When your supply vents are blowing room-temperature or warm air while your thermostat is calling for cooling, the cooling circuit has failed while the blower fan continues to push air. Here is how emergency technicians diagnose this issue step by step.
1. Thermostat Fan Mode Misconfiguration
If your thermostat fan switch is set to ON rather than AUTO, the indoor blower fan will run continuously even when the outdoor compressor is cycling off. Switch the fan to AUTO and wait 5 minutes.
2. Tripped Condenser Breaker or Blown Start Capacitor
If the indoor unit is blowing air but the outdoor unit is completely silent, the outdoor breaker may have tripped due to a power surge, or the dual-run capacitor has failed. Without the capacitor, the compressor cannot start, resulting in no heat absorption from your home.
3. Refrigerant Leak (R-410A / R-32)
Air conditioners operate in a closed refrigerant loop. If a pinhole leak develops in the copper copper suction line or aluminum evaporator coils, refrigerant pressure drops. The unit loses thermal transfer capacity, causing vents to blow tepid air.
4. Frozen Evaporator Coil
Check the thick copper suction pipe leading to the outdoor unit. If it is encased in white ice or sweating excessively, air cannot pass through the frozen coil. Turn the AC mode off immediately and run the fan to thaw the system before calling for dispatch.