Replace a Contactor (Condenser)

De-energize and verify 0 V, match the pole count (1 vs 2), the 24 V coil voltage, and the FLA/resistive amp rating, photo the wiring, land line/load (T1–T2) + the 24 V coil leads, check for pitted/welded contacts as the failure cause, then verify pull-in and the voltage drop across the contacts.

Approx. 40 min

Before you start

•Contactor confirmed as the fault: pitted/burned/welded contacts (unit won't shut off, or chatters), an open/burned 24 V coil (won't pull in), or a mechanical stick — verified with a meter.
•Replacement contactor that matches: pole count (single-pole vs double-pole), the COIL voltage (almost always 24 V on residential), and an amp rating (FLA/resistive amps) equal to or greater than the load.
•Power can be killed at the disconnect + breaker before opening the panel.

Tools & materials

Multimeter (verify 0 V, coil ohms, contact voltage drop) · Nut drivers/screwdrivers · Replacement contactor (matched poles/coil/amps) · Phone camera (photo wiring before)

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Isolate & verify dead

Pull the disconnect, kill the breaker, verify 0 V
Pull the condenser disconnect and switch off the breaker, then verify 0 V across the line terminals (L1–L2) AND from each leg to ground before touching the contactor. Bleed the run capacitor too.
Tools: Multimeter
⚠ Lockout/tagout and verify 0 V — the contactor line side is energized even with the thermostat off until you pull the disconnect.
Inspect the old contacts for the failure cause
Look at the contacts: pitted, blackened, or welded-shut contacts confirm why it failed (and a welded contactor is why a unit 'won't turn off'). Note it so you can spot a root cause (low voltage chatter, ant/critter, undersized contactor).
Target: Pitted/welded/burned contacts = the failure; note any root cause

Match & wire

Photograph the wiring and match the replacement
Photo every lead first. Confirm the new contactor matches the pole count (1 vs 2), the 24 V coil voltage, and an amp rating ≥ the original. A single-pole only breaks one leg — don't sub it where a double-pole is required.
Target: Poles (1 vs 2), 24 V coil, amp rating ≥ original — all matched
Land line, load (T1–T2) and the 24 V coil leads
Mount the new contactor and reconnect per your photos: line voltage to the line side, the compressor/fan loads to the load side (T1–T2), and the two 24 V coil leads to the coil terminals. Torque the lugs so nothing arcs loose.

Verify pull-in & contacts

Restore power and confirm it pulls in on a call
Re-energize, call for cooling, and confirm the contactor pulls in cleanly (no chatter) and drops out on satisfy. Chatter usually means low 24 V or a weak coil.
Tools: Multimeter
Target: Clean pull-in on call, clean drop-out on satisfy; 24 V at the coil ≈ 24–28 V
Measure the voltage drop across the contacts
With the unit running, measure the voltage drop across each closed contact (line-side to load-side of the same pole). A meaningful drop means resistance/pitting and heat — a good closed contact drops near zero.
Tools: Multimeter
Target: Voltage drop across each closed contact near 0 V (a high drop = bad contacts/heat)