Help, My Air Conditioner Won’t Shut Off!

If your air conditioner won’t shut off, the temperature indoors quickly becomes too cool for comfort, and electrical power is wasted over the hours your air conditioner keeps running. Malfunctions affecting different system components can prevent the conditioner unit from shutting down as expected, such as a clogged air filter, a frozen evaporator coil, a faulty electrical relay switch, a dirty condenser coil, a constantly blowing fan, a bad thermostat, low refrigerant, and other HVAC system repair issues.

If you are unable to shut down your air conditioning system, Thomas & Galbraith offers a few tips to help. When air conditioners keep running despite your best efforts, call our team for professional service to diagnose and fix what’s wrong.

Is It Fine for Air Conditioners to Run Several Hours?

When outdoor temperatures are higher than usual, your air conditioner may cycle a bit longer than it does during milder weather. However, your air conditioner should never run for hours on end.

A cooling cycle should last approximately 15 to 20 minutes, and two or three cycles should run in an hour’s time. If you happen to have a cooling unit that is running longer, something is wrong within your HVAC system, and repair services are needed.

If your air conditioner is allowed to keep running for hours and hours, it’s wasting a great deal of electrical power. System components experience more wear and tear, leading to inefficient performance and defects that cause breakdowns. The damaged parts need to be replaced, increasing your repair costs.

Why Won’t My Air Conditioner Turn Off?

If you have an air conditioner that will keep running no matter what you do, here are the categories where we find problems:

1. Incorrect Thermostat Settings

Sometimes, it’s not that an air conditioner cannot turn off, it’s that it doesn’t simply because the thermostat isn’t correctly set. Temperature settings and fan settings are common culprits when a thermostat causes an air conditioner to stay on for hours at a time.

  • Most of us keep our homes at a preferred set temperature and know what that temperature feels like so we know when the air conditioner should turn off. If someone else in the home adjusts the set temperature downward, your air conditioner runs for a longer period and doesn’t turn off when you expect it will. The household thermostat war is a common reason your air conditioner still runs after you believe the set temperature has been reached.

  • If the system fan runs continuously, it may appear that the air conditioning is on all the time. However, it’s just the fan. If the fan has been turned to the ON setting, it runs all the time – both while a cooling cycle runs and in between these cycles. AUTO is the preferred setting which turns off the fan in between air conditioner cycles.

2. Bad Thermostat

Over time, a thermostat loses accuracy and experiences damage that disrupts communication with cooling and HVAC equipment. Dust and dirt build-up on temperature sensors, making it difficult for the thermostat to detect the temperature of the room. Wiring damage and loose electrical connections interfere with signals sent between the thermostat and air conditioner, which can cause the cooling system to run longer than necessary.

3. Electrical Problems

There are many electrical components that make up cooling systems. When a relay switch sticks in a closed position, the air conditioner receives constant power and continues to run. The contactor that supplies electrical power to the compressor can be damaged, causing the switch to stick closed and constantly feed electrical power to the outdoor unit. Sometimes it is possible to fix a switch that has become stuck, though often they need to be replaced to ensure the system works properly in the future.

4.  Stuck Fan Limit Switch

Correct fan settings are important to control the use of the system fan, but a malfunction of the fan limit switch can prevent the air conditioner from running the fan as instructed by the thermostat settings. If the switch sticks closed, the fan receives power all the time and continues blowing for hours, during and in between cooling cycles.

5. Dirty Condenser Coils 

The condenser coils in the outdoor unit release heat from the refrigerant that cycles through the coil after the compressor adds pressure. Surface area is needed to release heat, which is often restricted by dirt, dust, and grime that collects on the condenser coil. When the coil doesn’t have enough area to effectively release heat, the system isn’t able to cool the indoor air enough and will continue to operate as it tries to bring down the temperature.

