How Can I Monitor My Air Conditioner Run Time?

Watch the Clock

• The best way to monitor the run time of your air conditioner is to have a seat somewhere near to where you can hear the system turn on and off. Grab a stopwatch. You don’t necessarily need to know the exact time down to the tenth of a second, but have a timekeeping device to keep casual track of the run time of your system. Start the timer when the system kicks on and stop the timer when it turns off. If it is running normally and at peak efficiency, you will find that the run time is generally between 10 and 15 minutes per cycle. The time in between cycles may vary based on insulation and other factors in and outside the home. The air conditioner needs to cool the air, as well as remove moisture to do its job properly, and the 10- to 15-minute window is usually how long it takes to do both.

It Runs Too Long

• If your experiment indicates a run time that is significantly longer than 15 minutes, then you have a reason for concern. You may be wasting considerable energy because of an undersized system. When a system is not producing enough British thermal units, or Btu, to cool the home and dehumidify it within 15-minute cycles, then it runs excessively. The undersized unit will run a long time or even constantly to try to keep up with the demands of the thermostat. You’ll see a major hike in your utility bills in this instance.

It Short Cycles

• Short cycling can be as much of a problem as long cycles, if not more. When the air conditioner runs cooling cycles that are very short, meaning the system kicks on and off in less than 10 minutes, it could mean that the system is too large for your home. Bigger is not necessarily better in air conditioning. The house cools so quickly with an oversized unit that it doesn’t have time to remove the moisture, leading to a cold and clammy feeling inside. In addition to the comfort factor, the system’s frequent on-and-off cycles will wear out the equipment too fast, resulting in the need for premature replacement.

Variable Run Time

• There are exceptions to the 10- to 15-minute rule, of course. Run time in air conditioning systems varies as a result of several factors. During times when the weather is exceptionally hot outside, the air conditioner simply has to work a little harder to keep up. Likewise, during a house party with lots of people in the home, it may have to run longer to compensate for the additional heat. The same goes for times when there is a lot of cooking going on in the house. These activities also add moisture to the air, so longer cycles are actually preferable. The variance should be temporary, though.

Lesser-Known Cause

• A lesser-known cause of longer run times in your air conditioner is galvanic corrosion. This happens when the copper in the system tubing and the aluminum in the cooling coil react to corrosives in the environment, such as acid rain or fertilizers that get into the outside unit. The aluminum leaches into the copper. This galvanic corrosion causes the coil to deteriorate and lose surface area gradually until the ability to move cool air through the system is reduced enough to lengthen the necessary run times to compensate. This is usually only a noticeable factor with systems that are many years old.