When you decide to tackle an RV air conditioner installation, success boils down to three key stages: meticulous prep work, safe and steady handling during removal and placement, and a secure electrical hookup. This isn’t just about bolting on a new appliance; it’s about having the right gear, confirming your RV’s roof and wiring are up to the task, and carefully following each step to ensure a leak-proof, efficient new AC for your travels.
Your Pre-Installation Game Plan and Checklist
Before you even think about climbing that ladder, remember that a good installation starts with a solid game plan on the ground. Diving into this project unprepared is a recipe for multiple trips to the hardware store and risks damaging your rig. Think of this as your pre-flight check to guarantee installation day goes smoothly, without any costly surprises.
With RVing more popular than ever, DIY projects like this are becoming common. The global market for RV air conditioners hit about USD 1.35 billion in 2024, which shows just how many of us are out on the road. And with around 0.7 million RVs sold each year in North America, knowing how to prep for a new AC install is a skill worth having.
Confirming Compatibility and Readiness
First, you need to make sure your RV is actually ready for the new unit. This goes beyond just having a 14×14 inch hole in the roof—we’re talking about structural and electrical integrity.
- Roof Support: Can the roof around your vent handle a new AC unit, which typically weighs between 70-100 pounds? Most RVs have reinforced framing around the standard 14×14 inch vent opening, but you must check for any soft spots or signs of water damage that could signal structural weakness. Gently press around the opening; it should feel firm and solid.
- Electrical Capacity: A new air conditioner pulls significant power. You have to confirm that your RV’s electrical system and the circuit breaker it’s on can handle the amperage draw of your new model. A 15,000 BTU unit, for example, absolutely needs its own dedicated 20-amp circuit.
- Power Source: Consider how you’ll power the AC. Will you be on shore power, or do you need your generator to run it? Cross-reference the wattage needs of the new unit with your generator’s output. A 13,500 BTU AC generally needs at least a 3,000-watt generator just to start up and run properly.
Pro Tip: Never assume the old wiring is good enough. If you’re upgrading from a simple fan vent to a full-blown air conditioner, you will need to run a new, heavier-gauge 120V AC wire (typically 12/2 Romex) from your breaker panel all the way to the roof opening.
Gathering Your Tools and Materials
Having everything you need within arm’s reach is a massive time-saver and prevents you from constantly climbing up and down the ladder. This is your mission-critical checklist.
Before you start, it’s a good idea to lay everything out on a tarp or blanket next to your RV. This not only keeps you organized but also prevents you from losing small screws or parts in the grass.
Essential Tools and Materials for RV AC Installation
| Category | Item | Pro Tip |
|---|---|---|
| Hand Tools | Socket Set & Screwdrivers | A ratchet set with various socket sizes will make removing the old unit’s bolts much easier. |
| Plastic Putty Knife or Scraper | Essential for carefully removing old sealant without scratching or tearing the roof membrane. Avoid metal. | |
| Sealing | New AC Gasket | Never reuse the old gasket. A new one is absolutely critical for a watertight seal. We carry the Dicor Seal-Tite replacement gasket for 14″ x 14″ openings. |
| Dicor Self-Leveling Lap Sealant | The industry standard for a reason. Make sure it’s self-leveling for horizontal roof surfaces. Available in white or tan. | |
| Butyl Tape | Use this around the opening before placing the new unit for an extra layer of waterproofing. | |
| Safety Gear | Work Gloves & Safety Glasses | Non-negotiable. Protect your hands from sharp edges and your eyes from flying debris and sealant. |
| Sturdy Ladder | Make sure it’s on level ground and stable before every climb. Consider our aluminum platform step ladder for added stability. | |
| Lifting Help | A Friend (or two!) | Seriously, don’t try to lift the old unit off or the new unit on by yourself. They’re heavy and awkward. |
| Optional Tools | Caulk Gun | A ratcheting caulk gun makes applying sealant much easier and more consistent. |
Once you’ve got all your tools and supplies checked off, you’re truly ready to get started. An organized toolkit is the foundation of a job well done.
