The lights dim every time the AC kicks on.

When a compressor starts, it draws locked rotor current for a fraction of a second, which can be five to eight times its normal running draw. That brief surge pulls voltage down slightly across the whole house, and incandescent and some LED fixtures show it as a dip.

A quick, shallow dip you barely notice is ordinary physics, particularly on an older electrical service.

When it is worth attention

It got worse. This is the useful one. A house that always dipped slightly and now dims hard has changed, and something caused that.

The dip lasts. A momentary blink is the start. Half a second or more of visible dimming means the motor is taking too long to get going.

Flickering while running, not just at start. That is a different problem and points at a connection rather than inrush.

Anything else at the panel. Warmth, a burning smell, a buzzing breaker, or a breaker that trips. Stop and get an electrician.

The HVAC side of it

A failing capacitor. This is the common one. A motor with a weak run capacitor takes longer to get up to speed, so the high current period stretches out and the dip deepens. It is also the cheapest thing on the list, and the capacitor guide covers the other symptoms that travel with it.

A compressor that is tired. Worn bearings mean more current and a longer start. Measurable as amp draw.

A pitted contactor. Poor contact means resistance at exactly the moment the most current is flowing.

A hard start kit can genuinely help here, by shortening the moment of peak draw. It is one of the legitimate uses for one, and it is not a substitute for finding out why the start got worse.

The electrical side, which is not HVAC work

Loose connections. At the breaker, at the disconnect, or in the whip to the unit. Resistance at a loose connection makes heat, and heat makes the connection looser.

A loose or failing neutral. This is the serious one. A compromised neutral on the service makes voltage swing between circuits rather than just dip, and it can damage electronics and start fires. The tell is lights brightening somewhere while dimming elsewhere, or dimming that has nothing to do with the AC.

An undersized or overloaded service. An older Valley house with an original panel and modern loads on it.

Utility side problems, which neither you nor an HVAC technician can fix.

All of those are an electrician’s work. This business does not do electrical panel or service work, and you will get told that plainly rather than sold something adjacent.

A sensible order

1. Note what changed and when. Is it worse than last summer?
2. Have the AC side measured. Capacitor microfarads, amp draw at start and run, contactor condition, voltage at the unit under load. That is a diagnostic, and it either finds a cheap cause or rules the system out.
3. If the system measures fine, get an electrician. Having the HVAC readings in hand makes that visit shorter and cheaper, because they are not starting from nothing.

If anything at the panel is warm, buzzing or smells hot, skip to step three today.