Why Is My AC Not Cooling But Fan Is Running?

1. 1. Outdoor breaker tripped or disconnect pulled

   The most common reason for a live blower and a dead condenser. Service work, a storm, or a nuisance trip can leave the outdoor unit unpowered.

2. 2. Failed run capacitor

   Capacitors are the highest-frequency failure in residential AC. Without one, the compressor and fan cannot start — you may hear a hum.

3. 3. Burnt or stuck contactor

   The contactor is the relay that switches high voltage to the condenser. Pitted contacts stop the outdoor unit from energizing.

4. 4. Low-pressure lockout from refrigerant loss

   Safety switches shut the compressor down when charge is too low, while the indoor blower keeps running normally.

5. 5. Compressor failure

   A shorted, open or seized compressor stops cooling entirely. The fan may or may not still spin depending on the failure.

6. 6. Control board or thermostat wiring fault

   A broken Y-wire delivers a fan call without a compressor call — the blower runs and nothing else does.

• Go outside and confirm whether the condenser is running at all.
• Check the outdoor disconnect box near the unit — the pull-out should be fully seated.
• Check the AC breaker in the panel; reset it once only if tripped.
• Listen for a hum or click at the outdoor unit when the thermostat calls.
• Confirm the thermostat is on COOL with the fan on AUTO.
• Look for ice on the refrigerant lines, which can indicate a charge problem.

Each test isolates one specific cause so you know what you are dealing with before anyone quotes you a repair. Stop immediately if anything feels unsafe.

• Disconnect and breaker check

  About 5 minutesTools: None

  Tests for: Outdoor breaker tripped or disconnect pulled

  1. Locate the outdoor disconnect box mounted near the condenser.
  2. Confirm the pull-out block is fully seated in the slot.
  3. Go to the electrical panel and find the AC breaker.
  4. Reset it once if it is tripped, then wait five minutes.

  Normal result

  The condenser starts within a minute of resetting power.

  Problem result

  The breaker trips again immediately or the unit stays silent.

  What it means: A single clean reset points to a nuisance trip; an immediate repeat trip means a real electrical fault needs a technician.

• Listen for a stalled hum

  About 3 minutesTools: None

  Tests for: Failed run capacitor

  1. Set the thermostat to call for cooling and go outside.
  2. Stand a safe distance from the condenser cabinet.
  3. Listen for a steady hum with no fan blade movement.
  4. Turn the thermostat off if you hear this and do not attempt a restart.

  Normal result

  The fan blade spins and the unit runs smoothly.

  Problem result

  A hum continues with the fan not turning.

  What it means: A humming, non-starting compressor or fan usually means a weak or failed capacitor and needs a technician.

• Check for ice on the lines

  About 5 minutesTools: Flashlight

  Tests for: Low-pressure lockout from refrigerant loss

  1. Locate the two copper lines running from the indoor unit to outside.
  2. Inspect the larger, insulated suction line for ice or frost.
  3. Check the smaller liquid line as well.
  4. Note whether the blower keeps running while the outdoor unit is silent.

  Normal result

  Both lines are clean, cool, and free of ice.

  Problem result

  Ice coats the suction line or fittings.

  What it means: Ice combined with a dead outdoor unit suggests a low-refrigerant safety lockout, which requires professional leak repair.

• Confirm the thermostat call mode

  About 3 minutesTools: None

  Tests for: Control board or thermostat wiring fault

  1. Check that the thermostat is set to COOL, not FAN or OFF.
  2. Set the fan switch to AUTO rather than ON.
  3. Lower the setpoint several degrees below room temperature.
  4. Wait two minutes and check the outdoor unit again.

  Normal result

  The outdoor unit starts within a couple of minutes of the new setpoint.

  Problem result

  The blower keeps running but the outdoor unit never starts.

  What it means: This pattern isolates the fault to the compressor circuit or the wiring that calls for it, separate from thermostat settings.

• Reset tripped breaker

  DIY

  $0

  Professional

  Not needed if it holds

  Typical time

  5 minutes

• Run capacitor replacement

  DIY

  Not a DIY repair

  Professional

  $150-$350

  Typical time

  30-60 minutes

• Contactor replacement

  DIY

  Not a DIY repair

  Professional

  $150-$300

  Typical time

  30-60 minutes

• Refrigerant leak search and recharge

  DIY

  Not a DIY repair

  Professional

  $300-$1,500+

  Typical time

  1-4 hours

• Compressor replacement

  DIY

  Not a DIY repair

  Professional

  $1,500-$3,500+

  Typical time

  3-6 hours

Ranges are national estimates for planning only. Local labor rates, equipment access and parts availability change what you will actually be quoted.

1. Is the outdoor unit completely silent during a cooling call?

   Yes: Check breaker and disconnect first; if both are fine, this is an electrical repair.

   No: Continue.

2. Does the outdoor unit hum without the fan turning?

   Yes: Classic failed capacitor or seized motor. Shut it off and call a technician.

   No: Continue.

3. Does the compressor start and then stop within seconds or minutes?

   Yes: Suspect an overload, a lockout, or a pressure-switch trip.

   No: If it runs steadily but there is no cooling, have charge and compressor performance measured.

What the technician will check

• Verifies 24V control signal reaching the contactor.
• Tests the run capacitor and contactor.
• Measures compressor windings and amp draw.
• Checks pressure switches and refrigerant charge.
• Confirms line-voltage supply at the disconnect.

Repair considerations

• • Capacitor and contactor repairs are among the least expensive AC repairs.
• • A locked-out system due to refrigerant loss requires leak repair before it will hold a charge.
• • Compressor replacement cost depends heavily on warranty status and system age.

What this actually means

In a split system the air handler and the condensing unit have separate power feeds and separate failure modes. A working blower proves the thermostat is calling, the control transformer is alive, and indoor power is fine. That leaves the outdoor half — which is where the cooling actually happens.

• The outdoor unit will not run and the breaker is on.
• The unit hums, buzzes or clicks without starting.
• The compressor starts and stops repeatedly.
• The breaker trips more than once.

• • Have capacitors and contactors tested during annual service — they degrade predictably.
• • Keep the outdoor unit clear so it does not run hot and stress electrical parts.
• • Address slow cooling decline early to avoid a low-charge lockout mid-summer.

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