AC not cooling

1. Step 01

   Is the outdoor unit running — fan turning, compressor humming?

   YES Go to step 3.

   NO Go to step 2.

2. Step 02

   Is there power at the outdoor disconnect and the breaker?

   YES Contactor, capacitor or compressor. Do not tap the contactor with a screwdriver to test it.

   NO Reset once. A second trip is a fault; leave it off and call.

3. Step 03

   Is the indoor blower running and moving air at the registers?

   YES Go to step 4.

   NO Blower motor, capacitor or control board — or the coil is frozen solid and blocking the air path.

4. Step 04

   Is the filter clean and are all the supply registers open?

   YES Go to step 5.

   NO Replace the filter, open the registers, run the fan for two hours and re-check.

5. Step 05

   Is the temperature split between return and supply air between 16 and 22 °F?

   YES The system is cooling. If the house is still hot, the problem is capacity, distribution or load — not the equipment.

   NO Go to step 6.

6. Step 06

   Is the outdoor coil clean and clear, with 24 inches around it?

   YES Go to step 7.

   NO Rinse it from the inside out with the power off. A blocked condenser cannot reject heat and looks like everything else.

7. Step 07

   Is the indoor coil or the suction line iced?

   YES Turn cooling off, fan on, and let it thaw before anything else.

   NO At this point it is charge, a metering-device fault or a compressor problem — gauges, and a certified technician.

Ice on the indoor coil or the copper suction line has exactly two causes: not enough air over the coil, or not enough refrigerant in it. Both drop the coil temperature below freezing; the condensate then freezes instead of draining, and the ice blocks what airflow was left. It is a runaway.

Thaw it first — cooling off, fan on, four to twenty-four hours. Then decide which cause it was. If the filter was filthy or the static pressure is high, it was airflow. If airflow is fine and it freezes again within a day, it is charge or a restriction, and that needs gauges.

The outdoor fan spins but the compressor does not, or nothing runs at all. Three usual suspects, in order of likelihood: a failed run capacitor, a pitted contactor that will not pull in, or a compressor that has gone to ground.

A capacitor that reads more than about 6% below its rated microfarads is failing even if the unit still starts. It is the least expensive part in the cabinet and the one most likely to be the whole problem.

At step 7, or any time the answer involves refrigerant. Section 608 of the Clean Air Act (40 CFR part 82, subpart F) bans intentional venting of ODS refrigerants and their substitutes, including HFCs, during service, repair or disposal — opening a sealed system without that certification is not a technicality, and a system that has lost charge has a leak that will do it again if nobody finds it.

Before the technician arrives, take the static pressure reading and the temperature split. Handing those over saves the first twenty minutes of the visit and makes it much harder for "it just needs a top-up" to be the diagnosis three summers running.

Sources: US EPA, Stationary Refrigeration and Air Conditioning (read 2026-09-04)