Why Do My Lights Flicker When the AC Kicks On?

A quick dim can be normal

When an air conditioner compressor starts, it pulls a large surge of current for a second or less. That can cause a slight dip in voltage, and your lights may dim for a moment and then settle. If it is brief, happens only at startup, and everything else in the house is fine, it is often just physics. It is worth noting, though, rather than ignoring. If you have lived with it for years and it has not changed, it is probably just how your house responds. If it is new, treat it as news. Mention it to us when you call, since a change over time is one of the most useful clues we get.

When it is not normal

Pay attention if the flicker lasts more than a second or two, keeps happening while the AC is running, or has become worse over time. Also watch for dimming that shows up when other things start, like the dryer, a microwave or a well pump. A pattern like that tells us something in the system is working harder than it should. Flickering in only one room is a different story. That often points to a single bad connection, a worn switch or a loose bulb socket rather than anything with the whole house.

Common causes we find

The most frequent cause is a loose or worn connection somewhere between the utility and your lights, in the panel, a breaker, a splice or the outdoor disconnect. Another is a circuit shared by too many things, so a big motor starting pulls down the lights on the same line. Older wiring and an undersized service can contribute. An aging air conditioner with a tired compressor may also draw more surge current than it used to. We see this most in older homes that have added central air since they were built, where the original wiring was never sized for it.

What you can safely check

You can do some careful noticing without touching anything electrical. Write down when it happens, which lights flicker, and whether it is the whole house or one room. Note if other appliances seem to trigger it. Check whether the air filter is clean, since a struggling AC works harder. That information helps us find the cause much faster, so jot it down before we arrive. A short phone video of the lights doing their thing is useful too. If a neighbor sees the same flicker at the same moments, tell us, because that points toward the utility side.

When to stop and call right away

Some signs mean do not wait. A burning smell, a buzzing or crackling sound from the panel or an outlet, an outlet or switch plate that feels warm, discolored covers, or any sparking all point to a connection that may be overheating. Do not open the panel or try to tighten anything yourself. Turn off the air conditioner if you can do so safely at its thermostat, and call a licensed electrician.

What we do on the visit

We start by asking about the pattern, then look at your panel, check for loose connections and heat signs, and measure the voltage while the air conditioner starts. Depending on what we find, the fix may be tightening or replacing a bad connection, moving the AC onto its own circuit, or recommending a soft start device for the unit. Occasionally the issue is on the utility side, and we will tell you how to report it. Either way you leave with an explanation, not just a bill.

If the cause turns out to be a worn air conditioner, we will say so and suggest you have an HVAC company check it. We would rather point you to the right trade than sell you work that does not solve the problem.

What it may cost

A loose connection repair is often a small job. A dedicated circuit or a service upgrade costs more, and the range depends on your home and your area. We give you a written price after we see the problem, and we will tell you if your situation is simply normal and needs nothing at all.