HVAC Buying and Troubleshooting Guide - Online RV Supply

HVAC Buying and Troubleshooting Guide


Understanding your RV's Heating, Ventilation, and Air Conditioning (HVAC) systems is an important part of keeping you comfortable. Learning more about how to troubleshoot and maintain these systems will help you avoid breakdowns, save money, and know what to buy when you need to replace them.

Initially the issues can seem complicated, but there are a few simple ways even a novice can troubleshoot these vital items. We will go over what you need to know about how things work, including a describing the main types of AC units, furnaces, and heaters. 

Almost all RVs available today incorporate a forced air system, and many have both heating and cooling in one unit.


The most common HVAC systems used today are rooftop units, designed specifically for RVs, that bring in outside air and either heat or cool it. They are available in a wide range of sizes and power levels to match different RV models. Bigger RVs may have more than one unit in order to control the environment throughout the vehicle. A main benefit of these rooftop systems is the limited interior footprint, but the trade-off is increased overall vehicle clearance.

If clearance is a concern for you, there are low profile options available to limit the impact. Low profile units are also more aerodynamic and weigh less than the full profile options. Less weight and drag means smaller units impact your fuel economy less.

Here is an example of a regular rooftop unit:




And here is a low profile option:


Under Bench

Some RVs have "under-bench" or built-in HVAC.  These units are generally concealed in a cabinet or other structure.  This trade off of loss of interior space is offset by ducted air flow, allowing the warm or cold air to be distributed throughout the interior cabin via air ducts. This can allow for a more even climate and comfort, just like a central heating and air system in a home.

Here is an example of an under bench with ducts, ready to be installed in a cabinet or under a seating or sleeping area:

Proper Sizing

To determine the proper size for your HVAC system, you will need to understand the rating systems for RV air conditioning units. They are usually referred to in terms of "British Thermal Units" per hour (BTU/hr), which represents the amount of energy that the unit adds or removes from the air.  Common sizes range from 10,000 BTU to upwards of 20,000 BTU/hr.  Since BTUs are a measure of thermal energy, the more powerful the A/C or Furnace, the higher the BTU/hr rating and the quicker your RV heats or cools.

Sizing your HVAC system is a matter of design and size of space, however most RVs have them preinstalled so you are just replacing existing units or upgrading power. Another consideration is the outdoor climate you will be operating in and the insulation levels of your particular RV.

RV Air Conditioning Parts and Components

While layout and positioning of the units vary, the underlying physics and basic mechanical and electrical parts are the same. Hot ambient air from inside your vehicle or home is pushed or pulled via fan over a set of metal coils that absorb that heat and transfer the energy to a special chemical that is inside the coils. These coils are known as evaporator coils.

That chemical (called a refrigerant) is heated past its boiling point and expand, thus carrying away the heat. Now in gas form, the refrigerant is moved away by a special pump called a compressor and is converted back into a liquid (at high pressure). This high temperature liquid is passed through another set of coils, called condenser coils, which allow the heat to dissipate into the outside air.

Keeping all this air moving is a set of vents and fans. It sounds a bit complicated but once you take a look its simple. The vents on a rooftop system are close together by necessity, but the intake and output vents in a ducted system are able to be spread apart.

Thermostats and Control

Controlling all this is your thermostat and On/Off switches. Thermostats are changing to digital but analog still exist. Depending on your set up, there may be individual zones where the temperatures can be set independently. 

Digital Thermostat


Much of the time, all you need is cooling, but if you venture into colder climates or travel in fall and winter, you might need supplemental heat. Many RVs come with heaters and insulation but not all are made to be used year round. Measured in BTUs as well, furnaces and heaters are made to really add some warmth.

In terms of how the heat is created, there are two general classes: Heat pumps and propane furnaces. While a propane heater uses the burning of gas to create heat, a heat pump is almost like an Air Conditioner ran in reverse. These elements even exist in the rooftop air units.

Since heat pumps rely on the outside air to provide heat, they are limited in effectiveness in temps below 45-50 degrees. Some heaters might have a small electrical element but the overall system will struggle to keep temps high enough in cold weather. In this case you will likely need a propane heat source. Depending on your plans, you might not need an entire system, you might be able to get by with a floor heater or small plug in unit.

RV AC Troubleshooting and Repair

Now that we know the basics, let's take a shot at fixing your problem before replacing the entire unit.

Often you don't need to replace a unit when a quick trouble shooting will do. Many issues do not require a call to your local repair experts, and you likely can achieve more than you think when it comes to AC repair and maintenance.

