Phase 1
Before You Touch the Equipment
Customer Interview and Site Assessment
✓
Ask the customer when the problem started and if anything changed (power outage, thermostat adjustment, filters changed)
Recent changes often point directly to the cause.
✓
Check the thermostat, confirm it is set to COOL, set point is below current room temp, and fan is set to AUTO
Thermostat issues account for more no-cooling calls than most techs expect.
✓
Check all circuit breakers, indoor unit, outdoor unit, and disconnect box at the unit
Check both positions, a tripped breaker may not be fully in the OFF position.
✓
Inspect the air filter, note condition and last change date if known
A severely clogged filter can cause freeze-up and complete loss of cooling.
Phase 2
Indoor Unit Inspection
Air Handler / Furnace
✓
Confirm indoor blower is running, check for airflow at supply registers
✓
Inspect evaporator coil for ice or frost buildup
Frozen coil = restricted airflow or low refrigerant. Do not proceed until ice melts.
✓
Check condensate drain line and drain pan, confirm no blockage or overflow
A full drain pan can trigger a float switch that shuts down the system.
✓
Inspect blower motor capacitor, check microfarad rating against nameplate
✓
Check low voltage wiring at air handler, confirm Y, G, R, C terminals are secure
✓
For light commercial: check economizer operation if equipped, confirm dampers not stuck open
Stuck open economizer brings in hot outside air, killing cooling capacity.
Phase 3
Outdoor Unit Inspection
Condenser Unit
✓
Confirm outdoor unit is running, both compressor and condenser fan motor
✓
Check run capacitor, test microfarad rating on both compressor and fan motor sides
Capacitor failure is one of the most common causes of no cooling in summer heat.
✓
Check contactor, inspect for pitting, burning, or contacts stuck open or welded shut
✓
Measure line voltage at contactor, confirm 208-240V is present
✓
Measure compressor amp draw, compare to nameplate RLA and LRA
✓
Inspect condenser coil, check for blockage, debris, or damage restricting airflow
A blocked condenser coil causes high head pressure and compressor cutout.
✓
Check high and low pressure safety switches, confirm neither is tripped
✓
For light commercial: check phase voltage, confirm no phase imbalance exceeding 2%
Phase 4
Refrigerant System Check
Pressures and Refrigerant Charge
✓
Connect manifold gauges, record suction and discharge pressures
✓
Compare pressures to PT chart for the refrigerant type, note any major deviations
Low suction with low discharge = low charge. High discharge = overcharge or condenser issue.
✓
Measure superheat at suction line, compare to target range for system type
Fixed orifice: 10-18°F. TXV: 8-12°F. High superheat = low charge or restricted metering device.
✓
Measure subcooling at liquid line, compare to target range
Target: 10-15°F. High subcooling = overcharged. Low subcooling = undercharged or restriction.
✓
Inspect refrigerant lines for signs of oil staining or visible leak points
✓
If low charge confirmed, perform leak search before adding refrigerant. Never add without finding the leak.
Phase 5
Verify and Close
Final Verification
✓
After repair, run system through a full cycle and confirm cooling is restored
✓
Record final suction pressure, discharge pressure, superheat, and subcooling readings
✓
Measure supply and return air temperature differential, target 16-22°F delta T
Delta T below 14°F at normal conditions indicates system is not cooling properly.
✓
Document complete CCC entry, Complaint, Cause, Correction with all readings
Before You Leave
Confirm the thermostat is calling for cooling and the system is actively running. Verify outlet air at supply registers is noticeably cooler than return air. Walk the customer through what you found, what you did, and anything to watch for. Never leave a job without verifying the complaint is resolved.