Using and Maintaining Your RV
Keep the Cool--Maintain That A/C Unit
Russ and Tina De Maris

Summertime, and the livin' is -- hot, sweaty, and icky -- unless you've maintained your RV air conditioning unit. While the actual unit is in a shroud, there's no need for the subject to be shrouded in mystery.

What makes air conditioning work? The science is the principle of heat transfer. At the heart of it is a liquid refrigerant. Suffering from a split personality, the refrigerant is a liquid and also a gas. In the gaseous state, it readily absorbs heat. Put that gas under pressure, it becomes a liquid, and hey presto! The liquid refrigerant gives off the heat.

So how does it all work? Inside your RV, the unit has metal coils that absorb the inside heat. The gaseous refrigerant is pumped under pressure to the outside portion of the a/c box. There, in a liquid state, the heat is released to the air outside your rig.

The principle is simple -- and ozone safe. RV air conditioning units utilize "R-22" refrigerant, which does not contribute to holes in the ozone layer. You may not be completely off the hook, as some believe that R-22 may contribute to global warming. Since we like our atmosphere, and since the coolant system is under pressure, send your unit to a professional when the cooling system itself needs repair. Neverthless, there's plenty you can do to keep your cooler cool.

To keep the system in tip-top shape, give your air conditioner an annual "physical." It's easy, and you probably have the tools and equipment needed to give the system a once over. Here's a step-by-step:

Power Down: Turn off the shore power to the a/c unit. Most RVs have an electrical breaker in the panel box that serves the air conditioner -- switch it off and make sure the power is truly down by flicking the air conditioner unit off and on.

Inspect the Shroud: The plastic shroud protects the unit from weather, tree branches, bugs, etcetera. Being plastic, they are susceptible to wear, tear, and the forces of nature. Look for cracks and other damage. Mounting holes can develop cracks, and a shroud flying off the roof at freeway speed is sure to make an entry for your traveling journal. If damage is severe, a new shroud may be in order. Not cheap, but less than a new a/c unit. Consider replacing old-style plastic shrouds with fiberglass or metal after-market copies, if available.

Under the Hood: Remove the shroud screws and pop the top. Carefully dust off the evaporator fins. A shop vac with a brush tip is helpful, and be sure to suck out any leaves, needles, or other debris. Examine the tubing in the unit for cracks or evidence splits. You'll need a professional to fix this type of damage before you lose your coolant charge. Loose or discolored wires indicate a loose connection that needs tightening, and possibly replacing the damaged wire. Be careful! Starter capacitors can hold a charge for a long time! If you don't know the difference between a capacitor and a cow, or are unclear on how do safely handle them, get professional help. A good size capacitor can store enough wallop to literally blow you off the roof. 'Tain't pretty, but it's true.

Bent Fins: The small fins on the outside of the unit are easily bent. A tiny, carefully controlled screwdriver can straighten these fins out. An a/c unit repair shop may be able to sell you a fin-straightening comb, which will speed up the process.

Inside Inspection: Back in the coach, remove the inside grill and face assembly. Remove the air filter and clean or replace it. A buildup of dirt on a filter with a little water mixed in can make for a wonderful bouquet of mold and mildew stink. Your owner's manual will tell you if you can wash your filter. New filters can be had at an RV supply, but you may be able to cut one to size from stock at a heating and cooling supply for less.

While you have the cover off, check up to make sure the unit is "square with the world," in that the unit should sit in alignment with the hole in the ceiling. Generally four bolts hold the unit in place, check to ensure they're tight. Loosen and adjust alignment if needed.

If you see any evidence of water leakage, you probably need a new roof gasket. A square chunk of rubber, this seal lies between the a/c unit and the roof. Loosen the mounting bolts from inside, then carefully tip over the a/c unit onto its side from the roof. You may need to disconnect some wiring to do this. When you get the new gasket, be sure you obtain the correct sealant to use with the gasket.

Test that Beast: Unit back in place? Restore power and turn it on. Measure the air temperature at the filter grill, and then check the temperature of the chilled air pumped into the coach. Ideally you'll find a temperature differential between 18 and 25 degrees Fahrenheit. If less than 18°, have the unit checked out by an a/c technician.

Need cool ideas? Check out your owner's manual. Can't find it? Here's the generic instruction set.

First, Check Your Power Supply: Use a voltmeter and verify a.c. voltage is at least 108 volts. Try to run your a/c at less than that and you could burn up your motors. Then you'll really lose your cool.

1. Set the thermostat for the warmest setting

2. Switch controls to "low cool" or "low air"

3. Once the fan begins to run, turn the thermostat down to where the compressor engages and cold air begins to flow.

4. When the room temperature is at the desired point, readjust the thermostat upwards to where the compressor "cycles" off and on. Not allowing the compressor to cycle may cause the unit to block up with ice. You'll know when that happens, the compressor will run, but you won't get chilled air. Fix it by shutting the unit down until the ice melts.

I shut off the a/c and tried to restart it a short time later, but the compressor won't start. Compressors build up quite a bit of pressure, and quickly cycling them off and on can spell disaster. Hence, many a/c units have a built-in timer that mandates a 3 to 5 minute rest period between compressor cycles.

My shore power cord isn't quite long enough to reach. Can I use an extension cord? Much depends on how much power is available from your hookup. 15 amp circuits will probably provide only enough power for a small unit. A 13,500 Btu unit needs nearly 20 amps to start, and 15 amps to run. You'll be pushing your 15 amp service hard to start, and you'll have no juice left over for anything else.

Extension cord? To safely pump 20 amps, a cord with 10 gauge conductors can carry you 27 feet. Run 30 amps and your 10 gauge cord can be no longer than 17 feet. If in doubt, leave the extension cord out!

What's a heat strip? This is a small built-in heating unit, designed not to heat, but to take the chill off the air on a cold day. Some units can have a heat strip added after the fact, but regardless, you'll still need your LP heat.

A few a/c units use the thermostat to control the heat strip; most are "off or on."

Keep it clean. Keep it maintained. Keep your cool.