HVAC Technician how-to
How to Diagnose an AC That Isn’t Cooling
A systematic approach finds the cause faster and avoids unnecessary parts. Follow electrical safety and EPA rules.
A systematic approach finds the cause faster and avoids unnecessary parts. Follow electrical safety and EPA rules. In short: talk; check; inspect, then complete the remaining steps below.
Step by step
Talk to the customer: when did it start, any noises, is anything running?
Check the thermostat settings, batteries and that it is calling for cooling.
Inspect the air filter and indoor airflow: a clogged filter or frozen coil is common.
At the outdoor unit, verify power, check the disconnect and look for a running fan and compressor.
With power off and capacitors discharged, test the capacitor, contactor and wiring.
If electrical components are good, connect gauges and check pressures, superheat and subcooling.
Explain findings and options to the customer before repairing.
Safety reminders for HVAC technicians
- Disconnect power and lock out before servicing electrical components
- Wear gloves and eye protection when handling refrigerants: they can cause frostbite
- Never vent refrigerants; recover them as required by EPA rules
- Use fall protection on roofs and follow ladder safety
Key terms
BTU · Ton (cooling) · SEER2 · Refrigeration cycle · Compressor · Condenser: see the full HVAC technician glossary.