Roof-Mounted AC Freezing UP
Although there are many variations of air conditioners in Prevosts, the roof-mounted unit is certainly among the most common. One problem that has plagued most of us at one time or another is "freeze-up". Common symptoms of this problem include reduced or no air flow on the inside of the bus even though the fan is running and water is dripping from the ceiling after the AC is turned off. The dripping water is caused by the thawing of the frozen moisture that accumulated on the evaporator and lines.
Unlike the residential window mounted units, roof mounted RV units sit in the ceiling of the living space and are more susceptible to the accumulation of moisture and vapors from cooking, bathing, and even breath expelled from the occupants. All these things affect the evaporator that is deep inside the AC. This is the component that the fan draws air through, where it is cooled, and then blows it back into the living area. The condenser is equally important. The condenser fins can be seen from the outside of the AC unit.
Although not a cure-all, there are a few simple things we can do to minimize the problem of freeze-up:
- Clean the intake filters often by removing the filter and blowing out with compressed air and/or washing with water. A dirty filter can easily cause a unit to freeze up.
- When you run the unit in "Cool" mode, keep the fan on High as much as feasible. This will help minimize freeze-up by moving more air through the evaporator.
- Set the thermostat to a reasonably moderate setting. If it is 100 degrees outside and you set the thermostat to 50 and leave the unit running for an extended period of time, it will probably freeze. Ideally, you should set the thermostat closer to the room temperature so the compressor will cycle and have time for accumulated moisture to thaw and evaporate between cycles. As the room temperature drops, continue to lower the thermostat. If you are going to leave the AC on for several hours while you are away, set the fan to "On" instead of Automatic. This will help to continue to disburse the moisture and frost even while the compressor is off. If the room temperature is 85 and you want it to be 73, then set the thermostat to 73 not 50. As a general rule, the AC cools no faster if it is set to 50 than if it is set to 70. It just drops the temperature lower! There are a few exceptions with high-end home/commercial units that have variable compressor and fan components. When we set it to 50 degrees, we normally forget about it until we realize it is 60 degrees in the room, and we are cold. We then we get up and set it back to 73 where it should have been to start with.
- If you are going to take a shower or bath or boil water, open a roof vent a little to allow some of the moisture to escape instead of being drawn into the AC units.
- Make sure you check that the condenser fins are clean and straight at least once a year. Dirt and leaves may accumulate on the fins and reduce cooling capacity. Bent fins can have the same effect.
Of course there are other reasons for freeze-up including bad sensors, bad fan/run capacitors, low freon levels and a few other things, but if you follow the suggestions above, you will have a much better chance of eliminating or minimizing the problem of freeze-up.
