In addition to handyman skills, this do-it-yourself project requires some heavy lifting and maneuvering, made easier by a helper.
By Mark Quasius, F333630
Air conditioners are essential luxuries in motorhomes. They keep us cool and comfortable when it’s hot outside so we don’t have to rough it. And although modern air-conditioning units are fairly well built, they do lead a tough life. On the roof, they are subjected to the hottest heat that the sun can dish out. They also can be damaged by tree branches when the coach is maneuvered into a tight campsite, and they just love to pick up moisture that can lead to rust. Add in the constant vibration and pounding from the road, and you can see why the air-conditioning unit doesn’t exactly have the best seat in the house. After all, would you want to ride up there?
Like any component in an RV, especially those with movable parts, air conditioners don’t live forever. Eventually, you will have a failure. Minor items, such as starting capacitors, can be replaced, but the air conditioner itself is generally not serviceable. No valve tap ports are available for checking the refrigerant charge. If the unit doesn’t perform, you would have to cut and solder taps into the system, which isn’t cost-effective and may not even solve the problem.
Fortunately, air conditioners aren’t all that hard to replace. You’ll need a few basic tools, some reflective foil tape, and some caulk. The hardest part is getting the new unit up on the roof.
Air conditioners are designed to fit a 14-inch-square hole in the roof. That is the industry’s standard roof vent size, which makes replacement much easier. Some units drop the air straight through the roof and ceiling directly into the RV’s interior; in others, air passes through ducts before entering the RV’s living areas. Both systems use the same 14-inch-square hole in the roof, and the air conditioner is secured with four mounting screws. Power generally is run through the ceiling to the opening.
We found a motorhome with a ducted unit that failed after seven years of heavy use in the Texas Hill Country. After performing some initial tests on the system, we discovered that the compressor had a locked rotor and had seized up, so a new unit was needed. A quick search online found an exact replacement; we ordered it, and it arrived a few days later.
Out With The Old
The first step was to switch off the circuit breaker that supplied the 120-volt-AC power to the air conditioner, so that it was safe to work on. The thermostat also was switched to the “off” position. The next step was to take out the existing unit, starting with the fiberglass cover. Four screws that hold the cover in place were removed, and we tossed the cover over the side of the motorhome.
In most air conditioners, electrical connections and components are inside the cool air plenum to help keep them cool as well. To disconnect these, it was necessary to remove the sheet-metal cover from the plenum. The plenum joints were taped, so we used a utility knife to cut the tape at the joints. The sheet-metal screws then were dug out from beneath the tape so that they, too, could be removed. Once the screws were out, the sheet-metal cover was lifted off and laid to the side. The 120-volt-AC wires were disconnected at a modular coupler. The entire control box was connected to the thermostat with a number of low-voltage connections and was secured to the sheet metal via two wing nuts. The connection between the air conditioner’s compressor motor and the control box was a modular plug, so we simply unplugged it, removed the two wing nuts, and put the control box down into the plenum to get it out of the way. A temperature sensor probe that had been inserted into the evaporator coil also was removed.
Some units have a diffuser in the ceiling. The diffuser must be removed from the interior ceiling, and then the four through bolts that hold the air conditioner to the roof must be removed. But because this unit had a ducted ceiling, we did not have to deal with an internal diffuser panel. Instead, four hex-head lag screws had been installed from the upper unit and tapped into the steel tube roof trusses to secure it. To keep these from loosening, as well as to prevent moisture intrusion, a glob of self-leveling caulk had been applied to the head of each screw. We scraped off the old caulk, removed the four screws, and slid the old air conditioner out of the way. The rooftop beneath the air conditioner had accumulated seven years’ worth of dirt, so it was thoroughly cleaned. Now the fun part began.
To get the air conditioner off the roof, we first placed a small extension ladder against the side of the motorhome. We attached a large tow strap to the framework of the air conditioner, which we slowly eased down the ladder. One person up top held back and fed the tow strap down, while a second person helped support the weight from the bottom and guided the unit down the ladder.
In With The New
After the old unit was safely down, it was time to bring up the new unit. The fiberglass shroud was removed, and the tow strap was attached to the frame of the new unit, which was hoisted up the ladder in the reverse manner of lowering the old unit down. Once the unit was up on the roof, one person could maneuver it into position. However, with the bulk and weight of the unit, having two people to ensure proper placement of the unit on the gasket might be best.
Next, the foil tape was cut and the screws were removed from the new unit. This allowed the sheet-metal cover to be removed to provide access to the front mounting holes, as well as the wiring.
The new unit’s foam gasket was designed to compress and seal the area around the access hole so that water cannot enter the RV’s interior. We set the unit in place and marked the location of the existing mounting holes; to match them, we had to drill into the new air conditioner’s baseplate. (On a design without ducts, that would not be necessary, because the four bolts run right through the access hole in the roof.) The four screws were then installed, taking care not to overtighten and distort the base. A dab of caulk was applied over each of the four mounting screw heads.
It is important that the air conditioner mounting bolts be properly torqued to the manufacturer’s specifications. In the absence of a torque wrench, the recommendation is to compress the roof gasket no more than 50 percent. Roof gaskets are 1 inch thick, and the mounting bolts are 1/4-inch x 20 threads per inch, so the bolts should be tightened 10 full turns each to prevent warping of the base pan. Warping can cause leaking, excessive vibration, and fan and/or compressor noise.
We retrieved the control box from the access hole in the roof plenum and laid it on the roof alongside the new air conditioner. The wiring was reconnected, and the temperature probe was placed into the evaporator core. The control box was attached to the sheet-metal cover with the two wing nuts, and the cover was reinstalled. After all of the sheet-metal screws were in place, we brought out our new roll of foil tape. All of the seams that we previously had cut were taped again to ensure a tight seal. We also ran tape over the screw heads to ensure that they would not loosen up and fall out.
Before reinstalling the cover, we switched the circuit breaker back on and tested the unit. Everything worked great, so we shut it down and reinstalled the cover. It should now be good for another seven years. And the money saved in labor costs can be put to better use buying fuel and driving the RV.