Chill Out – Inside
Chill Out - Inside typography
man with towel wrapped around neck looking at thermostat
Kool RV’s DIY-friendly A/C Connect “turbocharges” ducted rooftop air-conditioners for better air flow and more efficient cooling — and reduces noise.
By Bill Gehr / Photos by the author
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taying cool inside an RV is a prerequisite when traveling in hot weather, but it’s oftentimes easier said than done. While no one wants to endure a hot interior — especially when it comes to getting a good night’s sleep — an RV is essentially a big tube made of fiberglass, metal and glass, so it shouldn’t come as a surprise when temperatures inside that tube rise dramatically while it bakes under a hot summer sun.

And, while rooftop air-conditioners are commonplace on RVs today, their inherent design tends to limit effectiveness — especially on triple-digit afternoons. That’s why we’ve tested different add-on aftermarket products designed to maximize the efficiency of stock A/C units; we want to stay cool, too.

One of the newest products to address this situation is the A/C Connect from Kool RV (koolrv.com). The add-on product is claimed to elevate current air-conditioners to their full potential, bringing down the temperatures inside while curtailing some of the noise.

To understand why rooftop air-conditioners don’t perform better, you have to look at how these units are installed and operate. Most RV manufacturers have a set way of building ducted systems to distribute the cold air, using pathways through the ceiling that can be inefficient and zap the air-conditioner’s potential. For starters, there are typically too many right angles that slow down the cold air pressure. Add to that, intense heat from the sun is only an inch or two above the ducted pathways, allowing for heat intrusion that warms the flow of cool air.

KoolRV A/C Connect device
The KoolRV A/C Connect is a simple device that is comprised of a molded plastic housing that fits in the discharge port of the plenum and has two flexible hoses attached to adapters that connect to ceiling duct inlets.
removing the ceiling assembly using a power drill
The first step was to remove the ceiling assembly, like the one in the project motorhome. Figure on removing four to seven screws, depending on the brand and model of air-conditioner.
person disassembling floor plate and divider
person disassembling floor plate and divider
Once the floor plate and the divider between the return air cavity and plenum are removed, the cavity for the return air becomes 40% larger in most air-conditioners. Both these parts will be discarded.
bolts being removed with a power drill
Four bolts through the hold-down ring were removed for better access to the ducting. It might be possible to leave these bolts intact during the installation, depending on clearance needed to modify the duct openings.
reinforcement brackets being removed
In this motorhome, there were reinforcement brackets installed in the duct opening. These brackets interfered with the installation of the A/C Connect and were pulled out and discarded.
dry run being done to figure out how the duct openings would have to be modified
Before cutting the duct openings, a dry run was done to figure out how the duct openings would have to be modified.
Making matters worse is plenum inefficiency. Here, the air-conditioner’s blower sends the cold air down into the plenum — directly onto a metal plate in the ceiling assembly that causes air pressure to cavitate and swirl as it’s forced into a duct on either side of the plenum. As the air expands, it creates a small amount of heat via the pressure caused by the cavitation. The cold air is forced into the ducting through 90-degree turns (or a tee with two 90-degree turns) that slows the pressure down further. Because of the limited space in the 14- by 14-inch square cut out area in the roof, the amount of return air pulled from the room and forced through the evaporator is limited, as well.

Over the years, creative owners would use pieces of foam that were fit into that area to help direct the air flow into the ducting rather than down to the ceiling plate. It was a rather crude solution, but it actually improved efficiency. KoolRV’s A/C Connect mounts in the rectangular exit from the blower and into the plenum to eliminate turbulence and distribute 100% of the cool air. The design of the A/C Connect also increases the return-air cavity by 40%, which translates into cooler air going through the evaporator — more air in, more air out.

