Here is a guide to checking and changing a contractor

How to Check an HVAC Contactor

Tools Needed

• Screwdriver (usually Phillips)

• Multimeter

• Needle-nose pliers (optional)

• Insulated gloves (recommended)

1. Turn Off Power

Always shut off:

• The outdoor disconnect

• The breaker inside the panel

This prevents shock and protects the equipment.

2. Open the Condenser Panel

Remove the screws on the side panel of the outdoor AC unit to access the electrical compartment.

3. Locate the Contactor

A contactor:

• Is rectangular

• Has a big center plunger/coil

• Has wires on both sides (line voltage in, load voltage out)

• Often has 2 metal contacts that pull in when the thermostat calls for cooling.

4. Visual Inspection

Look for:

• Burnt or pitted contacts

• Melted plastic

• Buzzing coil (when running)

• Contacts stuck closed or open

If contacts are heavily pitted or stuck → replace it.

5. Check with a Multimeter

A. Check the Coil (Low Voltage Side)

Set multimeter to AC volts.

• Touch leads to the 24v coil terminals.

• Have someone turn thermostat to COOL.

You should get 24V.

• If you DO have 24V and the plunger doesn’t pull in → bad contactor.

• If you DO NOT have 24V → problem is upstream (thermostat, board, float switch, etc.).

B. Check Continuity (Power Off)

Set multimeter to continuity/ohms.

• With the contactor pressed IN (manually), check across the top and bottom lugs.

If it does not show continuity → contacts are bad.

How to Replace an HVAC Contactor

1. Turn Off Power Again

Confirm no power with your meter.

2. Take a Photo of the Wiring

This saves you if you forget where wires go.

3. Remove the Wires

• Pull off the low voltage coil wires (usually blue/yellow or brown).

• Remove line and load wires (may require screwdriver or pulling spade terminals).

4. Remove the Contactor

Usually held in by 2 screws.

5. Install the New Contactor

• Screw the new contactor in place.

• Reconnect wires exactly how the picture shows:

  • Line voltage on top

  • Load voltage on bottom

  • 24V coil wires on sides

6. Restore Power & Test

Turn the thermostat to COOL:

• The contactor should click closed.

• The outdoor fan and compressor should start.

⚠️ Safety Tips

• Capacitors can hold stored energy. Don’t touch the terminals.

• If you’re not comfortable working with 240V power, get a tech.

• Always verify power is off before touching anything.