Not everyone enjoys the same temperature range, and that can lead to some ambiguity about the best time to turn off the AC system. You may find it also annoying to switch between heating and cooling in the late summer or fall when the temperature can sometimes swing wildly. Unfortunately, using your air conditioner at the wrong times of the year can potentially lead to costly future repairs.
The Effect of Cold Weather on AC Components
The major components of your air conditioner are all highly resistant to changes in temperatures, as long as you keep the unit turned off. You can provide your outdoor condenser unit with some extra protection by brushing off snow and ice, but it's unlikely to suffer any adverse effects over the winter. Likewise, the evaporator coils in your basement will shrug off cold winter nights.
This situation can change when you turn the system on, however. Your air conditioner relies on refrigerant moving through the system at the proper temperature and pressure. When the ambient outside temperature is too low, the refrigerant may not change state to a gas before returning to the compressor. Liquid refrigerant has the potential to damage or destroy your compressor.
Additionally, the compressor itself may not function well at low temperatures. Motor oil manufacturers design their product to flow more easily in cold weather, but the lubricating oil found in your AC compressor does not have similar properties. Turning the compressor on in freezing weather can rapidly wear out internal components due to a lack of lubrication.
Avoiding Cold Weather Damage
Fortunately, it's not easy to damage your air conditioner. Most modern air conditioners include ambient temperature sensors that prevent the compressor from engaging below a specified temperature. This setpoint is generally around 60 degrees Fahrenheit. In other words, don't be surprised if your air conditioner fails to turn on at all during the winter!
If you want to stay on the safe side, then it may be a good idea to switch your thermostat to "heating" mode once temperatures consistently drop below this level. If you experience significant temperature swings from day to night, avoid using your thermostat's combined heating and cooling mode. Disabling this setting will prevent your AC from engaging on cold nights.
While most manufacturers do not design residential air conditioning units for cold weather operation, the likelihood of damaging one this way is relatively low. By switching your system from "cooling" to "heating" mode once fall weather rolls around, you can guarantee that your system won't accidentally switch on when the temperatures begin to fall. If you need more help preparing your air conditioner for fall, contact an HVAC contractor in your area.