Air Conditioner Won't Start — capacitor, compressor

Use only checks that match the exact appliance or system and its official guide.

1. Check 1

   Using only the thermostat's normal user controls, confirm that it has a display, is set to cooling, and is requesting a temperature below the current room temperature; do not remove the thermostat cover or touch its wiring.

   Expected result: Record whether the display is blank, the mode is not cooling, the setpoint is not calling, the display calls for cooling but no equipment responds, or the call starts the indoor blower only.

   Next step: Leave the thermostat wiring untouched and use the matching branch; arrange HVAC service if a valid call produces no response or the display is abnormal.

   Stop if: Do not open the thermostat, bridge terminals, bypass controls, or continue if the thermostat is wet, hot, scorched, or smells burned.

   Why this matters

   Why: A blank or incorrect thermostat state can prevent a start request. A valid cooling call with no response moves attention toward a safety, control, power, capacitor, motor, compressor, or refrigerant issue rather than a setpoint problem.

2. Check 2

   Inspect the accessible air filter according to the equipment instructions, without opening an electrical compartment or reaching into the blower or coil area.

   Expected result: Record whether the filter is clean, visibly gray or blocked, wet, collapsed, incorrectly seated, or unavailable for safe access; note whether airflow at the registers was weak before the shutdown.

   Next step: Use only the exact filter type and installation direction specified for the equipment, then leave the system off and request HVAC service if airflow remains poor, ice is present, or the unit will not start.

   Stop if: Do not force the filter, reach past guards, clean internal coils, or continue if water, ice, smoke, odor, or exposed electrical parts are present.

   Why this matters

   Why: A blocked filter restricts airflow and can contribute to freezing or overheating, but replacing a filter does not diagnose a capacitor or compressor fault. A wet, damaged, or inaccessible filter may indicate another system problem.

3. Check 3

   After one normal thermostat cooling request, observe from a safe distance whether the indoor blower, register airflow, outdoor fan, and compressor area show any response; do not remove a grille, disconnect, or equipment cover.

   Expected result: Record indoor blower only, outdoor fan only, a hum or click without rotation, complete silence, short cycling, or unusual vibration; note whether the house remains warm.

   Next step: Stop repeated calls for cooling and provide the response pattern to an HVAC technician; keep the unit off if there is humming, unusual noise, heat, odor, or a trip.

   Stop if: Do not touch the fan blade, insert tools through the grille, open the disconnect or service panel, test voltage, or try to spin a motor.

   Why this matters

   Why: Indoor-only operation can indicate an outdoor-unit, control, capacitor, contactor, compressor, or safety issue. A hum without start is consistent with a motor-start problem but cannot prove a capacitor. Complete silence can reflect a control or power interruption. These high-voltage components require HVAC diagnosis.

4. Check 4

   From a safe distance, inspect only visible tubing, the indoor access area, and the floor around the air handler for ice, unusual water, scorch marks, or damage; do not touch refrigerant tubing or electrical parts.

   Expected result: Record no visible abnormality, ice on tubing or coil, water near the indoor unit, loud or grinding noise, burning odor, or visible damage; note whether the system was running continuously before stopping.

   Next step: Set the thermostat to a non-cooling state using its ordinary control when ice or abnormal operation is visible, keep the system off, and arrange HVAC service.

   Stop if: Do not chip ice, cut tubing, handle refrigerant, wipe water from electrical parts, or restart the system to force a test.

   Why this matters

   Why: Ice can reflect restricted airflow or low refrigerant and may damage the compressor if the system continues. Water can indicate drainage or thawing concerns. Noise, odor, or scorching increases the need for immediate professional attention.

5. Check 5

   Without approaching electrical equipment, record whether the air conditioner stopped after a breaker, fuse, safety device, or control indication changed; do not operate the breaker, disconnect, or fuse as a test.

   Expected result: Record the time of the stop, whether the indoor and outdoor sections changed together, whether a protection device visibly tripped from a safe existing view, and whether the event repeats without another attempt.

   Next step: Leave the unit off and give the sequence to an HVAC technician or electrician; do not restore power from an electrical enclosure.

   Stop if: Do not reset repeatedly, hold a device on, replace a fuse, open a panel, or continue after smoke, odor, heat, arcing, or water.

   Why this matters

   Why: A protection event can follow overload, short circuit, water backup, motor, capacitor, compressor, or other faults. A device that trips again is not evidence that it merely needs another reset and requires professional diagnosis.

6. Check 6

   Prepare a service handoff describing thermostat state, filter condition, indoor and outdoor response, sound, ice or water, and any protection event; do not open the outdoor unit to photograph or identify the capacitor or compressor.

   Expected result: Record the model information only if already printed on an exterior label, the last time the system ran normally, and whether the symptom is complete silence, humming, short cycling, or a failed compressor start.

   Next step: Keep the system off when an abnormal symptom is present and arrange licensed HVAC diagnosis; provide the record and exterior model information to the technician.

   Stop if: Do not touch or discharge a capacitor, test capacitance or voltage, handle refrigerant, remove covers, or keep restarting the unit.

   Why this matters

   Why: These observations help an HVAC professional distinguish a control request, airflow condition, capacitor or motor symptom, compressor issue, refrigerant safety shutdown, or electrical fault without exposing the homeowner to stored charge or high voltage.