AC Not Cooling but the Fan Is Running? What It Means in Tempe (2026)

"The fan's running but it's not cooling" is the most common sentence we hear on the phone in Tempe from June through September. It's also the most useful one, because which fan is running narrows the problem to two or three parts before we leave the shop.

Here's how to read it. Two of these you can check yourself in five minutes. The rest, shut the system off and call.

First: which fan?

There are two. The indoor blower pushes air through your vents. The outdoor fan sits on top of the condenser (or inside the rooftop unit) and dumps heat outside. Walk out to the unit and look.

• Air at the vents, outdoor fan spinning, no cold: compressor isn't running, or the system is low on refrigerant, or the coil is frozen. Sections 1 through 3.
• Air at the vents, outdoor unit silent or humming: capacitor, contactor, or a tripped breaker. Sections 4 and 5.
• Air at the vents, warm, outdoor unit cycling on and off every couple of minutes: usually a dirty filter or dirty outdoor coil. Section 6.

If the thermostat fan setting is on ON instead of AUTO, the blower runs all the time, including when the system isn't calling for cooling. Switch it to AUTO. That alone is about one in fifteen "not cooling" calls, and it's free.

1. Compressor won't start (outdoor fan runs, no cold)

The outdoor fan and the compressor share a capacitor but are separate loads. When the fan spins and the compressor doesn't, you'll usually hear a hum or a click every few minutes as it tries. The usual causes, in order: a weak run capacitor, a failed compressor contactor, or the compressor itself.

Cost: capacitor $165 to $245 installed, our price. Contactor $150 to $350. A dead compressor is $1,500 to $3,000+, and on a unit past 12 years that's the repair-or-replace conversation.

Don't: keep running it. A compressor trying to start against a bad capacitor overheats, and that's how a $200 repair becomes a $2,500 one.

2. Low refrigerant (everything runs, air is barely cool)

Both fans run, the compressor runs, and the air at the vents is cool-ish but never cold. Over a few days the house creeps up two or three degrees past the setpoint and never comes back. Refrigerant doesn't get used up; low means a leak.

Cost: finding and repairing the leak plus a recharge, $500 to $1,500+. If your system is pre-2010 and runs R-22, the refrigerant alone can make the repair not worth doing. Full numbers in our Tempe repair cost guide.

Don't: pay for a "top-off" with no leak search. It's the same bill again next July.

3. Frozen evaporator coil (fan runs, weak airflow, then nothing)

Airflow drops to a trickle, the air that does come out is cold, and if you look at the indoor unit or the copper line at the condenser there's frost. The coil iced over, usually from a clogged filter or low refrigerant, and now air can't pass through it.

Fix it yourself, step one: turn the thermostat to OFF and the fan to ON. Let it thaw for two to four hours. Change the filter. If it runs normally after that, you're done and it was the filter. If it freezes again inside a week, it's refrigerant. Call.

4. Capacitor (outdoor unit hums, fan won't spin)

The outdoor fan isn't turning, or it twitches and stops, and the unit hums. This is the number one AC failure in Arizona and the one most likely to hit on the hottest day of the year, because heat is what kills them. Sometimes you can start the fan by pushing the blade with a stick. If that works, it's the capacitor, and it'll fail for good within days.

Cost: $165 to $245 installed, our price. The market range is $150 to $400, and we've seen $700 invoices for the same twenty-minute job. Here's why.

5. Breaker or disconnect (outdoor unit dead silent)

Nothing at the outdoor unit, not even a hum, but the indoor blower runs. Check the breaker panel for a tripped double breaker labeled AC or condenser, and the gray disconnect box on the wall next to the unit. Reset once. If it trips again, stop. Something is pulling too much current, usually a failing compressor or a shorted motor, and resetting it a third time is how you finish the job of burning it out.

6. Short cycling (runs two minutes, stops, repeats)

The unit kicks on, runs briefly, shuts off, and does it again a few minutes later. The house never catches up. In Tempe the usual cause is a condenser coil packed with dust and cottonwood fluff, or a filter so loaded the system overheats and trips its own safety. Hose the outdoor coil gently from the inside out, change the filter, and see if it settles down. If it doesn't, it can be a refrigerant problem or an oversized system, and that's a diagnosis call.

Before you call anyone

1. Thermostat on COOL, fan on AUTO, setpoint below room temperature.
2. Filter. If you can't remember changing it, change it.
3. Breaker and disconnect, one reset only.
4. Walk outside. Is the fan spinning? Is the unit humming, silent, or cycling? Tell us that on the phone and we'll usually know what's on the truck before we leave.