Time to Tackle the Old Unit or Roof Vent
Alright, with the prep work behind you, it’s time to get your hands dirty. Whether you’re removing a tired, old AC unit or just upgrading a standard roof vent, the key here is a methodical approach and a lot of patience.
Before you touch a single screw, your first job is to kill all the power. And I mean all of it. This isn’t a suggestion—it’s the most critical safety step. Unplug from shore power, turn off the generator, and shut down your 12-volt DC system using the battery disconnect switch or by physically removing the negative battery cable. Working on wiring when you think the power is off is a dangerous gamble.
Taking Apart the Interior Assembly
First, head inside the RV. You’ll need to remove the interior ceiling assembly, also known as the air distribution box. It’s usually just held on by a few screws. Once it’s off, you’ll expose the four main mounting bolts and the electrical wiring.
Before you unplug anything, grab your phone. Take several clear pictures of the wiring from different angles. This simple step can save you from a massive headache when hooking up the new unit. Once you’ve got your photos, you can carefully disconnect the 120V AC wiring. You’ll typically see a black (hot), white (neutral), and a green or bare copper wire (ground).
A friend of mine once skipped taking photos, thinking he’d remember the wiring. He spent an extra hour troubleshooting a dead unit, only to realize he had mixed up two connections. His advice? “Label everything, photograph everything. No exceptions.”
Moving the Job to the Rooftop
Now it’s time to head up top. Carefully climb your ladder and position yourself near the unit. You’ll see the old sealant creating a thick bead around the entire perimeter of the unit. This is what’s been keeping water out, but it also means the AC is essentially glued to the roof.
Using your plastic putty knife, gently work your way around the entire perimeter, breaking the seal between the old sealant and the roof membrane. Take your time—rushing here can tear the rubber roof membrane, which is an expensive mistake. The goal is to separate the unit from the roof without damaging anything.
Once you’ve broken the seal all the way around, you’ll need to remove the mounting bolts. These are typically four large bolts that go through the roof and are secured with nuts from the inside. Have your helper inside the RV hold the nuts with a wrench while you unbolt from the top, or vice versa.
With the bolts removed and the seal broken, the old unit should lift straight up. This is where having a helper is absolutely essential. These units are awkward and heavy. Lift slowly and evenly, making sure no wires or parts are still attached. Set it aside safely.
Cleaning and Prepping the Opening
With the old unit out of the way, you’re now looking at the opening. It’s likely covered in old, crusty sealant, dirt, and maybe some water stains. This needs to be as clean as possible before the new unit goes in.
Use your plastic scraper to remove as much of the old sealant as you can. Then, wipe down the entire area with a clean rag and some rubbing alcohol or mineral spirits. You want a clean, dry surface for the new gasket and sealant to bond to.
Inspect the opening carefully. Look for any signs of wood rot in the roof structure, any cracks in the roof membrane, or soft spots that might indicate water damage. If you find any problems, they need to be addressed before you install the new AC. A new air conditioner on a compromised roof is just asking for trouble down the road.
Installing Your New RV Air Conditioner
You’ve done all the hard work of removing the old unit and prepping the opening. Now comes the exciting part—installing your brand new RV air conditioner. Whether you’re upgrading to a more efficient model or replacing a failed unit, the installation process is straightforward if you follow these steps carefully.
If you’re shopping for a new unit, we carry a full selection of Coleman Mach air conditioners, including both 15,000 BTU models and units with built-in condenser pumps for better performance.
Preparing the New Unit and Gasket
Before you haul the new unit up to the roof, there’s some prep work to do on the ground. First, unpack the new air conditioner and inspect it carefully. Make sure there’s no shipping damage and that all the mounting hardware and instructions are included.
Most new AC units come with a foam gasket already attached to the bottom flange. This gasket is critical—it’s what creates the watertight seal between the unit and your roof. If the gasket isn’t pre-installed, you’ll need to apply it yourself according to the manufacturer’s instructions. Additionally, apply a bead of butyl tape around the roof opening for extra waterproofing before setting the unit in place.
