HVAC Troubleshooting Guide
Systematic diagnostic procedures for common HVAC problems — for professional technicians.
Common Problems & Solutions
System Not Cooling
Check first:
- Thermostat settings and batteries
- Air filter — replace if dirty
- Circuit breakers — reset if tripped
- Outdoor unit — clear debris, check contactor
If still not cooling: Check refrigerant charge (superheat/subcooling), compressor operation, TXV function
System Not Heating
Check first:
- Thermostat set to HEAT mode
- Gas supply (furnaces) — pilot light, gas valve
- Heat pump — reversing valve operation
- Igniter and flame sensor (furnaces)
If still not heating: Check control board error codes, heat exchanger for cracks, heat pump refrigerant charge
Short Cycling
Common causes:
- Oversized equipment for the space
- Refrigerant overcharge or undercharge
- Dirty evaporator or condenser coil
- Low airflow — dirty filter, blocked registers
- Faulty thermostat or control board
Unusual Noises
Diagnose by sound:
- Banging: Loose parts, failing compressor
- Squealing: Belt or bearing issue
- Clicking: Relay/contactor issue
- Hissing: Refrigerant leak
- Rattling: Loose panels or debris
Water Leaks / Condensate Issues
Common causes:
- Clogged condensate drain line
- Dirty evaporator coil causing freeze/thaw
- Cracked or overflowing drain pan
- Condensate pump failure
- Refrigerant undercharge causing freeze-up
High Energy Bills
Common causes:
- Dirty air filter reducing airflow
- Refrigerant charge off (over or under)
- Dirty coils reducing heat transfer
- Duct leaks losing conditioned air
- Failing capacitor reducing motor efficiency
Diagnostic Resources
PM Checklists
Preventive maintenance checklists for all system types Refrigerant Guide
Refrigerant types, properties, and handling HVAC Glossary
Technical terms and definitions Parts Identification
Identify HVAC components by name and function
Preventive maintenance checklists for all system types Refrigerant Guide
Refrigerant types, properties, and handling HVAC Glossary
Technical terms and definitions Parts Identification
Identify HVAC components by name and function
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