The breaker keeps tripping.

A breaker trips when current exceeds what the circuit is rated for. That is the whole mechanism. So the question is never really “why did the breaker trip”, it is “what is drawing too much”.

Reset it once. If it trips again, stop resetting it. You are overriding the device that is trying to prevent an electrical fire, and the information it is giving you is worth more than the next hour of cooling.

The cheap causes

A failed capacitor. A motor that cannot start draws locked rotor current, several times its normal running draw, for as long as it keeps trying. That alone will trip a breaker, and it is the most common cause in a Phoenix summer.

A contactor with welded or badly pitted contacts. Arcing across a damaged contact surface is both a current problem and a heat problem.

A filthy condenser coil. This one surprises people. A compressor that cannot reject heat runs at higher pressure and draws more current, all day, every day. A coil clean can genuinely stop a nuisance trip.

Each of those is a flat price well inside the one thousand dollar ceiling that applies here.

The expensive causes

A failing motor. Worn bearings mean more current to turn the same load. Fan motors are on the price list.

A compressor drawing high amps or going to ground. A compressor that has shorted to the chassis will trip a breaker instantly and repeatedly. This is the one that ends in a replacement conversation, and it is past what can be done here.

The ones that are not the AC

A weak breaker. They age, especially after repeated trips.

A wiring fault. Rodent damage to the whip between the disconnect and the unit is common enough to be worth looking at, as is a loose lug cooking its connection.

Both are electrical work rather than HVAC work.

What a diagnosis actually involves

Amp draw on the compressor and both motors under real load, microfarads on the capacitor against its rating, voltage at the unit while running, and a look at the contactor, the wiring and the coil. You get those numbers written down.

That matters here more than usual, because the difference between a capacitor and a compressor is the difference between a flat price and a new system, and you should not have to take anybody’s word for which one it is.

While you wait

Leave the breaker off. A system that trips repeatedly is not cooling your house anyway, and each failed start is hard on the compressor. If the house is getting dangerous and somebody vulnerable is in it, that is a different problem and worth saying on the phone.