AC & HVAC Repair Hub

Run capacitors hold a lethal charge long after power is off. ALWAYS do this before touching terminals.

1. 1Kill power at the breaker AND pull the outdoor disconnect box.
2. 2Wait at least 1 minute — never assume the capacitor is dead.
3. 3Bridge a 15k–20kΩ 5W resistor across HERM→C, then FAN→C terminals for 5+ seconds each. (An insulated screwdriver works but is harder on the part.)
4. 4Verify with a multimeter on volts — the reading should fall to under 5V.
5. 5Never touch terminals with bare fingers or hold metal tools across them.

The #1 failed AC part — test it before replacing parts by guesswork.

1. 1Discharge the capacitor first (see the safety guide).
2. 2Set the multimeter to capacitance (µF mode).
3. 3Measure C→HERM (compressor side) and C→FAN (fan side).
4. 4Compare each reading to the label: within ±6% is good.
5. 5Replace with the SAME µF rating and equal-or-higher voltage. A reading of 0, a bulged top, or leaking oil means replace.

Example label: 45+5 MFD ±6% 440VAC.

1. 145 µF runs the compressor (HERM), 5 µF runs the condenser fan (FAN); C is the shared common terminal.
2. 2Match the µF ratings exactly. Voltage can be 370V or 440V — a 440V is always a safe replacement for a 370V.
3. 3Photograph the label and wiring before removing anything.
4. 4Universal dual-run capacitors are stocked at HVAC supply houses and are inexpensive — bring the old one or the photo.

The heavy relay that feeds the compressor and fan — easy to inspect and cheap to replace.

1. 1Power off and open the electrical panel of the outdoor unit.
2. 2Look for pitted, burnt, or welded contacts and insect nests (ants and lizards love contactors).
3. 3With power on and the thermostat calling for COOL, listen for the contactor to pull in with a clear click.
4. 4A contactor that hums but doesn't pull in, or clicks but passes nothing, needs replacing.
5. 5Match the replacement: pole count, amperage (e.g. 30A or 40A), and 24V coil voltage.

Every unit — 3-ton condenser to window box — has a data plate that tells you how to wire it.

1. 1MCA (Minimum Circuit Ampacity): the wire must be sized for at least this many amps.
2. 2MAX FUSE/BKR: the breaker must not exceed this size.
3. 3RLA (Rated Load Amps): normal running amps of the compressor.
4. 4LRA (Locked Rotor Amps): the startup surge — why AC breakers are allowed to be 'oversized' relative to other circuits.
5. 5Example: a 3-ton condenser might show MCA 19.9A / MAX 30A / 240V — #10 copper and a 30A double-pole breaker. Size from the plate, never by guesswork.

Window and through-wall units come in two voltages — the plug tells you which you have.

1. 1110/120V units up to ~15A use a standard NEMA 5-15 or 5-20 plug — a regular outlet, ideally on a dedicated circuit.
2. 2240V units use a NEMA 6-15P or 6-20P plug. It will NOT fit a standard outlet — that's by design. Never use an adapter; have the proper 240V circuit installed (see the Tools & Materials wire chart).
3. 3Never run any window unit on an extension cord or power strip.
4. 4If it trips a breaker at startup, compare the nameplate amps to the circuit rating and check what else shares the circuit.

Most 'broken' ACs are just dirty. This routine prevents the common failures.

1. 1Central systems: replace the 1–5 inch filter every 1–3 months during season.
2. 2Once a year, power off and gently hose the outdoor condenser coil from the inside out — keep 2 ft of clearance around the unit.
3. 3Window units: rinse the filter monthly; vacuum the front coil fins with power off.
4. 4Flush the central condensate drain with a cup of vinegar each season to stop algae clogs.
5. 5Test capacitors and inspect the contactor visually each spring — they're wear parts.

Get the right part the first time by bringing the right information.

1. 1Photograph the rating label of the old part (capacitor µF/voltage, contactor amps/coil volts) before removing it.
2. 2HVAC supply houses stock universal capacitors, contactors, fan motors, and float switches — often far cheaper than big-box stores.
3. 3For OEM boards, blowers, and ECM modules, the unit's model and serial number (on the data plate) is what the counter needs.
4. 4Refrigerant handling — recharge, leak repair, recovery — legally requires EPA 608 certification. Leave sealed-system work to a licensed tech.

A unit's watt draw while cooling is simply BTU/hr ÷ SEER.

Example: a 3-ton (36,000 BTU/hr) unit at SEER 14 draws 36,000 ÷ 14 ≈ 2,570 watts. The same unit at SEER 22 draws ≈ 1,640 watts — about 36% less electricity for identical cooling.

Annual energy: kWh = (BTU/hr × cooling hours) ÷ SEER ÷ 1,000. Use the calculator below to run a real customer's numbers.