Why does my AC keep shutting off suddenly?

If you’re a homeowner noticing that your air conditioning is shutting off and on every ten to fifteen minutes, you’re probably wondering what’s wrong with your AC system. If your central air is starting up and shutting down for no discernable reason, this is known as short cycling.

What is Short Cycling in Air Conditioning?

Short cycling is a term used in HVAC to describe when a heating or cooling cycle shuts down prematurely, and the HVAC unit turns on and off frequently.

Air conditioning units are said to be short cycling when they turn on and off before they cool the environment to a desired temperature. For a variety of reasons, short cycling is problematic, as it causes higher energy bills, and unwanted wear and tear on the HVAC system.

Short cycling can be caused by defective parts, a dirty or poorly maintained system, or faulty components. Below, we look at the leading reasons for short cycling, and why your AC system inexplicably shuts on and off.

1. Thermostat is Faulty or Improperly Placed

The thermostat determines when your AC shuts off. If there is a malfunction with the thermostat, then the colling cycle will shut down prematurely. This can be caused by a problem in the thermostat itself or there is an electrical problem, like bad wiring to the thermostat.

Another way that the thermostat can cause your AC to shut down suddenly is if it is improperly placed. When the thermostat is placed away from windows, or near an air vent, or on the shady side of the house, it may incorrectly read that the house is cooled to the desired temperature.

2. Dirty Air Filters

Your air filters for your central AC should be changed about once a month during the warm summer months. When the air filters get dirty, and choked with dust and dander, the airflow is restricted. This causes the evaporator coils to freeze, which can cause the AC unit to shut down prematurely.

3. Frozen Evaporator Coils

The evaporator coil is inside your air handler, removing heat from the air inside your home. This cooled air is recirculated by the blower back through the air vents. When the evaporator coils get dirty, or if airflow is insufficient, frost and ice can form on the coils, causing the unit to shut down suddenly. The HVAC system must work harder to defrost the evaporator coil, causing wear and tear, as the unit overheats.

4. Condenser Coils are Dirty

The condenser coils are outside the home, and release heat to the outside during the summer. In a central AC system, these coils are in the outside unit, usually on a concrete slab, with fan-like fins on the top of the unit.

When the condenser coils are dirty, and coated with dust, debris, and grime, they can struggle to perform heat exchange properly. This can cause the unit to overheat and shut down prematurely.

5. Low Refrigerant Levels

Refrigerant is a substance that runs through the coils in the AC unit, and performs a heat exchange. In the warmer summer months, the refrigerant absorbs heat from inside your home, then dissipates it outside via the condenser coils.

When your refrigerant line has a leak, the heat exchange will struggle to function correctly. If you suspect there is a leaky refrigerant line, call a licensed HVAC contractor immediately. Ignoring a leaky refrigerant line can cause damage to the most expensive components in the HVAC system if ignored.

Please note that refrigerant should be self-contained in the line. There shouldn’t be a regular “topping off” of refrigerant. If the refrigerant is low, there is a leak in the like that must be fixed, or the problem will reappear.

6. Air Conditioning Unit is Oversized for Your Home

This can seem counterintuitive, but if your cooling system is sized for a much larger home than yours, it can cause short cycling. HVAC systems are built to remove a certain amount of heat from a certain amount of indoor space. When you have an oversized unit, it cools the home much quicker than it should, causing it to shut down quickly. However, your home heats up again quickly, causing short cycles where the AC runs for ten to fifteen minutes, then shuts down, then starts up again. Air conditioners are more efficient on energy when they keep the room at an even temperature.

7. Faulty Run Capacitor

Your AC system’s run capacitor has an important role. The run capacitor provides enough electrical current to turn your colling unit on, and it also provides enough power to keep the air conditioner running. When the run capacitor fails, power may only sporadically run to the air conditioning unit. This causes the AC system to turn on and off quickly. Another sign of a failing run capaicitor is that the AC system is not blowing cold air.

8. Your AC System has Electrical Problems

A common reason for a short cycling AC system is electrical problems. This may be caused by a bad connection, a broken thermostat, a faulty circuit board, a condenser or compressor not receiving power properly. To properly diagnose and repair the electrical issue, call a licensed HVAC contractor.

What are the Effects of a Short Cycling Air Conditioner?

It is possible for air conditioning systems to short cycle for weeks or months before the issue is fully detected. Perhaps you notice that the AC system is not blowing cold air, or you notice a pattern of the air conditioner shutting off after ten to fifteen minutes, and you need to do something to fix the situation.

While the AC system is short cycling, these cumulative effects are happening:

Increased humidity in your home. Your air conditioning unit removes humidity as well as heat from the inside of your home. When the AC system is short cycling, the humidity in the air remains inside. This can exacerbate condensation in humid local climates.

Higher energy bills. When your central air conditioner must work harder, it makes your electric bill rise. A short cycling heating and cooling system uses more energy than a perfectly functioning system, with less efficiency.

Wear and tear on your central AC system. Air conditioning units have a shelf life of about fifteen to twenty years, and when the unit is short cycling for an extended period of time, that wears down the compressor and condenser components.

How to Fix a Short Cycling Air Conditioning Unit

If you have gone through the checklist above, and none of things you can do easily are fixing the problem, contact a professional air conditioning contractor.

Professional Air Conditioning Repair in San Jose

If you need a licensed and bonded air conditioning contractor in the San Jose, Morgan Hill, or Gilroy area, Ventwerx HVAC is there. Since 2007, our team has helped homeowners with heating and cooling issues.

You can fill out a service request, or call (408) 422-2987 in San Jose or (408) 710-9595 in Morgan Hill for efficient and courteous heating and cooling service.