A/C Not Cooling? Six Things to Check Before You Call Anyone
A meaningful share of no-cool calls turn out to be one of these six things. Ten minutes could save you a service fee.
Before calling for A/C repair, check the thermostat mode and batteries, the air filter, the breaker panel and outdoor disconnect, the outdoor unit for debris or ice, the condensate drain float switch, and whether any supply registers are closed. These six account for a large share of no-cool calls and most take under ten minutes.
Why this list exists
We would rather tell you how to avoid a service call than collect a diagnostic fee for replacing a filter. It builds the kind of relationship that means you call us when something is actually wrong.
Work through these in order. If you get to the end and the house still is not cooling, you have genuinely useful information to give us on the phone — which often means we bring the right part on the first visit.
One: the thermostat
Set to COOL, not AUTO or OFF. Setpoint below the current room temperature by at least a couple of degrees. Fan on AUTO.
Then check the batteries. A thermostat with weak batteries can display normally and fail to send the signal. If the screen is blank entirely, that is either batteries or the low-voltage fuse on the control board.
Also check that nobody changed the schedule or engaged a hold. In houses with multiple adults and a smart thermostat, this happens more often than anyone admits.
Two: the filter
Pull it out and hold it up to a light. If light does not pass through, that is very likely your problem.
A restricted filter starves airflow across the evaporator coil, the coil drops below freezing, and ice forms. Once iced, the system blows almost nothing. If you find a loaded filter and weak airflow, replace it, switch cooling OFF and the fan to ON, and give it a few hours to thaw before restarting.
Three: the electrical
Check the main panel for a tripped A/C breaker. Then check the outdoor disconnect — a small box on the wall beside the condenser, which contains either a pull-out block or a switch. People turn these off for landscaping or painting and forget.
Reset a tripped breaker once. If it trips again, leave it off and call. A repeatedly tripping breaker means an electrical fault, and resetting it repeatedly is a genuine fire risk rather than a workaround.
Also look for a service switch near the indoor unit — it looks like an ordinary light switch and gets flipped by accident regularly.
Four: the outdoor unit
- Is it running at all? Should be a fan spinning and a compressor hum.
- If it hums but the fan does not spin, that is the classic failed capacitor signature. Call — this is a common, inexpensive repair.
- Is the coil visibly dirty, packed grey rather than clean metal fins?
- Is anything crowding it? Two feet of clearance on all sides.
- Is there ice on the copper lines? That means a refrigerant or airflow problem.
- Any debris in the top grille — palm fronds, plastic bags, landscape rock?
Five: the condensate float switch
If your system shuts off with no obvious reason and the thermostat looks normal, a tripped float switch is a likely cause. It is a small safety device that shuts the system down when water rises in the drain pan or line.
Look at the drain pan under the indoor unit. Standing water means the drain is blocked and the switch did its job. Clearing the drain — a cup of distilled white vinegar in the access tee, or a wet/dry vacuum at the outdoor termination — often restores operation.
That switch is the only thing between a clogged drain and water in your ceiling, so it working is good news even though it feels like a failure.
Six: the registers and returns
Walk the house. Is air coming out of every supply register? Is anything blocking them — furniture, rugs, curtains, boxes? Did someone close vents in unused rooms?
Then check the return grille. A sofa pushed against a return is a surprisingly common cause of "the system is not cooling well," and it is free to fix.
If some registers have strong airflow and others have almost none, that points to a duct problem rather than an equipment problem, which is useful to know before anyone quotes you a new system.
What to tell us if you still need help
Whether the outdoor unit is running and whether the fan spins. Whether air is coming from the vents and whether it is cool, room temperature, or warm. What the thermostat is set to and what the house is actually reading. Any ice, noises, or smells. When the filter was last changed. And whether anyone in the home is heat-vulnerable.
That set of answers lets us triage accurately and frequently means the right part is already on the truck.
Frequently asked
Why is my A/C running but not blowing cold air?
The three usual causes are a failed run capacitor preventing the compressor from starting, low refrigerant from a leak, or restricted airflow from a loaded filter or dirty coil. A frozen evaporator coil produces the same symptom and is almost always downstream of one of those.
Should I reset my A/C breaker?
Once. If it trips again, leave it off and call. A repeatedly tripping breaker indicates an electrical fault — a shorted compressor, a failing motor, or damaged wiring — and repeatedly resetting it is a fire risk, not a fix.
Why did my A/C shut off by itself?
A tripped condensate float switch is a common cause, especially on attic air handlers. It shuts the system down when water backs up in the drain pan, preventing a ceiling leak. Check the pan for standing water and clear the drain line.