Dometic FJX4 vs FJX7 Air Conditioner: Which is Best?

Aug 12, 2025

Sweating in your van like a rotisserie chicken? Time to upgrade your caravan or motorhome air conditioning. TL;DR: FJX4 is best for small rigs and boondocking; FJX7 wins for big RVs and brutal heat. Want the full scoop (with jokes)? Keep reading—we tested the breeze so you don’t have to.

Compressor Technology and Efficiency

Fixed-Speed vs. Inverter Compressor

Both the Dometic FJX4 and FJX7 series use fixed-speed compressors. These systems are reliable and consistent for cooling RV interiors. However, they don’t offer the variable output and fine-tuned control seen in inverter models. That said, the FJX7’s compressor is more powerful overall, giving it a clear performance edge.

Dometic rooftop air conditioner displayed on a white background.

Impact on Energy Consumption

The FJX4 is more energy-efficient thanks to its smaller cooling capacity. It uses less power and puts less strain on your electrical system. This makes it a top pick for owners who want to conserve battery life or run off solar. The FJX7, while more capable, does draw more power—especially in hot weather.

Power Requirements and Low-Amperage Campgrounds

Because of its higher output, the FJX7 needs a beefier generator. It’s less suited to low-amperage campgrounds unless you've upgraded your electrics. In contrast, the FJX4 works well with smaller generators and standard hook-ups. It’s the better option for those who travel off-grid or stay in parks with limited power access.

Performance and Noise

Cooling and Heating Power

The FJX4 provides 13,500 BTUs, ideal for areas up to 250 square feet. The FJX7, with 17,000 BTUs, is built for larger rigs and more demanding conditions. It cools faster and holds stable temperatures in hot, dry, or humid environments. Both models perform well, but the FJX7 has a clear upper hand in extreme climates.

How Compressor Type Affects Noise Levels

Although it has a more powerful compressor, the FJX7 operates surprisingly quietly. This is thanks to its advanced acoustic engineering and refined sleep mode. On full blast, it’s a bit louder than the FJX4, but still manageable. The FJX4, by design, is slightly quieter overall during regular use.

Dometic air conditioner unit mounted on a motorhome roof, with trees and blue sky in the background.

Airflow and Distribution

Both models are engineered to provide strong airflow and balanced temperature distribution. The FJX7 pushes more air due to its size, which helps cool larger interiors faster. The FJX4 offers reliable airflow for smaller RV layouts. Whichever you pick, both ensure you won’t be stuck in a sweaty corner.

Features and Design

Smart Connectivity and Controls

The FJX7 includes smartphone control through a dedicated app. It also has a more advanced remote with extra settings. The FJX4 includes a simpler remote and no app support. Both offer programmable settings, but the FJX7 allows for more detailed scheduling and integration with modern RV systems.

Physical Dimensions and Weight

FJX4: 38.5 x 38.5 x 9.5 in, 105 lbs
FJX7: 40.5 x 40.5 x 10.5 in, 125 lbs

The FJX4 is lighter and compact—ideal for smaller caravans or limited roof space. The FJX7, while bulkier, is still easy to install with proper support.

Aesthetics and Air Distribution Boxes (ADBs)

Both units have low-profile rooftop designs that blend with most RVs. The FJX7 typically comes with a more premium air distribution box. This box includes better airflow control and sleeker interior styling. The FJX4’s ADB is simpler but functional.

Dometic air conditioner installed on top of a white motorhome driving through a rocky canyon road.

Which Dometic Air Conditioner is Right for You?

Choosing Between FJX4 and FJX7

The Budget-Conscious Buyer

For those keeping an eye on costs, the FJX4 is a smart choice. It’s more affordable to buy, cheaper to run, and easier on your batteries. You still get solid performance, just in a smaller package. Perfect for weekend warriors and smaller setups.

The Tech-Savvy and Comfort-Oriented User

If you’re after remote control, app integration, and rapid cooling, go for the FJX7. It’s built for full-timers, hot weather travel, and larger caravans or motorhomes. The features are worth the extra investment if comfort is your top priority.

Other content you might like:

Back to Caravan Blog