DIAGNOSTIC_ANALYSIS: AC_SYSTEM_NO_COOLING

Why is my AC not cooling?

A systematic breakdown of the most common reasons air conditioners fail to lower indoor temperatures, from simple airflow issues to complex refrigeration faults.

Primary Causes & Explanations

Clogged Air Filter

45% Prob.

The most common and simplest cause. Restricted airflow prevents the evaporator coil from absorbing heat, often leading to coil icing.

Refrigerant Undercharge (Leaks)

30% Prob.

Low refrigerant levels mean the system cannot move enough heat. Look for oil stains around fittings or freezing on the suction line.

Dirty Condenser Coils

15% Prob.

Mud, grass, or dryer lint on the outdoor unit prevents heat rejection, causing high head pressure and reduced cooling capacity.

Compressor Failure

10% Prob.

The mechanical heart of the system. If the compressor isn't pumping, refrigerant isn't moving. Check for capacitor failure first.

Standard Troubleshooting Protocol

1
Verify thermostat settings and ensure it's in 'Cool' mode with the setpoint below ambient.
2
Inspect the air filter and replace if even slightly restrictive.
3
Check the outdoor unit (condenser) to ensure the fan is running and the coil is clear of debris.
4
Measure the temperature difference (delta-T) between supply and return air (should be 16-22°F).
5
Inspect the evaporator coil and refrigerant lines for signs of frost or icing.

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