Why Is My AC Not Cooling? 7 Common Causes (and What Each Costs to Fix)
Quick answer
When an AC runs but doesn’t cool, the culprit is usually one of seven things: a clogged filter, a tripped breaker, a bad capacitor, low refrigerant from a leak, a frozen evaporator coil, a failing fan motor, or a thermostat problem. Two of those you can check yourself in five minutes. The rest are fast fixes for a technician, and most cost far less than people fear.
Here they are in the order we actually find them on Northern Virginia service calls.
1. A clogged air filter (check this first)
A packed filter chokes airflow, and weak airflow feels exactly like weak cooling. It can even freeze the coil (see #5). Check it yourself: if you can’t see light through the filter, swap it.
Typical cost: the price of a filter. This one call-avoider is why we start every diagnosis at the filter.
2. A tripped breaker or blown disconnect
If the outdoor unit is silent while the indoor fan runs, check your electrical panel for a tripped breaker. Reset it once. If it trips again, stop, a breaker that keeps tripping is protecting you from a real electrical problem, and resetting it repeatedly is how small problems become big ones.
Typical repair cost if there’s an underlying fault: $150 – $600 depending on what’s failing.
3. A failed capacitor
The capacitor is a small part that gives your compressor and fan motors their starting jolt, and it’s the single most common summer failure we see. Classic symptoms: the outdoor unit hums but won’t start, or starts and stops.
Typical cost: $150 – $400 installed. Cheap part, big consequences if you keep running the unit without fixing it.
4. Low refrigerant (which means a leak)
Your AC doesn’t “use up” refrigerant; if it’s low, it leaked. Symptoms: air that’s cool-ish but not cold, ice on the refrigerant lines, and runtimes that never end. A proper fix finds and repairs the leak, then recharges the system to the exact factory charge, not just a top-off that leaks out again by August.
Typical cost: $300 – $1,500+ depending on the leak’s location and refrigerant type. Older R-22 systems cost more to recharge, which often tips the repair-or-replace math.
5. A frozen evaporator coil
If you see ice on the indoor coil or the copper lines, shut the system off and let it thaw (this can take a few hours). Ice is a symptom, not a cause: it means airflow is blocked (usually that filter) or refrigerant is low. Running an iced-up AC can kill the compressor, the most expensive part in the system.
Typical cost: free (thaw + new filter) up to a refrigerant repair if a leak caused it.
6. A failing fan motor
A dead indoor blower means no air at the vents; a dead outdoor fan means the unit can’t shed heat and will overheat and shut down. Grinding, squealing, or a fan that won’t spin are the giveaways.
Typical cost: $300 – $700 installed for most residential fan motors.
7. A thermostat that’s lying to everyone
Sometimes the AC is fine and the brain is the problem: dead batteries, aged sensors, a schedule someone changed, or wiring that’s worked loose. If your thermostat’s display is blank or the temperature reading is obviously wrong, start there.
Typical cost: $0 (batteries) to $150 – $450 for a replacement thermostat, installed.
When to stop troubleshooting and call
Call a professional right away if you notice burning smells, repeated breaker trips, ice on the lines, or a compressor that hums without starting. Each of those can turn a modest repair into a major one if the system keeps running. And if your AC is 12+ years old and this is its second or third failure in as many summers, ask for the honest repair-versus-replace math before putting more money into it.
Frequently asked questions
How fast can someone come out? In peak season, same-day service exists but goes to the people who call early. Morning calls almost always beat afternoon ones.
Should I keep running the AC while I wait? If there’s ice, a burning smell, or a tripping breaker: no, shut it off. Otherwise, running it usually won’t make things worse, just less comfortable.
How do I avoid this next summer? A spring tune-up catches weak capacitors, low refrigerant, and dirty coils before July finds them for you. It’s the cheapest insurance an AC gets.
AC not cooling right now? Leonard Splaine runs same-day AC repair across Northern Virginia with upfront, flat-rate pricing, and the $89 diagnostic is waived for maintenance members. Call 703-494-2855 or request service.