Now is also a good time to familiarize yourself with the electrical connections on the new unit. Refer back to those photos you took of the old wiring. The new unit should have the same basic setup: a black (hot) wire, white (neutral) wire, and green or bare (ground) wire.
Lifting and Positioning the New AC
With your helper, carefully lift the new unit up to the roof. This is a two-person job, no exceptions. One person should be on the roof guiding the unit into place, while the other person is on the ladder helping to lift and stabilize.
Once you’ve got it up there, carefully position the unit over the opening. You want to make sure it’s centered and that the mounting bolt holes line up with the holes in the roof. Don’t force it—if it’s not lining up, there’s a reason. Check that the opening is clear of debris and that the gasket is seated properly.
When the unit is properly positioned, lower it gently into place. The foam gasket should compress slightly, creating a seal between the unit and the roof. Don’t worry if it feels a little spongy at first—that’s exactly what you want.
Securing the Unit and Making Electrical Connections
Once the unit is in place, it’s time to secure it. From inside the RV, start threading the four main mounting bolts through the holes. Have your helper on the roof hold the unit steady while you work from below.
Here’s the critical part: tighten the bolts in a crisscross pattern, not going around in a circle. Start with one bolt, give it a few turns, then move to the bolt diagonally opposite. Then go to one of the remaining bolts, and finally the last one. Go around a few times, gradually tightening each bolt evenly. This ensures the gasket compresses uniformly and creates an even seal all the way around.
Don’t overtighten. You want the gasket to compress, but if you crank down too hard, you can actually crush the gasket or crack the unit’s mounting flange. Tighten until the unit feels snug and the gasket is fully compressed, then stop.
Now, it’s time to reconnect the electrical wiring. Refer back to your photos. Connect black to black (hot), white to white (neutral), and green or bare to green or bare (ground). Make sure all connections are tight and secure. If the new unit came with wire nuts, use fresh ones—don’t reuse the old ones.
Once the wiring is complete, tuck it neatly out of the way and reinstall the interior ceiling assembly. Make sure all the screws are in place and the assembly is secure. You may also want to install fresh air filters at this point for optimal performance.
Sealing Everything Up
Back on the roof, it’s time for the final—and arguably most important—step: sealing everything with lap sealant.
Grab your caulk gun and lay down a generous, continuous bead of Dicor self-leveling lap sealant around the entire perimeter of the AC unit’s base. You want the sealant to cover the edge of the unit and spread out onto the roof membrane, creating a solid barrier.
More importantly, make sure you completely cover the heads of any mounting hardware or screws left exposed on the rooftop. Water loves to find its way through screw threads, and a thick dab of lap sealant is the only way to stop it.
A common mistake is being too stingy with the sealant. This isn’t the time for a thin, pretty bead. You want a substantial layer that fully encapsulates the unit’s seam and all the hardware. A leak-free roof is far more beautiful than a perfect caulk line.
Once applied, give the sealant plenty of time to cure according to the manufacturer’s instructions. This can take anywhere from a few hours to a full day, depending on the temperature and humidity. Don’t rush this part.
The Moment of Truth: Testing Your System
After the sealant has fully cured, it’s finally time for the moment of truth. Head back inside your RV, restore all power by plugging into shore power or firing up your generator, and flip the appropriate circuit breaker back to the “On” position.
Now, run your new air conditioner through all its functions. This isn’t just about seeing if it gets cold; it’s about listening and feeling for proper operation. Follow this sequence:
- Fan Only: Start by turning the unit to the “Fan Only” setting. Cycle through low, medium, and high speeds. Listen for smooth fan operation without any rattling or scraping.
- Low Cool: Next, switch it over to the low cool setting. You should hear the distinct “thump” or “clunk” of the compressor kicking on within a few seconds. The air from the vents should start to feel noticeably cooler within a minute or two.
- High Cool: Finally, crank it to high cool. The fan speed will increase, and you should feel a powerful blast of cold air. Let it run like this for at least 15-20 minutes to make sure it’s cycling correctly and actually lowering the temperature inside your rig.
While it’s running, pay close attention to any unusual vibrations. A properly installed unit should run smoothly without shaking the whole RV. If you run into any trouble, don’t panic. If you want to reduce power surges during startup, consider adding a soft start kit to protect your AC and prevent breaker trips.
