Why Is My AC Not Cooling?

Your air conditioner is running, but the air from the vents feels warm or barely cool. It's one of the most common summer calls we get in Gravenhurst and across Muskoka. Some causes take two minutes to fix yourself; others need a technician. Here is how to tell the difference, from a family-owned Muskoka HVAC contractor that has been repairing air conditioning since 1975.

Start With the Simple Checks

Before assuming something is broken, check the basics:

• Thermostat settings. Make sure it is set to cool, the fan is on auto, and the set temperature is below the room temperature. Replace the batteries if the display is dim.
• Breakers and switches. A tripped breaker or a switched-off service disconnect near the outdoor unit means no cooling at all.
• Vents and returns. Closed or blocked supply vents and return grilles restrict airflow through the whole system.
• The condensate drain. Many systems shut down when the drain backs up, as a safety measure.

If those all look right, move on to the causes below.

1. A Dirty Air Filter

A clogged air filter is the number one reason an AC stops cooling well. When airflow drops, the indoor coil can't absorb heat properly, and the system struggles to push cold air through the ducts. Check your filter monthly in summer and replace it when it's visibly grey. See How Often Should You Change Your Furnace Filter? — the same advice applies to the filter your air conditioner shares.

2. A Dirty or Blocked Outdoor Unit

The condenser unit outside releases the heat your home has collected. Grass clippings, cottonwood fluff, leaves and dirt on the coil stop it from doing that. Turn the power off at the disconnect, clear at least a couple of feet of space around the unit, and gently rinse the coil fins with a garden hose from the outside in. Don't use a pressure washer, which bends the fins.

3. A Frozen Evaporator Coil

If you see ice on the refrigerant lines or the indoor coil, the system can't cool. Ice usually comes from restricted airflow or low refrigerant. Turn the AC off, set the fan to run, and let the ice melt completely. If it freezes again after you've replaced the filter, a technician needs to find the underlying cause. Don't chip at the ice.

4. Low Refrigerant or a Leak

Air conditioners don't "use up" refrigerant. If the charge is low, there's a leak somewhere, often at a coil or fitting. Signs include warm air, hissing sounds and ice on the lines. Topping up without finding the leak only delays the problem, so we locate and repair the leak and then restore the correct charge.

5. Failed Electrical Parts

The capacitor, contactor and fan motors in the outdoor unit take a beating from summer heat and storm power surges. A common symptom is a fan that isn't spinning, or a unit that hums but won't start. These are repairs for a trained technician, because capacitors can hold a charge even when the power is off.

6. A Faulty Thermostat or Control Fault

If the thermostat isn't talking to the system, the air handler may run while the outdoor unit never starts. That feels like "the AC is on but not cooling." Smart thermostats can also lose their wiring or settings after a power outage.

7. Leaky or Disconnected Ductwork

Cold air that never reaches the room is cold air wasted. Gaps, disconnected joints and uninsulated ducts in attics, crawl spaces and cottages leak cooled air before it arrives. Uneven cooling between rooms is a clue. See our ductwork installation page if your ducts need replacing.

8. An Old or Undersized System

An air conditioner that is 12 to 15 years old, uses older refrigerant, or was never sized correctly for the house may simply not keep up on the hottest days. If repairs keep adding up, replacement can make more sense. Read When to Replace Your Air Conditioner, or compare options on our air conditioning installation page. A heat pump replaces your AC and heats efficiently too.

When to Call a Technician

Call for AC repair if:

• The filter is clean and the thermostat is set properly, but the air is still warm
• Ice returns after thawing
• The outdoor unit hums, clicks or won't start
• The breaker keeps tripping
• You hear grinding or squealing, or smell burning
• Water is leaking around the indoor unit

Turn the system off if you suspect an electrical or refrigerant problem; running it can damage the compressor, the most important component in the system. Our technicians repair central air conditioners, ductless systems and heat pumps. Learn more about AC repair in Gravenhurst.

Preventing It Next Summer

A spring tune-up lets a technician clean the coils, check the electrical components, clear the drain and test airflow before the first heat wave. Cottage owners in particular should have systems checked after sitting idle all winter. See our cooling services overview.

Frequently Asked Questions

Why is my AC running but blowing warm air? The most common causes are a dirty filter, a dirty outdoor unit, a frozen coil, low refrigerant or a failed outdoor-unit part. Start with the filter and thermostat, then call a technician if the air is still warm.

Why is my central air conditioner not cooling my whole house? Uneven cooling often points to blocked vents, leaky ducts or a system that is too small for the home. A technician can check airflow and the cooling load.

Why is my AC not blowing cold air after I changed the filter? Look at the outdoor unit and breaker next. If the coil is clean and power is on, the problem is likely refrigerant, a frozen coil or an electrical part that needs repair.

Can I add refrigerant myself? No. A low charge means a leak, and refrigerant must be handled by a trained technician.

Should I repair or replace my air conditioner? Age, refrigerant type and the size of the repair all matter. We'll give you an honest recommendation either way.

Get Help With Your AC

Bridlewood Mechanical is a family-owned HVAC contractor based in Gravenhurst, serving Muskoka since 1975. If your air conditioner isn't cooling, we can diagnose it and explain your options.

Book Your Free Quote

Call (705) 706-7622 or request a free quote online.