It is hot outside. Your air conditioner is running — you can hear it, you can feel the air moving — but the house will not cool down. This is one of the most common calls HVAC companies receive every summer, and the good news is that many of the causes are straightforward. Some you can fix yourself in ten minutes. Others need a professional. Here is how to tell the difference.
Before you call anyone and potentially pay an $89 to $150 diagnostic fee, work through this checklist. If the problem is something simple, you will have saved yourself time and money. If it is something that requires professional repair, you will arrive at that call better informed about what might be wrong — which makes you a better customer and reduces the chance of being oversold on an unnecessary repair.
Check These First — Free Fixes That Take Under 10 Minutes
• Check the air filter. A clogged air filter is the single most common cause of an air conditioner running without cooling effectively. When the filter is blocked, airflow through the system is restricted — the system cannot pull enough warm air across the evaporator coil to cool it properly. Pull your filter out and hold it up to a light. If you cannot see light through it, replace it now. A new filter costs $10 to $25 and takes two minutes to install.
• Check the thermostat settings. Make sure the thermostat is set to COOL, not FAN only. FAN mode runs the blower and circulates air without activating the cooling cycle — so you feel airflow but not cold air. Also check that the temperature setpoint is actually below the current room temperature. If the thermostat batteries are low, replace them.
• Check the outdoor unit. Go outside and look at the condenser unit — the large box with a fan on top. Is it running? If the outdoor unit is not running but the indoor unit is, you may have tripped a circuit breaker. Go to your electrical panel and look for a tripped breaker (one that is in the middle position rather than fully on or off). Reset it by turning it fully off, then fully on. If it trips again immediately, stop and call a professional — there is an electrical problem that requires diagnosis.
• Check for ice on the indoor unit. If your system has been running without cooling for several hours, the evaporator coil — the coil inside your indoor air handler — may be iced over. This usually happens because of a dirty filter restricting airflow, or because refrigerant is low. Turn the system off (or to FAN only) for two to four hours to let the ice melt, replace the filter, then turn it back on. If it ices over again, you need a professional — low refrigerant is the likely cause.
• Check the outdoor unit coil for debris. The condenser coil (the fins on the outside of the outdoor unit) can get clogged with grass clippings, leaves, or cottonwood seeds. This blocks the heat rejection that allows the system to cool properly. Turn off the unit at the disconnect switch and gently rinse the coil with a garden hose — not a pressure washer, which can damage the fins. Let it dry, restore power, and try again.
A clogged air filter is the most common cause of an air conditioner running without effectively cooling a home, accounting for a significant portion of HVAC service calls that homeowners could have resolved without professional help. Replacing the filter and checking basic thermostat settings should always be the first step before calling a technician.
When It Needs a Professional
If you have checked the filter, thermostat, breakers, and outdoor unit and the system is still not cooling, you are likely dealing with one of these issues that require a licensed technician:
• Low refrigerant: Your air conditioner uses refrigerant — a chemical that cycles through the system to absorb and reject heat. If the refrigerant level is low due to a leak, the system cannot cool effectively. You cannot add refrigerant yourself — it requires EPA certification to handle, and simply adding more without finding and fixing the leak is a temporary fix at best. A technician will find the leak, repair it, and recharge the system.
• Failed capacitor: Capacitors are components that help the compressor and fan motors start and run. They fail regularly — especially after power surges and in hot climates where outdoor units run hard all summer. A failed capacitor often causes the outdoor unit to run the fan but not the compressor, or not run at all. Capacitor replacement is a common, relatively inexpensive repair ($150 to $400 including labour) when caught early.
• Compressor failure: The compressor is the heart of the cooling system. Compressor failure is the most expensive repair in residential HVAC — parts and labour typically run $1,200 to $2,500 or more. On a system over 10 years old, a failed compressor often makes replacement more economical than repair. This is exactly the repair-versus-replace calculation we covered in a prior article.
• Duct leakage: If your ducts are leaking significantly — losing conditioned air into unconditioned attic or crawlspace — the system may be cooling perfectly but delivering only a fraction of that cooling to your living spaces. A technician can perform a duct leakage test to identify this problem.
What It Might Cost
If professional help is needed, here are the realistic cost ranges in 2026 for the most common cooling problems:
• Diagnostic fee: $89 to $150, usually credited toward the repair if you proceed
• Capacitor replacement: $150 to $400 parts and labour
• Refrigerant recharge (after leak repair): $200 to $600 depending on refrigerant type and quantity
• Leak detection and repair: $200 to $600 depending on location and accessibility
• Contactor replacement: $100 to $300
• Blower motor replacement: $400 to $900
• Evaporator coil replacement: $800 to $2,000
• Compressor replacement: $1,200 to $2,500+
When to Consider Replacement Instead
If your system is 12 to 15 years old and the repair quote is more than $1,000, run this quick calculation: multiply the system's age by the repair cost. If the result exceeds $5,000, replacement is worth seriously considering. A new system will be more efficient, use the new R-454B refrigerant (no more expensive R-22 recharges), and carry a 5 to 10 year parts warranty.
If your system is newer than 10 years and the repair is under $1,000, repair is almost always the better financial choice. Do not let a contractor push you toward replacement on a relatively young system with a modest repair cost.
Frequently Asked Questions
Why is my air conditioner running but not cooling?
The most common causes are a clogged air filter restricting airflow, low refrigerant from a leak, a failed capacitor preventing the compressor from running, or an iced-over evaporator coil. Start by checking and replacing the air filter and verifying thermostat settings before calling a technician.
Can I fix my air conditioner not cooling myself?
Some causes are homeowner-fixable: replace a clogged filter, reset a tripped circuit breaker, clear debris from the outdoor unit, or correct thermostat settings. Low refrigerant, failed capacitors, compressor problems, and duct leakage require a licensed HVAC technician.
How much does it cost to fix an AC that's not cooling?
Costs range from free (filter replacement) to $150 to $400 for a capacitor, $200 to $600 for refrigerant recharge after a leak repair, and $1,200 to $2,500 for compressor replacement. A diagnostic fee of $89 to $150 is typical and usually credited toward the repair.
How long should I wait for my AC to cool the house?
On a very hot day, a properly functioning air conditioner can typically lower indoor temperature by 15 to 20 degrees from outdoor temperature. If your house is 85°F inside when it's 100°F outside and the system is running, give it 30 to 45 minutes to assess progress. If it's been running for an hour without meaningful improvement, the system has a problem.
