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What’s Causing Your AC Unit to Short Cycle?
What’s Causing Your AC Unit to Short Cycle?
Most homeowners don’t pay too much attention to their air conditioners they expect them to turn on when it gets too hot in their homes and turn off when it’s back to a comfortable temperature.
But it can be hard to ignore when an AC seems to be turning on and off very frequently. This is what’s known as short cycling. A properly functioning central AC will turn on and off 2-3 times an hour, or every 15-20 minutes. If your AC is turning on and off every 10 minutes or less, it’s likely short cycling and you could be putting unnecessary stress on your HVAC equipment, leading to:
- High energy bills
- Inconsistent temperatures
- Increased indoor humidity
- Shorter system lifespan
Here are the top causes of short cycling issues and what to do about them.
1. An Oversized System
When it comes to HVAC systems, proper sizing can make a big difference in AC performance. If your HVAC system is too big for your home, it won’t run long enough to evenly circulate conditioned air, leaving hot and cold spots in your home. It also won’t effectively remove humidity from your indoors, which can be a dealbreaker for many homeowners on a humid Pittsburgh summer day. Here’s part of the problem:
Rapid Cooling: An oversized system cools your home too quickly. This means it reaches the desired temperature on the thermostat before it has had enough time to run a full cycle. As a result, the system shuts off prematurely, only to turn back on again shortly after as the temperature rises.
Poor Humidity Control: AC units not only cool the air but also dehumidify it. When a system is oversized, it cycles on and off so rapidly that it doesn’t have enough time to remove moisture from the air effectively. This can leave your home feeling clammy and uncomfortable even though it’s cool.
Increased Wear and Tear: Short cycling puts additional stress on the AC components, leading to increased wear and tear. This can shorten the lifespan of the system and lead to more frequent breakdowns.
Higher Energy Costs: While it might seem counterintuitive, an oversized system can actually increase your energy bills. The constant on-and-off cycling consumes more energy than a properly sized unit that runs for longer cycles.
Unfortunately, if your AC unit is too big you can’t “fix” it it needs to be replaced. The good news is that you’ll immediately start saving money with new, properly-sized HVAC design and installation services.
2. A Clogged Air Filter
If you don’t change your air filters regularly, they could collect so much dirt, dust, and particulates that they restrict airflow through your system, causing your AC to short cycle. The good news is that air filters are easy to change—they’re also a part of an AC maintenance visit!
A dirty air filter restricts airflow to your AC unit. This reduced airflow causes a few issues that lead to short cycling:
- Overheating: The AC system relies on airflow to cool its internal components. When airflow is restricted, the heat generated by the system can’t dissipate properly, causing it to overheat. Most AC units have a safety mechanism that shuts off the system to prevent damage when it gets too hot.
- Frozen evaporator coils: The evaporator coil is responsible for cooling the air that blows into your home. Restricted airflow can cause the temperature around the evaporator coil to drop too low, leading to ice buildup. This ice further restricts airflow and can cause the system to shut down.
- Increased pressure: Restricted airflow can also cause pressure to build up within the system. This can trigger the high-pressure limit switch, a safety mechanism that shuts down the unit to prevent damage from excessive pressure.
A dirty air filter starts a chain reaction that leads to overheating, frozen coils, or increased pressure, all of which can trigger safety mechanisms that shut down the AC unit prematurely, resulting in short cycling.
3. Low Refrigerant
Refrigerant is the “lifeblood” of your AC it’s how your cooling system transfers heat out of your home and lowers the temperature inside. If you have a refrigerant leak and you’re running low, your system will have to work harder to remove heat from the air and can short cycle.
- Reduced Cooling Capacity: Refrigerant is the substance that absorbs heat from your indoor air, making it colder. When refrigerant levels are low, the system’s cooling capacity is diminished. This means it takes longer for the AC to reach the desired temperature on your thermostat.
- Increased Strain on the Compressor: Low refrigerant levels force the compressor, the heart of your AC system, to work harder to compensate for the lack of cooling power. This increased strain can lead to the compressor overheating and shutting down prematurely, causing short cycling.
- Frozen Evaporator Coils: As the refrigerant level drops, the pressure within the system decreases. This can cause the temperature of the evaporator coil to drop below freezing, leading to ice buildup. Ice on the coil further restricts airflow and exacerbates the short cycling problem.
Why does refrigerant get low?
- Leaks: The most common cause is a leak somewhere in the refrigerant lines. Leaks can occur due to wear and tear, corrosion, or damage to the lines.
- Improper Installation: If the AC system wasn’t installed correctly, it may have been undercharged with refrigerant from the beginning.
- Age: Older systems are more prone to developing leaks.
Anytime you have a refrigerant leak, you need to call an HVAC professional to fix the leak and recharge your refrigerant.
4. Frozen Evaporator Coils
Without regular HVAC maintenance, dirt and dust can build up on your AC unit’s evaporator coils. This makes it more difficult to absorb heat from the air, and condensation can freeze on your coils, causing your AC to short cycle or even shut off completely.
- Restricted Airflow: The evaporator coil’s job is to absorb heat from the indoor air. When airflow across the coil is restricted, the temperature of the refrigerant inside the coil drops too low. This causes the moisture in the air to freeze onto the coil, forming a layer of ice.
- Further Restriction: The ice buildup further restricts airflow, creating a vicious cycle where the coil gets colder and the ice layer grows thicker.
