Indoor Blizzard

Photos by Bob Livingston

Dometic reaches a pinnacle in cooling performance and efficiency after an extensive redesign of its latest roof-mounted air conditioner

Air conditioning inside an RV has become a basic amenity that owners consider part of the standard-build landscape. Almost all RVs are equipped with at least one rooftop air conditioner, with others taking advantage of multiple units to cover more square footage. The challenge for RV manufacturers is to size the HVAC system just right, especially in units of fringe lengths where it’s a coin toss whether to add a second air conditioner, or even a third. Dometic, a primary provider of roof-mounted air conditioners for a very long time, has recently brought to market a new model, the Blizzard, featuring numerous improvements in exterior design, insulation and efficiency.

In the aftermarket, owners will likely swap out older models that have a hard time keeping interior ambient temperatures at comfortable levels or have simply failed from years of use. Issues that are typically addressed center around air distribution, fan noise and the inability to keep the temperature differential between inside and outside under control. After experiencing most of these maladies with the original air conditioner mounted in a 34-foot fifth-wheel, the factory-installed unit was replaced with a 15,000-Btu Blizzard NXT with heat pump to test the results of an aggressive R&D campaign by Dometic to change the paradigm when it comes to rooftop air conditioners.

Dometic’s newly released Capacitive Touch Thermostat with Bluetooth capabilities allows control of the air conditioner, heat pump and furnace from a smartphone or tablet.
Dometic’s newly released Capacitive Touch Thermostat with Bluetooth capabilities allows control of the air conditioner, heat pump and furnace from a smartphone or tablet.

The test fifth-wheel was fitted with only one air conditioner because its length put the decision to add a bedroom unit on the fence. Also, the owners elected to use the bedroom roof vent for a Fan-Tastic Vent fan, figuring the improved air circulation would be valuable during visits to primitive locations. That made the original air conditioner work really hard in hot weather, and the interior was never comfortable when the outside temperature exceeded 90 degrees Fahrenheit.

While a number of impressive assets were built into the original Atwood Air Command unit, air distribution through the network of roof ducting was rather puny. Fan noise for this model was exceptionally quiet, but the inability to completely cycle the fan in response to the thermostat set point was a deal breaker. So off it went to make room for the Blizzard.
Removing an existing air conditioner does not require a great amount of mechanical aptitude, but it does take some effort, which can be mitigated with a few tricks of the trade. Once the ceiling assembly and the four long bolts securing the air conditioner are removed and the wiring disconnected, the unit can be lifted off the roof.

1)

The ceiling-assembly shroud is removed to gain access to the hold-down bolts,

2)

which are removed to release the air conditioner from the roof.

3)

The return-air divider is removed from the ceiling assembly. It will not be used with the new air conditioner.

4)

The Molex connector, supplying 120-volt AC power to the air conditioner, is disconnected. The new air conditioner will plug into the existing connector.

5)

The thermostat and furnace trigger wires are identified and cut.

6)

The wires are bundled and secured so they won’t interfere when placing the new air conditioner in the vent opening.

7)

Pushing up on the air conditioner from the inside releases the gasket from the roof so it can be removed.

8)

Climbing rope is tied around the original air conditioner and used to guide it down the rails of an extension ladder.

9)

A second person helps stabilize the air conditioner until it reaches the ground.

10)

The same rope and extension ladder are used to hoist the new Blizzard, still in its box, to the roof.

11)

The air conditioner is maneuvered over the roof-vent opening.

12)

Available in black or white, the high-impact-polypropylene injection-molded shroud and base pan have been redesigned to eliminate bird nesting and protect against corrosion and rust. New styling presents a modern look.

13)

Once the air conditioner is in place, the wiring is completed ...

14)

... and secured to the wood frame in the ceiling opening.

15)

The previous air conditioner required four thermostat wires versus three for the Blizzard, making it necessary to note and color-code to the terminals on the thermostat circuit board.

16)

Long ¼-20 bolts are driven into the air conditioner to seat the gasket. The new gasket is softer and thicker, and can be damaged if the bolts are torqued too tightly.

17)

A few cuts are necessary to fit the return-air divider in the ceiling assembly.

18)

Once cut, aluminum tape is used to fill any gaps.

19)

The foam insulation is measured ...

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... and positioned before cutting ...

21)

... and the backing is peeled away so it can be applied to the side of the return-air divider. You get only one shot at this, since the adhesive is very sticky and almost impossible to remove without damaging. A tight seal is necessary to prevent the return and cool air from mixing, leading to decreased efficiency.

22)

Access and filter covers slide into the ceiling-assembly shroud ...

23)

... which is screwed into the ceiling. The new shroud is smaller, leaving unsightly holes in the ceiling material.

