How to Put Freon in an RV Rooftop Air Conditioner

by John Cagney Nash
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The air conditioner works by passing air over an evaporator coil, which is cooled by the use of a refrigerant. The most common refrigerant is Freon, a brand name owned by DuPont that is universally--albeit mistakenly--used as a generic term. A drop in the level of refrigerant translates into a drop in the machine's efficiency. Rooftop units do not typically have a user-serviceable port, almost always being systems sealed at the factory. To put Freon in, a charging port would have to welded into the system by an expert. It is possible to put Freon into some RV rooftop air conditioners.

Step 1

Release and lift away the rooftop air conditioner's outer shroud. The shroud will be held in place by a series of fasteners around its lower rim. Use a screwdriver or socket or wrench, as determined by the fasteners used by the manufacturer. When lifting away the case, take care not to contact the fragile equipment inside.

Step 2

Inspect the machinery to learn whether there is a refrigerant port. If there is, it will be located on the side of the machine that contains the larger of two copper tubes, which runs from the compressor to the RV's interior and the evaporator coil. This is called the "suction" side of the system.

Step 3

Consult the manufacturer's literature or a data tag on the machine to determine which type of refrigerant is required. Older vehicles typically use R22, which is now expensive and difficult to source. Newer vehicles use a number of different types. Buy a recharge kit of the appropriate refrigerant.

Step 4

Use your thermometer to measure the ambient temperature inside the RV. Locate the air conditioner's chart, which will typically be fixed inside the shroud. The chart will have a series of temperatures noted alongside a series of optimum refrigerant pressures, one for each temperature specified.

Step 5

Attach the manifold gauge hose clearly labeled as being for the suction side to the port, usually the left-hand hose. Attach it by screwing the female hose end in a clockwise direction onto the male threads of the port.

Step 6

Switch the air conditioner on by activate it by dropping the thermostat to its coldest setting.

Step 7

Consult the gauge clearly labeled as being for the suction side to confirm that a top-up or recharge is necessary. Do this by reading the pressure of the refrigerant inside the air conditioner and comparing it to the chart's ambient temperature figure, which matches your reading from inside the RV. If the refrigerant pressure is less than optimum for the temperature measured inside your RV, it is necessary to top up or recharge the system.

Step 8

Attach a container of the prescribed refrigerant to the hose clearly labeled as being for this purpose, usually the central hose. Purge the gauges by briefly opening and closing the valve clearly labeled for this purpose, usually the right-hand valve.

Step 9

Open the clearly labeled charge valve and allow Freon to enter the air conditioner for one minute. Close the valve and wait a further minute before rechecking the gauge. Repeat this process as necessary until the refrigerant pressure reaches the level specified as optimum for the temperature measured inside your RV.

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