- System Shutdown: Eventually, the ice buildup becomes so severe that it triggers a safety mechanism in the AC unit, causing it to shut down to prevent damage.
- Thawing and Restart: Once the ice melts, the unit may restart, but the cycle will likely repeat if the underlying cause of the airflow restriction isn’t addressed.
Yearly AC tune-ups are one of the most cost-effective ways to avoid expensive air conditioner repair and extend the life of your unit.
5. Your AC Is Too Old
Nothing lasts forever and that includes your cooling system. Eventually, years of operation will slow down its efficiency and cause the wiring to become loose or worn out, leading to short cycling.
- Wear and Tear on Components: Over time, the various components of an AC unit, such as the compressor, fan motor, and capacitors, will wear down. This wear and tear can reduce their efficiency and make them more prone to overheating or malfunctioning, which can trigger short cycling.
- Refrigerant Leaks: Older units are more likely to develop leaks in the refrigerant lines. Low refrigerant levels can cause the system to cycle on and off frequently as it struggles to maintain the desired temperature.
- Electrical Issues: Aging wiring and connections can become loose or corroded, leading to electrical problems that disrupt the normal operation of the AC unit and cause it to short cycle.
A qualified AC technician can assess your system and explain how you may or may not benefit from a new, high-efficiency AC unit. Upgrading your HVAC often leads to fewer breakdowns, lower energy bills, and a more comfortable home!
6. Direct Sunlight
Direct sunlight can contribute to short cycling in a few ways:
- Overheating the thermostat: If your thermostat is located in direct sunlight, it may register a higher temperature than the actual room temperature. This can cause the AC unit to cycle on and off more frequently as it tries to cool the room to the set temperature, even though the room may already be cool enough.
- Overheating the condenser unit: The condenser unit, located outside, releases heat from the refrigerant. If the condenser is exposed to direct sunlight, it has to work harder to dissipate the heat, which can lead to overheating and potential short cycling.
- Increased internal pressure: The refrigerant in the AC system is sensitive to temperature changes. Increased heat from direct sunlight can cause the pressure in the system to rise. If the pressure exceeds the safety limit, the high-pressure switch will activate, shutting down the system to prevent damage.
To mitigate these issues, place your thermostat in a central area of your home, away from direct sunlight, windows, and drafts. Shade your outdoor condenser unit to reduce exposure, and call Calfo for regular maintenance!
7. Heat Generating Appliances
Heat-generating appliances can contribute to short cycling, especially if they are located near the thermostat or a poorly-ventilated area.
- Increased Room Temperature: Appliances like ovens, stoves, dryers, and even electronics generate heat when in use. This heat can raise the temperature of the room, causing the thermostat to trigger the AC to cycle on more frequently. If the heat source is powerful or the room is small, the AC might struggle to keep up, leading to short cycles as it constantly turns on and off to maintain the set temperature.
- Thermostat Placement: If the thermostat is located near a heat-generating appliance, it may sense the appliance’s heat and inaccurately register a higher room temperature. This can cause the AC to cycle unnecessarily even if the rest of the room is cool enough.
- Additional Strain on the AC Unit: Heat-generating appliances create an additional load on your AC unit. The AC has to work harder to remove the extra heat, which can lead to overheating and potential short cycling if the unit isn’t properly sized or maintained.
How can you mitigate these issues?
- Strategic Appliance Placement: If possible, place heat-generating appliances away from the thermostat and in well-ventilated areas. For example, use exhaust fans in kitchens and bathrooms to remove excess heat and humidity.
- Proper Thermostat Placement: Ensure your thermostat is located in a central area of your home, away from direct sunlight, drafts, and heat sources. Consider relocating it if necessary.
- Regular AC Maintenance: Keep your AC unit well-maintained by scheduling professional inspections and tune-ups. This will help ensure it’s operating efficiently and can handle the additional load from heat-generating appliances.
- Use Appliances Strategically: Try to use heat-generating appliances during cooler parts of the day or when you’re not relying on your AC as much.
How Many Cycles Per Hour Are Ideal For My AC Unit?
Ideally, your AC unit should have regular cycles 2-3 times per hour, with each cycle lasting about 15-20 minutes. However, several factors can influence the number of cycles:
- Outdoor Temperature: On hotter days, your AC will need to run more frequently to maintain the desired indoor temperature.
- Thermostat Settings: If you set the thermostat to a very low temperature, your AC will cycle more often to reach that temperature.
- Size of Your Home: Larger homes require more time to cool, which can result in longer cycles.
- Insulation: Well-insulated homes retain cool air better, leading to less frequent cycles.
- Efficiency of Your AC Unit: Newer, more efficient units may have longer cycle times than older models.
If your AC is cycling more than 3 times per hour consistently, it could indicate an issue such as a dirty air filter, refrigerant issues, or a problem with the thermostat.
On the other hand, if your AC is cycling less than 2 times per hour, it might be oversized for your home, or there could be an issue with the airflow or thermostat calibration.
If you’re concerned about your AC’s cycling frequency, it’s best to consult an HVAC technician. They can diagnose the problem and recommend the appropriate solution.
Schedule AC Services Today from Pittsburgh’s Finest
At Calfo, we roll out the red carpet (literally!) for every one of our customers, whether you’re calling for routine maintenance, AC unit repair, or new AC installation . Our technicians have at least 10,000 hours of training, so no matter what the issue with your cooling is, the team at Calfo can help!Get your home’s HVAC system back on YOUR schedule. Call or contact Calfo online for help with a short cycling AC and much more.