The A/C Connect is surprisingly simple-looking but there was a lot of thought (from personal RV experience) and research that culminated in an adapter that is made of 3D-printed plastic and heavy-duty flexible hoses. The device can be easily manipulated to fit tightly into the plenum and rectangular ducting inlets; the company supplies aluminum ducting tape that can be used to completely seal off any holes or cavities that cannot be predicted when performing the install. The flexible hoses compensate for differences in ceiling ducting techniques and locations used by RV manufacturers. The company also provides a fitment list of A/C Connect adapters, depending on the brand and model air-conditioner.

measuring the adapter using a measuring tape
close-up of the tape measure on the adapter
The adapter was measured to determine how much duct-inlet foam would have to be cut.
tape measure against the duct openings
tape measure against duct opening
For some reason, the duct openings in this motorhome were designed poorly. Here two holes were cut rather than opening the entire duct on both sides. This made no sense since it restricted the air flow dramatically.
For this project, the A/C Connect unit was installed on a Coleman Mach 8 Series air-conditioner in a motorhome; the procedure is similar for other brands and models. Once the ceiling assembly is pulled down, which may require the removal of four to seven screws, the divider between the plenum and return air cavity is removed and discarded. The body of the A/C Connect simply snaps into place, while the plastic adapters attached to the flexible hoses are matched up with the duct openings in the ceiling. The plastic components at the end of the flexible hoses have different configurations — one has a flange and the other does not — to accommodate differences in the duct openings. If necessary, the flange can be cut off. In this case, it was rotated by holding the hose and twisting the flange. Also, the Styrofoam duct openings had to be trimmed, which is a simple procedure. The aluminum tape was used to seal potential air leaks.

It was necessary to remove two of the tie-down bolts that run from the plate around the opening in the ceiling and secures the air-conditioner to the roof. This was to make sure the flexible hoses would clear the bolts. After ducting fitment, the bolts were reinstalled; there was ample room to prevent hose abrading. Tip: While you’re in there, use a bright flashlight to inspect the return air cavity at the evaporator to ensure the area is free of dust and oils.

folding knife being used to cut open the ducts
Cutting the opening in the ducts was a simple matter using a common folding work knife. The Styrofoam was easy to cut. Just this procedure alone was destined to improve air flow.
close-up of the A/C Connect
The A/C Connect was designed to snap into the opening of the plenum without the need for tools. It must be pushed hard to make sure it is secure in the opening.
removed bolts
While positioning the A/C Connect, it was determined that the two hold-down bolts in plenum might interfere with the routing of flexible hoses. Rather than take a chance, the bolts were removed and reinstalled after the flexible hoses were in place. It’s important to keep these bolts away from the flexible hoses to prevent abrading the material.
pointing at the lip on the ducting adapter
The ducting adapter has a lip (flange) on one side to allow for a proper fit in the ducting. This lip will only fit in one way and can be rotated in the flexible hose, if necessary.
With the ceiling assembly back in place, it was time to compare results. I ran the air-conditioner one hour before the installation, tracking temperature, humidity and time to reduce temperatures: outside temperature was 86 degrees F. A thermometer was placed on the table right under the air-conditioner’s ceiling assembly and a pencil type air-conditioner thermometer was placed in the farthest register.

Within 16 minutes, the humidity was lowered from 40% before the installation to 28% after. Temperature from the farthest register dropped 8 degrees compared to the stock A/C performance and the air felt colder. Inside temperature was definitely more comfortable. One thing to keep in mind is that other model air-conditioners may be configured differently in the plenum and may not produce the same results; the company claims that customers can expect at least a 6-degree drop in temperature at the ceiling registers.

fitting the hose through the duct opening
Another dry run verified the adapter on the end of the flexible hose would fit in the duct opening. For this installation, the adapter had to be rotated 180 degrees.
view of duct tape sealing the adapters
Two rolls of aluminum tape were supplied in the kit. This tape was used to completely seal and retain the adapters in the foam duct openings.
view of the air ducts
In the end, it was obvious that the return air cavity and routing into the ducts were much more efficient. Before, cavitation restricted air flow into the ceiling ducts, impacting the distribution of cool air throughout the motorhome. Cooling efficiency was improved dramatically — according to KoolRV, users can expect up to 50%, depending on the make and model of air-conditioner and the ceiling ducting system.
air conditioning thermometer inserted through a vent
air conditioning thermometer inserted through a vent
An air-conditioning pencil-style thermometer was inserted into the farthest register from the air-conditioner. Before the installation, the air temperature at this register was 50 degrees; after the temperature was decreased by 8 degrees — a marked improvement in cooling efficiency.
Air flow was tested at the registers using a small strip of toilet tissue near one of the registers before and after; there was no question that air flow was stronger. Also, noise level dropped 3 decibels.

The simplicity of the installation is impressive, as is the quality of the A/C Connect components. The real payoff on the $84.95 investment and maybe 1 ½ hours of time can easily be measured by a marked improvement in comfort level. And your body will thank you.