Post-Installation Troubleshooting Guide
Encountering a hiccup after installation is frustrating but often a simple fix. This table will help you quickly diagnose what might be wrong.
| Symptom | Potential Cause | Solution |
|---|---|---|
| AC won’t turn on at all | No power to the unit. | Check that the RV is connected to power, the generator is on, and the AC circuit breaker is in the “On” position. Re-verify your wiring connections. |
| Unit runs, but no cold air | Compressor isn’t engaging. | Listen for the “clunk” of the compressor. If you don’t hear it, power down and re-check your wiring connections, especially the compressor wires. |
| Loud rattling or vibration | Mounting bolts are loose or debris is present. | Power down the unit. Re-check the four main mounting bolts and tighten them to the manufacturer’s specified torque. Check for debris in the fan housing. |
| Water leaking inside the RV | Gasket isn’t fully compressed. | The mounting bolts may need to be tightened further in the crisscross pattern to create a proper seal. Do not overtighten. |
| Fan sounds like it’s hitting something | Debris in the fan housing. | Disconnect power. Remove the interior and exterior shrouds to inspect the fan blades for any obstructions or leftover shipping materials. |
If you’ve run through these checks and still have issues, it might be time to consult the unit’s manual or the manufacturer’s support line. In most cases, however, a quick check of your work will get that new AC humming along perfectly.
Frequently Asked Questions
Even after a step-by-step guide, questions pop up. Every RV is built a little differently, so let’s dig into some of the most common questions from folks tackling this job.
Getting these details right matters. Roughly 25% of all complaints about RV air conditioners, like poor cooling or early failure, can be traced back to a bad installation.
Can I Add a Second Air Conditioner to My RV?
Yes, but you need to do your homework first. Many larger RVs are “pre-wired” for a second unit, typically in the master bedroom. You’ll see a standard 14×14 vent that’s already framed for an AC, with a dedicated 120V wire ready to go. If that’s your setup, the job is nearly identical to a simple replacement.
If your rig isn’t pre-wired, the project is more involved:
- Check for Roof Support: You can’t just cut a hole anywhere. You need to find a spot between the roof joists that can handle the 80-100 pound weight of an AC unit.
- Run New Wiring: This is non-negotiable. You must run a new, dedicated 12/2 Romex wire from your breaker panel to the new opening.
- Confirm Your Power Service: A second AC unit is only feasible if you have a 50-amp service. A standard 30-amp system cannot handle the electrical load of two air conditioners running at the same time.
Choosing the Right BTU Size for Your Rig
Picking the right British Thermal Unit (BTU) rating is a critical decision. Go too small, and the unit will run constantly without ever cooling the space. Go too big, and it will cool the space so fast that it shuts off before it can dehumidify the air, leaving you with a cold, clammy feeling.
As a solid rule of thumb, a 13,500 BTU unit is sufficient for most RVs up to about 30 feet. If you have a larger rig, frequently camp in hot climates like Arizona or Florida, or have poor insulation, stepping up to a 15,000 BTU model is a smart investment.
Ducted vs. Non-Ducted Systems Explained
This is one area where you don’t have a choice—it’s determined by how your RV was built. You must replace like with like.
- Ducted Systems: A central rooftop unit pushes cold air through a network of channels hidden in the ceiling to multiple vents throughout the coach. If you have this setup, you need an AC and ceiling assembly specifically designed for ducted applications.
- Non-Ducted Systems: Often called “direct dump” or “chillgrills,” the air blows straight down out of the main air distribution box on the ceiling. They are simpler and common in smaller RVs or as the second AC unit in a bedroom.
If you are replacing an air conditioner in a ducted system, you must buy a ducted-compatible AC. A non-ducted unit simply will not connect to your RV’s existing vent network.
Ready to get this project done? RVupgrades.com has a massive selection of top-brand air conditioners, sealants, and every installation accessory you could need to get the job done right. Shop our collection of over 20,000 in-stock parts and get everything you need with fast, reliable shipping.
