Step 3: Electrical System Testing and Component Diagnosis

Goal: Test electrical components including capacitors, contactors, and wiring using professional diagnostic techniques

1. Locate and safely discharge the capacitor:

   • Find the capacitor in the outdoor unit (cylindrical component with wires)
   • Use a capacitor discharge tool or insulated screwdriver to safely discharge stored energy
   • Touch the discharge tool across both capacitor terminals simultaneously for 5 seconds
   • Expected result: Any stored electrical charge is safely dissipated

2. Test capacitor with multimeter:

   • Set your multimeter to capacitance mode (usually marked as µF or nF)
   • Touch multimeter probes to the capacitor terminals
   • Compare reading to the rated value printed on capacitor label (e.g., 45µF)
   • Expected result: Reading should be within 10% of rated value (40.5-49.5µF for a 45µF capacitor)

3. Inspect capacitor for physical damage:

   • Look for bulging, leaking, or burnt appearance
   • Check for corroded terminals or loose wire connections
   • Smell for any burning odor or chemical smell
   • Expected result: Physical condition assessment reveals any obvious failure signs

4. Test contactor switch operation:

   • Locate the contactor (square relay with thick wires and thin control wires)
   • Use multimeter on resistance mode (Ω) to test coil resistance
   • Test between the two thin coil terminals - should read 10-100 ohms
   • Expected result: Coil resistance within normal range indicates functional electromagnet

5. Test contactor contact points:

   • Set multimeter to continuity mode (usually has a sound symbol)
   • Test across the main contact points (thick wires) when contactor is not energized
   • Should show open circuit (no continuity) when contactor is off
   • Expected result: Contacts are properly open when system is not running

6. Test high voltage wiring connections:

   • Use non-contact voltage tester to verify power is still OFF
   • Inspect all wire connections for tightness and corrosion
   • Check wire insulation for cracks, burns, or animal damage
   • Expected result: All connections secure with no visible damage to wiring

If capacitor reads 0µF or infinite: Capacitor is failed and needs replacement
If contactor coil shows infinite resistance: Coil is burned out - replace entire contactor
If contact points show continuity when off: Contacts are welded - replace contactor immediately

You'll know you're done when: All electrical components are tested and their condition is determined

• Capacitor tested and reading compared to rated value
• Contactor coil resistance measured and within normal range
• Contact points tested for proper operation
• All electrical connections inspected and secured
• Any failed components identified for replacement

Ready for next step? You've diagnosed the electrical system and can now check the mechanical components that affect airflow and cooling.