6. Dirty Condenser Unit

The outdoor condenser unit itself needs to be free and clear of debris so air can flow through, passing over the condenser coils to help transfer energy from the hot refrigerant into the atmosphere. When leaves, mulch, grass clippings, and other matter collect on the condenser fins, not enough airflow makes its way through the unit, and heat transfer is restricted. This forces the air conditioner to keep running.

7. Frozen Evaporator Coils

Within the indoor unit, the evaporator coil pulls heat from the home’s air. Heating energy is absorbed by refrigerant inside the coils, which will make its way to the compressor and condenser coils to be released outside. When the evaporator coils don’t come into contact with enough heating energy, moisture can freeze on their surface which causes the air conditioning system to become frozen.

Dirt on the coil, poor air movement from a dirty air filter, or even a refrigerant leak can cause frozen evaporator coils. If the drain pan or condensate line is clogged below the evaporator coil, ice accumulation can be worse as there is more moisture in the system available to freeze on the coil.

8. Clogged Air Filter

With an air filter is completely clogged with pollutants, the air filter becomes restrictive, preventing air from moving freely through the air conditioner. Without ample air flow, the cooling system cannot cool air to the proper temperature, and will run for longer periods of time as it attempts to catch up with cooling demands inside the home.

9. Low Refrigerant

Each air conditioner is designed to hold a specific amount of refrigerant, which facilitates heat transfer through the cooling system. If refrigerant escapes through damaged coils, cracked refrigerant lines, or a defective expansion valve, the air conditioner is unable to absorb enough heat from the home’s hot air. The air conditioner will keep operating to bring the indoor temperature down, without much luck.

10. Fan Speed Too Low

The indoor blower fan can become bogged down by dirt and grime, which restrict its operating speed. If the blower fan cannot operate fast enough, the home won’t receive adequate cool air flow. When this happens, the HVAC system runs longer as it attempts to provide the cool air required indoors.

11. Air Conditioner Too Small

If an air conditioner wasn’t sized appropriately to meet a home’s cooling load, it will run for extremely long periods of time. Smaller air conditioners simply don’t have the power to cool spaces that are too large for the equipment. Undersized air conditioners waste a lot of electrical power and break down quicker due to excessive wear and tear from long run times.

How to Fix an Air Conditioner That Won’t Turn Off

If your air conditioner won’t shut off, try these quick and easy troubleshooting steps before you contact us for professional repairs by a NATE-certified air conditioner technician.

1. Change Thermostat Settings

Turn up the temperature so the thermostat is set a few degrees higher than the current room temperature. This setting should cause the thermostat to instruct the air conditioner to end its cycle.

2. Change the Fan Setting

As mentioned above, sometimes it’s only the system fan running and not the air conditioner, even though the fan’s operation makes it sound as if the cooling system is fully on. Make sure the thermostat is programmed to AUTO for the fan setting so the fan will not run in between cooling cycles.

3. Facilitate Good Air Movement

Eliminate all air flow blockages that can force your air conditioner to work overtime. Replace a dirty air filter, open room vents that are shut or covered, and clear away debris that has gathered upon condenser unit fins.

4. Clean Blower Fan

Remove the gunk and grime causing your blower fan to slow down when you follow these steps:

  1. Shut off power to the indoor air handler or furnace.
  2. Remove the panel to access the blower chamber.
  3. Unscrew the circuit board and slide it out of the way.
  4. Loosen the blower motor assembly screws so you can slide it out of the compartment.
  5. Scrub the fan blades with a soft brush to remove grime.
  6. Vacuum away debris on the fan blades and within the blower chamber.
  7. Reattach the blower inside the chamber and replace the circuit board.
  8. Replace the access panel and turn on power to the unit.

For Cincinnati Air Conditioning Repair, Call Thomas & Galbraith

If your air conditioning won’t shut off and you’ve tried the steps above, call us to request repair services for your cooling unit. A professional technician will inspect and diagnose the problem keeping your system running all hours of the day. Our team will fix the malfunction so you can save energy and maintain comfort indoors.

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