Frequently Encountered Spring A/C Problems

Most air conditioning failures during a southern New Hampshire summer are not surprises. They are predictable, recurring issues that surface every spring when the system runs for the first time in eight months. A handful of them account for the majority of no-cool service calls.

Below are the ten problems we see most often, what causes them, and what a homeowner can do about each one. Knowing these in advance often turns a $200 emergency call into a $4 filter swap or a 30-second breaker reset.

1. Tripped breaker

One of the most common no-cool causes. The system tries to start on the first warm day, draws inrush current, and a marginal breaker trips.

Reset the breaker once. Flip it fully Off, then back On.
If it trips again immediately, leave it off and call for service. Repeated tripping usually indicates a real electrical issue (bad capacitor, loose connection, failed contactor).

2. Dirty air filter

A clogged filter restricts airflow across the indoor coil, which lowers coil temperature, eventually ices the coil, and shuts the system down or causes water damage.

Check 1-inch filters monthly. Replace at least every three months.
4 to 5-inch media filters last six to twelve months.
If you have pets or run the fan continuously, change more often.

3. Refrigerant leaks

An air conditioning system is a sealed loop. It should never leak refrigerant. When it does, capacity drops, electricity use rises, the indoor coil may freeze, and the compressor can be damaged. Refrigerants are also greenhouse gases.

Common leak points include the Schrader valve cores, connections at the line set, and the indoor coil itself. Diagnosis requires electronic leak detection, dye injection, or pressure decay testing. Topping off a leaking system without finding and fixing the leak is a short-term fix at best.

4. System disconnect switch turned off

Most furnaces, air handlers, and outdoor condensers have a service disconnect switch nearby. The indoor one looks like a regular wall switch and is sometimes flipped off by accident.

Check the wall switch near the indoor unit.
Check the disconnect box on the wall next to the outdoor unit.
Both must be On for the system to operate.

5. Thermostat problems

Confirm the thermostat is set to Cool (not Off, Heat, or Auto in cool weather).
Confirm the setpoint is below the current room temperature.
Battery-powered thermostats need fresh batteries annually. A blank or dim screen is the giveaway.
Smart thermostats configured incorrectly for the equipment (especially heat pumps with backup heat) can cause comfort or efficiency issues that look like an equipment problem.

6. Clogged condensate drain

Air conditioners pull moisture out of humid NH summer air. That moisture drains through a small condensate line, typically into a plumbing drain or a condensate pump. Algae and slime build up in the line over time and can clog it, which triggers a safety switch and shuts the system down (or worse, causes water damage if there is no safety switch).

The condensate line is cleared as part of an annual AC tune-up.
Some homeowners pour a cup of distilled vinegar into the access port a few times per cooling season.

7. Failed contactor

The contactor is the electromechanical switch in the outdoor unit that connects the compressor to power when the thermostat calls for cooling. Symptoms of a failing contactor:

Stuck closed: the outdoor unit runs continuously, even when the thermostat is satisfied.
Stuck open: the outdoor unit will not start at all.
Pitted contacts: intermittent operation, sometimes accompanied by a humming or chattering sound.

Contactors are inexpensive parts that wear out over time. They are checked and replaced as needed during annual service.

8. Dirty evaporator coil

The evaporator coil is the indoor coil that the blower pushes air through. Over years of operation, dust and debris coat the coil fins and reduce heat transfer and airflow. A dirty evaporator coil increases operating cost and reduces cooling capacity.

A coil with light dust can be cleaned in place.
A heavily fouled coil sometimes requires pull-and-clean service.
Keeping the air filter changed on schedule is the single best way to keep the evaporator coil clean.

9. Dirty condenser coil

The outdoor coil rejects heat from your home to the outside air. When it is coated with pollen, cottonwood fluff, grass clippings, or pet hair, the unit has to work harder and longer for the same cooling.

Rinse the outdoor coil gently with a garden hose from the inside out (after disconnecting power at the disconnect box).
Avoid pressure washers. They can bend fins and damage the coil.
Keep shrubs and tall grass at least two feet back from the unit.

10. Duct leaks

If the ducts that deliver cool air to living spaces leak (and the ducts run through a hot attic or a damp basement), you are paying to cool unconditioned space. Duct leakage is one of the leading causes of inefficient AC operation and uneven comfort in NH homes.

Seal accessible ductwork with foil tape (UL 181) or mastic, not standard cloth duct tape.
For a complete fix, a contractor with duct-blaster equipment can quantify and seal leaks throughout the system.

Avoid the surprise: schedule a spring tune-up

Most of the problems above are caught and addressed during an annual spring AC tune-up, well before the first 90°F day. Our schedule fills fastest after the first heat wave.

To schedule an AC tune-up in southern New Hampshire, contact A.J. LeBlanc Heating. Serving NH families since 1928.

Frequently Asked Questions

When is the best time to schedule AC maintenance?

Late March through May, before the first hot day. Demand is lighter and scheduling is easier.

How often should I change my AC filter?

Check 1-inch filters monthly and replace at least every three months; 4 to 5-inch media filters last six to twelve months. Pets or active renovation projects push you to the shorter end.

My AC is blowing cool air but not cold. What is wrong?

The most common causes are low refrigerant, a dirty evaporator coil, a clogged filter restricting airflow, or a failing compressor. The first three are routine maintenance issues. The fourth is a major repair.

Why is water dripping from my indoor unit?

Almost always a clogged condensate drain. The drain pan overflows when it cannot drain to the plumbing line. Clear the drain and inspect for algae buildup.

Should I cover my outdoor AC unit in winter?

Not fully. A solid cover traps moisture and invites rodents. A breathable mesh cover on the top only is the most that is typically recommended. Most outdoor condensers are engineered to handle weather year-round.