When the outdoor unit hums but won't start, clicks, or runs without blowing heat out the top, the cause is often electrical: a failed capacitor, a stuck contactor, or a fan motor. Sometimes it's the compressor itself. Those are very different repairs, so getting a correct diagnosis matters. Requests sent through this site go to an independent HVAC contractor licensed by the Texas Department of Licensing and Regulation (TDLR). We don't perform repairs.
What these parts do
- Capacitor. Stores and releases energy to start and run the compressor and the outdoor fan motor. Heat is hard on capacitors, and they're one of the most common failures in a Texas summer.
- Contactor. An electrically operated switch that sends power to the outdoor unit when the thermostat calls for cooling. Contacts can pit, burn or get blocked by insects.
- Condenser fan motor. Pulls air through the outdoor coil to reject heat. If it stops, pressures climb and the system shuts down on safety or overheats.
- Compressor. The pump that moves refrigerant through the system. It's the most expensive component in the outdoor unit.
Typical symptoms
- Outdoor unit hums or buzzes, but the fan doesn't spin.
- The fan spins only after a push from a stick (don't do this; it's a sign of a bad capacitor or motor, and the unit carries high voltage).
- The unit starts, then trips the breaker.
- Indoor fan runs but the air is warm.
- Loud clanking, grinding or a hard "thunk" on startup.
Why you shouldn't open the panel
Capacitors can hold a dangerous charge even after power is shut off, and the outdoor unit runs on 240 volts. Replacement parts are cheap online, which is why forums are full of DIY advice. A wrong-rated part or a shorted connection can damage the compressor or injure you. The safe homeowner checks are limited to the thermostat, the indoor breaker, the outdoor disconnect and a clean filter.
Compressor problems
A compressor that won't start isn't always dead. A weak capacitor, failed contactor, or a lack of airflow can make a good compressor look bad. Before agreeing to a compressor replacement, it's reasonable to ask the technician which tests they ran, such as winding resistance, amperage draw, and pressure readings, and what they ruled out.
If the compressor has truly failed, the repair is significant. On a newer system it may be covered by the manufacturer's parts warranty if the equipment was registered. On an older system many homeowners compare the repair quote with a replacement. Getting a second opinion on a major repair is common and reasonable.
Preventing repeat failures
Electrical parts fail sooner when the outdoor coil is dirty, airflow is poor, or the unit has been short-cycling. A yearly AC tune-up that includes checking capacitor readings and cleaning the coil catches many of these failures before the hottest weeks.
How a request works
Describe the sounds and symptoms and roughly how old the unit is. We'll forward your request to an independent licensed contractor who serves your town, and they'll contact you directly to schedule and quote.
Compressor & Capacitor Repair FAQs
My outdoor unit hums but the fan won't spin. What is it?
A failed run capacitor or fan motor is a common cause, but it can also be a contactor or compressor issue. Turn the system off to avoid further damage and request a diagnosis.
Is my compressor really dead?
A bad capacitor, contactor or airflow problem can mimic a failed compressor. It's fair to ask which tests the technician ran before accepting a compressor diagnosis.
Is a compressor replacement worth it?
On a fairly new system under warranty, often yes. On an older system, many homeowners compare the repair with a replacement. A second opinion is common for a repair this size.
Why do capacitors fail so often here?
Heat and long run times wear them out, and Texas summers are hard on outdoor electrical parts. Checking capacitor readings is part of a good AC tune-up.
Is my compressor covered by warranty?
Many manufacturers offer longer parts warranties on compressors when the equipment was registered. Labor is usually separate. Check your registration with the manufacturer.