Your air conditioner is a mechanical system run by an electrical one, and when it quits on a Triangle afternoon, the cause is more often electrical than mechanical. That is mostly good news. The electrical parts inside a cooling system are among the least expensive to replace. The catch is that they are also the parts that ruin the expensive mechanical ones when they are left alone. This post follows the path electricity takes through your system and points out where it tends to fail. It also explains which of those failures are ours to fix and which belong to an electrician.
Following the power from the panel to the compressor
Electricity reaches your air conditioner through a dedicated breaker in the panel, then a disconnect box on the wall near the outdoor unit, then a contactor inside that unit, which is a relay that closes when the thermostat calls for cooling. From the contactor, power flows to the compressor and the outdoor fan motor, with a capacitor giving both the push they need to start. Indoors, a transformer steps household voltage down to the low voltage the thermostat and control board use, and thin wires carry the thermostat’s signals to both units. Every one of those pieces can fail, and many of them fail in ways you can recognize.
Where it goes wrong
The capacitor
The capacitor is the small metal cylinder in the outdoor unit that stores a charge and releases it to start the compressor and fan. It is the single most common electrical failure in an air conditioner, and heat is what wears it out. The signs are an outdoor unit that hums without the fan turning, a system that takes several tries to start, or a click that repeats without the compressor kicking on. A weak capacitor makes the motors draw more current on every start, so a small part becomes a large one if it waits.
Contactor wear
The contactor’s contacts arc a little every time they close, and over a long cooling season they pit and burn. A worn contactor may chatter, so the system stutters on and off, or stick closed, so the outdoor unit keeps running after the thermostat is satisfied and the house gets colder than you set it while the bill climbs. Ants are drawn to the small electrical field around a contactor and are a common cause of failure in this region when they are crushed between the contacts.
Connections
Every wire in the system ends at a screw or a push-on connector, and those connections loosen with years of vibration and corrode in Triangle humidity. A loose connection creates resistance, resistance creates heat, and heat melts insulation. The signs are a system that works some days and not others, or a burning smell near the unit. Tightening and cleaning connections is a standard maintenance item, and it is the quiet reason maintained systems rarely have electrical fires.
The thermostat and its wiring
A blank thermostat display usually means dead batteries or a tripped breaker on the air handler. A system that ignores the thermostat entirely often has a broken low-voltage wire, a loose connection at the terminal strip, or a wire outside that a string trimmer or an animal has damaged. A smart thermostat that reports faults will often tell you which of these it is before the house has warmed up.
The control board and transformer
The control board takes the thermostat’s signal and decides what to turn on and when, and the transformer feeds it low voltage. Both are vulnerable to the voltage swings that come with Triangle thunderstorms and with power returning after an outage, and both can fail after a nearby lightning strike even when nothing else in the house was touched. A system that does nothing at all, with good batteries and closed breakers, often has one of these two parts to blame.
Problems that are not inside the system
Not every electrical problem that stops an air conditioner lives inside it. On a hot afternoon when every house on the street is cooling at once, utility voltage can sag enough to stall compressors and trip breakers. Surges when power returns after a storm damage capacitors and boards across a whole neighborhood. And problems in the home’s own electrical panel, such as a failing breaker, undersized wiring to the unit, or a panel that cannot carry the load, are electrical work rather than air conditioning work. Happy Home Services covers the cooling system and its dedicated circuit. When the fault is in the panel or the house wiring, our technician will tell you plainly and recommend a licensed electrician, because that is the right person for the job.
What to watch for
- A system that hums without starting, or takes several tries.
- A breaker that trips more than once.
- Any burning smell near the indoor or outdoor unit.
- Lights that dim when the outdoor unit starts.
- A unit that keeps running after the thermostat is satisfied.
Every one of these is inexpensive when caught early and becomes a compressor when it is not. Our maintenance visits test the capacitor under load, inspect the contactor, and tighten connections every time, which is how these problems get caught before they have the chance to grow. For a failure that has already happened, air conditioning repair starts with the electrical readings, since that is usually where the answer is.
We are here when it quits
Happy Home Services has been Durham’s trusted heating and air experts since 1955. If your air conditioner has stopped, reach us 24/7 by phone or website chat, and the technician will find the failed part, explain it, and give you the price before replacing it, with honest, upfront pricing with a 100% money-back guarantee. Members of the Happy Home Service VIP Club receive priority, same-day service when summer fills the calendar.