24)

Two-inch maple molding, found at a local building-supply store, is used to conceal the old holes and bunched-up material. Cuts were made on an inexpensive miter saw, which were less than accurate. Thinner molding that does not need to be removed to slide off the filter cover will be cut later and painted to match the ceiling.

25)

Two-piece panels provide access to the ceiling assembly and foam filter ...

(26)

... which should be checked monthly during regular use of the air conditioner. The filter can be cleaned with soap and water.

27)

The ceiling assembly has a modern and tidy look, and the slide mechanism for securing the panels works well.

Most service centers use a forklift to bring it down from the roof, but do-it-yourselfers must be more creative. We’ve learned the hard way over the years to limit wear and tear on our backs, and the system we use is simple but effective. A climbing rope is tied around the air conditioner, and while the person on the roof lowers the unit by sliding it on the rails of an extension ladder leaning on the side wall, another person guides it to the ground. The opposite process is used to hoist the new air conditioner — still in its box — to the roof where it can be unpacked and positioned over the 14×14-inch standard roof-vent opening.
The rest of the job is pretty straightforward and accomplished from the inside. It’s easy to center the air conditioner in the vent opening by pushing from the inside, and once that’s done, the next step is to wire it up. If a non-Dometic air conditioner is being replaced, the wiring takes some study. For this job, the Air Command thermostat required four wires, which were routed from the air-conditioner unit; the Dometic requires only three. Since the wire color-coding was not the same, we needed to assign individual wires for the 12-volt DC power, ground and thermostat, and label accordingly.

Connecting the wires at the air conditioner went with little fanfare, other than to pay attention to the new color-coding. Fortunately, the same blue trigger wires for the furnace were used, so there was no issue here. A single wall-mounted thermostat controls the furnace, heat pump and air conditioning, which is a convenient feature. Power for the Blizzard is via a Molex connector, which was the same for the previous unit, so it was a simple plug-and-play operation.

Wrapping up the project required positioning of the return-air compartment partition, which took a little fiddle time to fit properly. Minor modifications were made to ensure a tight seal, which were improved with the use of aluminum tape. It’s important that the return air does not mix with the cool air, or the ultimate temperature will be impacted. This process will be easier when swapping out another Dometic product. Once in place, stick-on insulation is cut to size and attached to the return air divider.

The new ceiling-assembly shroud is smaller than the original and very nice looking. Its three-piece design makes it easy to access the filter, which should be washed regularly. The only caveat was that the smaller dimensions exposed screw holes and some distortion in the ceiling material, which was unsightly. Our solution was to frame the shroud with maple molding found at a local building-supply store. It required miter cuts made on an inexpensive box with large tolerances, which were not perfect but concealed the evidence left by the previous shroud. A more refined fit will be made down the road.

While the new look of the high-impact-polypropylene injection-molded shroud and base pan is certainly snazzy, we were more interested in the overall cooling performance. The Blizzard was tested in temperatures that hit 100 degrees, and the results were impressive. Most notable was the improvement in air distribution through the roof ducting. The high-capacity 350-cfm blower sent out a strong flow of air throughout the system that was much greater than the original unit.

A number of design enhancements and technology advancements contributed to a big improvement in cooling comfort inside the fifth-wheel, even when the temperature hovered at triple digits for most of the day. Strategically placed foam insulation and an integrated blower housing minimizes heat transfer so cooler air is produced and maintained. Improvements to the evaporator, condenser, fan and blower wheel all helped with the overall positive experience.

Noise and vibration were also big considerations in the revamp of this product, and improvements to the base pan get a big portion of the credit. At low speed, the noise was noticeably reduced from previous Dometic models, and even on high it was still possible to hear the television without turning the volume to maximum. Energy-damping ribs in the base pan minimize vibration and noise, as do the density-optimized mounting blocks, which also provide a better water seal.

Other improvements include integrated plastic bird guards to eliminate nesting, a softer and thicker roof gasket that compresses easier for a better seal and an integrated drain pan for effective water drainage.

Dometic’s Capacitive Touch Thermostat does a good job of controlling the air conditioner, heat pump and furnace, and its digital readout is easy to program. A new Bluetooth version allows users to set up an app on their smartphone or tablet and control the HVAC functions remotely. The Blizzard NXT air conditioner is available in 13,500- and 15,000-Btu capacities, with the latter (test unit) retailing for $1,480. The thermostat sells for $45;
the Bluetooth model is $88.

Air conditioning is an important amenity for any RV, and Dometic hit the mark with its design overhaul from both visual and performance standpoints. Owners will appreciate the Blizzard’s cooling and power efficiency, and enjoy the indoor experience, even when outside temperatures soar.

Dometic | 800-544-4881 | www.dometicusa.com


 

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