6 Common AC Problems and Quick Fixes

When your AC starts acting up, there are a few things you can do yourself before booking a service call. About half of AC problems come from something simple such as a dirty filter, a clogged drain line, a thermostat setting, or debris around the outdoor unit.

Here are six of the most common AC problems, what to check for yourself, and when to call a professional.

Fix 1: Your AC Is Leaking Water. Start With These Checks.

Water pooling under the indoor unit is one of the most common AC complaints, and the cause is usually a blocked condensate drain line.

Every AC produces condensation as it cools. That water runs into a drip pan under the evaporator coil, then out through a white PVC pipe to an exterior or floor drain. Over time, algae, dust, and debris can build up inside the line, causing water to back up into the pan or overflow onto the floor.

Three quick checks can help narrow down the cause.

• Check the drip pan under the indoor unit for standing water while the AC is running.
• Go outside and confirm water is flowing out at the end of the drain line.
• Look for visible algae at either end of the line

These two steps clear most drain line clogs without a service call.

• Attach a wet/dry shop vac to the outdoor end of the line and run it for 2 to 3 minutes.
• Pour a cup of distilled white vinegar into the cleanout access, which is a small, capped opening on the drain line near the indoor unit.

If leaks continue after clearing, it’s time to call a professional.

Fix 2: Your AC Is Turning On and Off Repeatedly. Here’s Why.

When an AC turns on for a few minutes, shuts off, and keeps repeating that cycle, the system is short cycling, meaning it turns on and off too frequently. It’s hard on the compressor and can drive up your electric bill.

Short cycling has several possible causes.

• A dirty air filter is the most common culprit and the easiest to fix.
• A frozen evaporator coil can also trigger the pattern.
• Low or leaking refrigerant causes the system to cycle off before completing a full run.
• Thermostat issues can send the wrong signal and cause the system to shut off early.
• A system that’s too large for the home, which cools the space too fast, shuts off before completing a full cycle, and repeats that pattern continuously.

Start with what you can check on your own.

• Pull the air filter and replace it if light can’t pass through it
• Look for ice or frost on the indoor coil or outdoor refrigerant line.
• Confirm the thermostat is set to “Cool,” and the temperature is set lower than the current room temperature.

If the filter is clean, no ice is visible, and the thermostat is set correctly, the issue is likely system sizing or refrigerant level. Both require a professional diagnosis.

Fix 3: Your House Is Still Warm. Check the Air Filter.

A dirty air filter is the most common reason a home stays warm despite the AC running. It restricts airflow across the evaporator coil, which prevents the system from cooling effectively.

Before calling a technician check these on your own.

• Pull the filter and hold it up to a bright light. Replace it if the light doesn’t come through.
• Walk outside and check the condenser for debris, tall grass, or shrubs crowding the unit.
• Turn off power at the outdoor disconnect box, which is a small metal box mounted on the wall near the condenser, then rinse the outdoor coil with a garden hose. Never use a pressure washer.

If the filter is fresh and the condenser is clean, the issue is likely low refrigerant or a deeper airflow problem that needs a professional.

Fix 4: Your AC Won’t Turn On. Check the Thermostat and Circuit Breaker.

When the outdoor unit is silent and no air moves through the vents, the AC has stopped receiving power or the right signal from the thermostat.

Five quick checks can rule out the most common causes.

• The thermostat mode should be set to “Cool”
• The temperature setting should be at least 3 to 5 degrees below the current room temperature.
• If the thermostat runs on batteries, swap them out.
• Check the circuit breaker in the electrical panel for a tripped breaker.
• Make sure the outdoor disconnect switch is in the “On” position

If the breaker trips again after you reset it, leave it alone. That points to an electrical fault that needs a licensed technician.

Fix 5: Your AC Is Making Strange Noises. Here’s What They Mean and What to Do.

Every AC makes some noise during normal operation. New or unusual sounds are usually a sign of a specific problem. Here’s what common noises typically point to:

• A grinding sound often points to worn blower motor bearings.
• A screeching noise usually means a fan belt or motor issue.
• Banging or clanking suggests a loose part inside the outdoor unit.
• Hissing can be a sign of a refrigerant leak.
• Clicking often points to a relay, contactor, or capacitor issue.

None of these are DIY fixes. Continuing to run an AC with new mechanical noises usually makes the damage worse.

When you hear something unfamiliar, here’s what to do.

• Shut the system off at the thermostat
• Find the outdoor disconnect box and switch it off
• Note when the sound started and what it sounds like
• Call a licensed technician to diagnose the issue

Fix 6: Your AC Is Running Constantly. When to Call a Pro.

An AC that runs nonstop but never quite reaches the temperature you’ve set is losing capacity. There are a few common reasons this is happening.

• A system that’s too small for the home can’t keep up with the cooling demand.
• Low or leaking refrigerant reduces the system’s ability to cool effectively.
• A dirty or blocked outdoor unit can’t release heat the way it should.
• A failing compressor struggles to maintain consistent cooling.
• Duct leaks allow cool air to escape into unconditioned spaces like the attic or crawl space before it reaches the rooms you’re trying to cool.

The most common causes are easy to rule out on your own.

• See if your air filter needs replacing.
• Rinse the outdoor coil and clear surrounding vegetation
• Confirm the thermostat isn’t set unrealistically low

If the AC runs constantly on a mild day when it’s below 80 degrees outside, the system has a real problem. Continuing to run it wears the compressor faster and drives up your electric bills. Schedule a repair as soon as possible.

Frequently Asked Questions

How do I know if my AC needs a professional?

If the DIY checks don’t fix it, or if you see ice on the refrigerant lines, hear new mechanical noises, or smell burning near the outdoor unit, it’s time for a professional. Continuing to run a struggling AC damages the compressor.

Can I keep running my AC if it’s making noise?

Not if the noise is new. Grinding, screeching, banging, hissing, or clicking sounds usually mean a component is failing. Continuing to run it accelerates the damage.

What’s the difference between short cycling and normal cycling?

Normal cycling is 15 to 20 minutes of runtime followed by a similar off period, several times an hour. Short cycling is under 10 minutes of runtime followed by a quick shutoff, repeating rapidly. Short cycling is a sign of a real problem that needs attention.

How often should I check my AC filter?

At least once a month during the cooling season. Replace it every 1 to 3 months depending on the filter type. Homes with pets or allergies benefit from monthly changes.

Schedule AC Service with Hero

When DIY troubleshooting isn’t working, Hero Home Services is ready to take it from there. We’ve been keeping Twin Cities homes comfortable since 1914. We’re one call or text away from getting your AC back on track.