Maintenance, Troubleshooting, and Repair
Diagnose before you add refrigerant
Preventive maintenance prevents most failures: filters, belts and tension, bearings, coil cleaning, condensate drains and traps, electrical connections and contactor pitting, refrigerant charge verification, and combustion analysis with CO testing on fuel-fired equipment. Record baseline readings so future comparisons are meaningful.
Troubleshooting follows a sequence, not intuition. Confirm the complaint, check the simple things (power, thermostat settings, filter, breakers), verify the sequence of operation against the wiring diagram, then measure. On the refrigerant side, low suction pressure with high superheat can be a leak, a restricted metering device, a plugged filter-drier, or low airflow - the surrounding evidence distinguishes them. A frosted suction line, a temperature drop across a drier, or a condenser split that is too small each point somewhere specific.
On electrical calls, verify supply voltage, control transformer output, and continuity of safeties before condemning a motor. Test capacitors by capacitance, not by appearance. Compressor checks include winding resistance balance, insulation to ground, and start components.
Traps: topping off charge to make a gauge read right; replacing a compressor for a failed run capacitor; misdiagnosing a dirty evaporator coil as low charge; ignoring that airflow problems mimic charge problems every time.
Worked example: a system with normal subcooling, low suction pressure, and a 5°F temperature drop across the liquid-line drier points to a restriction, not an undercharge - adding refrigerant would overcharge the system once the restriction is repaired.