Start with your thermostat, the issue might lie in the ability of the thermostat to communicate with the AC unit. If you have a battery operated  thermostat, check that the battery is new and has a good connection. Remove any corrosion you might see in the battery box.  If you have a wired thermostat, double check its connections as well, making sure it is getting power.  For in depth wiring checks, consider getting a skilled repairman to take a look.

Next, check those AC filters. A clogged filter keeps the airflow from properly moving throughout the system and can limit the effectiveness of the cooling or heating. Its important to replace your filters often, to keep a good air flow rate and eliminate dust and other particles before you end up breathing them in. If it has been a while, give them a check.

Another issue that occurs is the AC refrigerant might have leaked out. The most common chemical is called Freon, and it can escape from tiny cracks or imperfections in the rubber seals or metal piping that contains it. Check your system closely to see if you have any signs of leaks, be it pin hole cracks or even tell tale chemical residues. If you think you might have an issue, try sealing these openings, then you can often get replacement refrigerant. If you suspect a bigger leak, have a pro come out to test the integrity of your system. They will bring a set of gauges and valves to check the pressures.

After you've cleaned the unit, checked filters, and looked for leaks, you might still be having problems. Take a look at the coils and make sure they are unobstructed and clean.Use a light brush and a vacuum to remove dust and debris.

Now it is best to start looking for failed interior parts. Normal wear and tear over the seasons takes it toll and all parts eventually wear out. Start with verifying you have fans that are unobstructed and spinning, that your compressor is working, and the system is free to move.

Check out our other tutorials or hop on over to YouTube. Many videos exist for units from most major manufacturers and you'll surely find something to help you get the job done!

RV Air Conditioner Buying Guidance


If you are reading this far, you probably are out of repair options and looking to replace. Or perhaps your RV didn't include enough factory installed AC or heat and you are looking to add some capacity. Here are some features to look for and some tips on what to avoid:


Rooftop air conditioners are installed over the window in your vehicle’s roof. The roof must be flat to allow for a good seal and there must be room for the exterior of the unit on your rooftop.

Here's what to keep in mind:

  • Rooftop ACs save valuable space inside your RV. For owners of smaller RVs this is very important and allows you to save space for things that matter!
  • Unless you buy a unit with a built in window, light will not be able to enter. If you'd like to keep the sky light functionality, look for a unit with an integrated skylight!
  • Since a rooftop unit is small, the cooling or heating air can only travel so far. This can create warm or cold spots, so look for a unit with good adjustable venting, or consider an air box add-on that distributes the air more evenly.
  • Since it's mounted on the roof, a rooftop unit will add to your vehicle’s height, however, a sleek, low-profile rooftop model will minimize this greatly.
  • Remember that heat rises, so while that's good for an AC to be mounted high, it's not great for heaters. Look for ducted options if you need more than usual heat.

An under bench air conditioner is located inside the vehicle – under a bench or in a compartment. It is ideal if your vehicle’s roof is curved or crowded with other devices.

Keep in mind:

  • Using a larger under bench will mean giving up space inside. This might not matter if your RV is large enough or your storage spaces are set up with this in mind.
  • Under bench units do not obstruct any windows and allows for a clean, out of sight, out of mind installation.
  • All under bench units use ducting, which means you are able to direct your air to the perfect spot throughout your living space. No more cold or hot zones!
  • Since they are mounted inside, these units do not add to your vehicles clearance, letting you travel to more places and with better peace of mind.
  • Since these units are mounted low and use ducts, they work best when it comes to providing heat, since it gets to where it needs to be. The heat is distributed far more effectively from under the vehicle which offers the added advantage of less energy consumption.


The “cooling capacity” of an air conditioner (sometimes referred to as pull down power) indicates the speed at which it cools air. This feature is measured in British Thermal Units per hour (BTU/h). If you want to feel a drop in temperature as quickly as possible, then choose an air conditioner with a high cooling capacity.


Some units include air purifying technology to remove odors and particles. This means you are breathing in more fresh air and less pollutants! Some units are all in one: combining Heating, Cooling, and Air Purifying in one.


Double check that your RV has the correct electrical connections to handle the added amperage draw of your HVAC changes. Fuses and breakers should be sized accordingly and remember to be safe when considering fire and electrical safety!

You might also consider a generator if you are looking to be "off grid" and still have access to all the power appliances you have grown to love, including that precious air comfort system!

Speaking of power usage, make sure to choose a unit with high efficiency to save power, money, and the environment. If you anticipate running your HVAC system while driving, look for options to run on 12 volts to use your vehicle battery!

In Conclusion

There is a lot of information to consider when making a choice for a new or replacement climate system. With this guide and our customer service, we can help you make a decision that keeps you on the road and comfortable for years to come!

Give us a shout if we can help with anything!
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