AC Not Cooling? 7 Things to Check Before Calling a Tech

It’s the middle of a Massachusetts summer, the humidity is climbing, and your air conditioner is running — but your house isn’t getting any cooler. Before you pick up the phone and schedule a service call, there are several things you can check yourself. Many common AC problems have simple solutions that don’t require a technician. Here are 7 things to inspect before calling for help.

1. Check Your Thermostat Settings

It sounds obvious, but thermostat errors are one of the most common “AC not cooling” culprits we see. Start with the basics: make sure the thermostat is set to “COOL” (not “HEAT” or “OFF”), the fan is set to “AUTO” (not “ON” — the “ON” setting runs the fan continuously, which can blow warm air between cooling cycles), and the set temperature is at least 3-5 degrees below the current room temperature.

If you have a programmable or smart thermostat, check that a schedule isn’t overriding your settings. Also verify the batteries — low batteries can cause intermittent operation or inaccurate temperature readings.

2. Inspect and Replace the Air Filter

A dirty air filter is the single most common cause of reduced AC performance. When the filter is clogged, it restricts airflow across the evaporator coil, reducing the system’s ability to absorb heat from your indoor air.

Pull out the filter and hold it up to a light. If you can’t see light through it, it’s time for a replacement. Standard 1-inch filters should be replaced every 30-60 days during cooling season. Thicker 4-inch filters can last 3-6 months. This $10-$25 fix resolves a surprising number of “AC not working” calls.

3. Clear the Outdoor Unit

Your AC’s condenser unit (the big box outside) needs adequate airflow to release heat. Walk outside and check for leaves, grass clippings, mulch, or debris piled against the unit. Overgrown shrubs and plants can also restrict airflow.

Clear at least 2 feet of space around all sides of the outdoor unit. If the fins look dirty or matted, you can gently rinse them with a garden hose (spray from inside out). Never use a pressure washer — it will bend the delicate fins and make the problem worse.

4. Check the Circuit Breaker

Your AC system uses two breakers — one for the indoor air handler or furnace, and one for the outdoor condenser unit. If the outdoor breaker has tripped, the indoor fan will still blow air through your vents, but it won’t be cooled. This can feel like the AC is “running but not cooling.”

Check your electrical panel and reset any tripped breakers. If the breaker trips again immediately or repeatedly, don’t keep resetting it — that indicates an electrical problem that needs professional attention.

5. Make Sure All Vents Are Open and Unblocked

Walk through every room in your home and check that supply and return vents are open and not blocked by furniture, curtains, or rugs. Closing vents in unused rooms is a common practice that actually hurts your system’s performance — it increases pressure in the ductwork and reduces overall efficiency.

While you’re checking vents, feel the air coming out of them. If some rooms have strong airflow and others have weak or no flow, you may have a ductwork problem — a disconnected duct, a damper that’s been closed, or significant leaks.

6. Look for Ice on the Coils

If you see ice forming on the refrigerant lines (the copper pipes running from your outdoor unit to the indoor unit) or on the evaporator coil inside the air handler, that’s a clear sign something is wrong. Ice on the coils blocks airflow and prevents your AC from cooling.

Common causes of frozen coils include a dirty air filter (restricting airflow), low refrigerant levels (from a leak), a malfunctioning blower fan, and dirty evaporator coils. If you see ice, turn the AC off and set the fan to “ON” to let the ice melt. Check and replace your filter. If the coils freeze again after the filter is clean, call a technician.

7. Watch for Signs of Low Refrigerant

Refrigerant is the lifeblood of your AC system. If there’s a leak, your system will gradually lose cooling capacity. Signs of low refrigerant include warm air from the vents even though the system is running, hissing or bubbling sounds near the indoor unit, ice on refrigerant lines or evaporator coil, and higher-than-normal electric bills.

Refrigerant issues always require a professional. It’s illegal to add refrigerant without a proper EPA certification, and simply “topping off” refrigerant without fixing the leak is a temporary and expensive band-aid. A technician will locate and repair the leak, then recharge the system to the correct level.

When It’s Time to Call a Professional

If you’ve gone through all seven checks above and your AC still isn’t cooling properly, it’s time to call a licensed HVAC technician. Other situations that require professional help include unusual noises (grinding, squealing, banging), water leaking from the indoor unit, your AC short cycling (turning on and off rapidly), burning smells when the system runs, and a system that’s over 15 years old and losing performance.

Spencer Home Services offers same-day AC repair on the North Shore. Our technicians arrive with fully stocked trucks and can diagnose most issues in a single visit. Schedule AC repair or call us at (978) 293-5770.

Maintenance Tips to Prevent AC Problems

• Change your filter every 30-60 days during cooling season
• Schedule annual spring maintenance — a pre-season tune-up catches issues before the heat arrives
• Keep the outdoor unit clear — trim vegetation to 2 feet on all sides
• Don’t close vents in unused rooms — it hurts system performance
• Consider a maintenance plan — annual tune-ups extend system life and catch problems early

Should You Repair or Replace Your AC?

If your AC is over 10-12 years old and facing a major repair (compressor, coil replacement, or refrigerant leak), replacement often makes more financial sense. A general rule of thumb: if the repair costs more than 50% of a new system, replacement is usually the better investment.

Modern AC systems are 30-50% more efficient than models from 15 years ago. A new system with a higher SEER2 rating will lower your monthly electric bills, and you may qualify for Mass Save rebates on qualifying high-efficiency installations. Explore AC installation options.

Frequently Asked Questions