=on67V50lHOE

If the filter is made from fiberglass with a cardboard frame, this is meant to be disposable. Check your auto parts store or hardware store for replacement filters.

Locating and Accessing the Condenser and Evaporator Coils

Even with regular maintenance of your AC filter, your coils may occasionally become dirty.

You can access your evaporator coils by removing the filter on the interior part of your roof top RV AC unit. You will find the evaporator coils right behind that filter.


The condensing coils are usually located under a casing on your AC unit’s exterior. If you remove that protective cover, you’ll find the condensing coils underneath.

Cleaning the Air Conditioner Coils

  1. Turn off the AC system and disconnect the current at the breaker box.
  2. Remove the casing (from the exterior unit) or the filters (from the interior unit) to expose the coils.
  3. Inspect the coils for any visible damage or large debris. Interior coils, if they have been substantially clogged, can form ice build-up. If this happens, place a pan or a bucket underneath the coils and wait for the ice to thaw.
  4. Brush the coils with a soft-bristled brush to remove dirt and small debris. Frequently wash the brush in warm water to rinse off dust and oils.
  5. Straighten the coils with a fin comb. This is a special fine-toothed comb that will straighten and restore the coils to their original shape and function. Brush the coils in one constant motion from top to bottom.
  6. Rinse the coils with a mild soap solution. You can use a spray bottle and a mixture of dish detergent and warm water.
  7. Allow the soap solution to soak into the coils for 5–10 minutes to dislodge stubborn grease or oils.
  8. Rinse the soap solution off with clean water. Keep the pan or bucket underneath the coils to collect the runoff.
  9. Allow the coils to dry before replacing the filters or casing.

Maintaining the Fan Motor

The AC fan motor is a vital component to keep the system running smoothly. Cleaning and maintaining this motor is a similar task to cleaning and maintaining the coils.

  1. Make sure the AC system is shut down and disconnected from the current at the breaker box.
  2. Locate the AC fan and remove the outer casing to expose the blades and motor.
  3. Clean the fan blades with a wet rag.
  4. Clean the motor shaft and remove any debris that might be entangling it.
  5. Tighten any screws that house the blade set to the motor shaft with a long-tipped screwdriver.
  6. Using a non-detergent motor oil, apply a few drops in any oil ports or motor shaft housings.
  7. If the fan has been malfunctioning, check the motor with a multimeter to ensure that the electrical resistance is between 3 and 30 ohms. Connect the leads on the VOM multimeter to the terminal wires on the fan motor. Low or high resistance means the motor should be replaced or repaired.

Covering Your RV AC Unit When Not in Use

When your RV is not in use, you should cover the external AC unit with a plastic tarp to prevent dirt, debris, and precipitation from clogging or damaging the unit. Rainwater or snow can slowly cause rust in the coils that are difficult to remove.


Once the RV air conditioner cover is in place use bungee cords to hold it on tightly. If your vehicle is outside make sure the tarp is secured enough against high winds and stormy weather conditions.

Always remove the tarp before traveling as operating the AC unit while covered can overburden the motor or even cause the tarp to catch fire.

RV Air Conditioner Repair & Troubleshooting Steps

If you’re still having trouble with your RV AC system, try the steps in this troubleshooting checklist.

Step 1: Check the Power Source

Travel trailer air conditioner units might draw as much as 16–20 amps of electric current. If you want to use your AC, you need to be plugged into shore power at a campground pedestal or a large generator.


The power source connection might only be providing 30 amps of current. So if you’re using any other appliances simultaneously while running your AC, this might be causing problems.

Some indications you are having power deficiency issues are:

  • The AC unit won’t turn on
  • The compressor is not coming on
  • The RV air conditioner is not blowing cold

You can check the power with an electric multimeter, or by asking the campground manager to check the power station.

Step 2: Find and Test the Capacitors

There are two capacitors in most RV air conditioners. These capacitors store energy to start and run the motor and are essential for travel trailer AC units to run efficiently. The indications that one of these capacitors are malfunctioning is:

  • The AC fan is not working
  • The compressor does not come on.

To troubleshoot the capacitors, you can follow these steps:

  1. Shut off the AC power at the circuit breaker.
  2. Locate the capacitors. They are usually in a compartment on the exterior AC unit.
  3. Discharge the capacitors by shorting the terminals with a flat blade screwdriver.
  4. Remove the electrical leads from the capacitor and then remove the capacitor.
  5. Test the capacitor with a multimeter set to “capacitance mode.”
  6. Compare the multimeter reading with the value printed on the side of the capacitor. 

If the capacitor is bulging in any place, that means it has overheated and should be replaced, regardless of any measured readings.


Step 3: Test the Switches and Thermostat With a Multimeter

Your thermostat might be broken which can easily be checked with the “voltage” setting on your multimeter. 

If the thermostat or AC switches are not working, this is what is stopping the AC unit from working efficiently. You can order replacement parts from your auto parts store. Note the serial number on the side of the thermostat before ordering.

Step 4: Check If the Fans Are Working

If you can hear the compressor working but can’t feel any cold air coming from your AC, this means the fan is malfunctioning. Remove the vent cover and filters to check the fan behind the coils.

This problem may be solved by cleaning and lubricating the fan motor, or it might require replacing the capacitor (as mentioned above).

If these solutions do not work, you may have to replace the fan motor. This is a task best suited to a professional mechanic.

Step 5: Listen for the Compressor Functionality

You can usually hear when the compressor kicks in. It has a deeper, rumbling sound that’s unmistakable. 

If the compressor is not working, it’s probably not efficient or cost-effective to repair it. The compressor is the hardest-working part of the AC system, and when it breaks, you might need to replace the compressor or even your entire AC. The compressor is the critical component in how AC units work.


Now that you have a better understanding of how an RV AC unit works, you can travel in cool comfort with confidence. Make sure to follow all of those tips for keeping your RV cold and maintaining your AC unit.

If you found this article informative and helpful, please share it with other RV owners, especially friends and family members, who might need to know how RV AC systems work. Let’s all make sure everyone keeps cool on those hot summer vacation days!

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