Why Is My AC Running but Not Cooling? 7 Common Causes

Imagine this: your air conditioner is running, air is coming through the vents and yet -- your home still feels warm! It's one of the most frustrating cooling problems to experience, especially in the height of Michigan summer.

When an AC is running but not cooling, the cause may be as simple as an incorrect thermostat setting or a dirty filter. It can also point to a frozen coil, refrigerant leak, electrical problem or failed component that requires professional service.

Before you assume the worst, here are seven common causes, a few safe checks you can make yourself and some clear signs that it's time to call for an HVAC technician.

1. Your thermostat is on the wrong setting

If your home cooling isn't what you're expecting, start with the simplest possibility: the thermostat.

Confirm that it is set to COOL and that the target temperature is below the current room temperature. If the fan is set to ON, the blower will continue circulating air even when the AC is not actively cooling. That can make it seem as though warm air is coming from the AC vents between cooling cycles. Set the fan to AUTO so it will run with the cooling cycle.

If you have a programmable thermostat or a smart thermostat, review its schedule, vacation mode or energy-saving settings. A recent power interruption or an accidental change can affect its programming.

Safe homeowner check: Review the thermostat mode, temperature and fan settings. Replace its batteries if the display seems dim, blank and your model uses replaceable batteries.

2. A Dirty filter or restricted airflow is limiting cooling

Your air conditioner needs steady airflow to absorb heat from your home. A clogged filter makes it harder for air to pass through your system, which can reduce cooling, create weak airflow and contribute to a frozen evaporator coil.

Blocked supply vents and return grilles can cause similar problems. Furniture, rugs, curtains or household items may restrict the air your system needs to work properly.

Safe homeowner check: Look at the filter. Replace if it's visibly dirty. Ensure you are using the correct size and type for your system. Make sure your supply vents and return grilles are open and unobstructed. Do not reach into the ductwork yourself or remove equipment panels.

3. The Outdoor unit is blocked or malfunctioning

The outdoor unit releases the heat your AC removes from inside the house into the air outside. Grass clippings, leaves, weeds and other debris around/inside the unit can restrict airflow and make heat transfer less effective. If the indoor fan is blowing but the outdoor equipment is not running, the air coming from your vents may not feel cool.

Safe homeowner check: From the outside, look for obvious vegetation or loose debris blocking the space around the unit. Keep the surrounding area clear, but do not remove the cabinet, reach inside, bend the fins or use a pressure washer. If the outdoor unit is silent, repeatedly starts or stops or makes an unusual buzzing or grinding sound, schedule service. Do not attempt to fix the system yourself.

4. The Evaporator Coil is Frozen

Ice on an air conditioner does not mean it's cooling well. A frozen evaporator coil cannot absorb heat properly, so you may notice weak airflow, warmer indoor temperatures or ice on a visible refrigerant line near the indoor equipment.

A coil may freeze for many reasons: because of restricted airflow, a dirty filter, a blower problem or low/leaking refrigerant. Simply thawing it does not correct the underlying issue and running the AC unit while it's frozen can lead to more damage.

Safe homeowner check: If you can see ice, turn the system off. Do not chip or scrape the ice, use a hair dryer, heat gun or remove the access panel. Call a technician.

5. A condensate drain problem has interrupted cooling

As your AC cools the air, it also removes moisture. That moisture normally drains away through a condensate line. If the drain line becomes clogged, a safety switch may interrupt part or all of the cooling operation to help prevent water damage. Depending on the system, the blower may still move air even though the home is no longer being cooled.

Watch for water near the indoor equipment, a full drain pain or repeated system shutdowns. Because water and electrical components are a dangerous combination, avoid opening the unit or attempting an internal repair.

Safe homeowner check: Look for visible water around the equipment from a safe distance. If you see leaking or pooled water, immediately turn off the system at the thermostat and contact a professional. Do not attempt the repair yourself.

6. The System Has a Refrigerant Problem

Refrigerant absorbs heat from your indoor air. If the system has too little refrigerant because of a leak, it may run for long periods of time without cooling the house effectively. Other possible clues include ice on a refrigerant line, hissing or bubbling sounds, or gradually declining cooling performance.

An air conditioner does not normally 'use up' refrigerant. A technician needs to locate the cause, make the appropriate repair and handle the refrigerant according to applicable requirements. Adding refrigerant without addressing the main issue is not a lasting solution.

Safe homeowner check: Refrigerant work requires specialized training and tools. Please do not disconnect a line, open equipment or attempt to recharge your HVAC system yourself.

7. An Electrical or Mechanical component has failed

Your AC depends on several parts working together in tandem, including motors, controls, sensors, capacitors, contactors and the compressor. If any of these components fail, you may hear the indoor fan while the system produces little-to-no cooling.

Electrical failures are not safe DIY (do-it-yourself) repairs. AC components carry dangerous voltage and capacitors may retain a charge even when the equipment is turned off.

Safe homeowner check: An electrical or mechanical component failure is a technician-only repair. Do not remove the access panel, touch wiring or repeatedly reset a tripped breaker. If you notice burning odors, buzzing, smoke, sparking or a breaker that trips more than once, turn the system off and request professional service promptly.

What can I safely do as a homeowner before calling a repair tech?

Homeowners can safely perform a short visual check without opening or taking apart any equipment:

1. Confirm your thermostat is set to COOL, the temperature is set below the current room reading and the fan is on AUTO.

2. Check whether the air filter is visibly dirty and replace with your furnace's corresponding filter if needed.

3. Make sure indoor supply vents and return grilles are open and unobstructed by furniture, debris, etc.

4. Look for leaves, weeds or other debris blocking airflow and the outdoor unit.

5. Look for visible ice, leaking water, unusual sounds, burning odors or an outdoor unit that is not operating.

If you have attempted all of these steps and your AC still isn't cooling, stop there. Opening the cabinet or attempting electrical, refrigerant or internal component repairs can create a serious safety risk and may cause additional damage.

when should i call an hvac technician?

If the thermostat, filter, vents and outdoor clearance all seem normal but your house is not cooling, the system needs a professional diagnosis. You should also call if your system is experiencing any of the following:

• Warm air is blowing from the vents

• Airflow is weak or nonexistent

• You see ice or water accumulating near the equipment

• The outdoor unit is not running or is making unusual noises

• The AC runs constantly without reaching the set temperature

• Your breaker trips more than once

• You smell burning, see smoke or sparking

Before the appointment, note when the problem began, whether it affects the entire house or only some rooms, and any sounds, odors, ice or water you've observed. These details can help the technician troubleshoot more efficiently.

Get your cool air back with 365 mechanical

When the summer heat settles over Dexter and the surrounding areas, you should be able to count on your air conditioner. 365 Mechanical services all makes, models and provides experienced HVAC repair throughout Washtenaw County. Explore our Residential HVAC Services page to learn more.

Humidity can also make a properly-cooled home feel warmer and stickier than expected. If the temperature feels comfortable, but you're still damp -- read about The Benefits of a Whole-Home Dehumidifier in the Summer.

Still feeling warm air? Schedule A/C repair with 365 Mechanical today -- call 734-726-5558.