I have a 30 amp circuit breaker to my central air unit. It worked just fine last summer. This summer it started tripping the breaker. I changed the contacts just in case that was the problem. This worked for a couple months. Now, it is tripping again. Could it be the breaker is worn out? Please help. Thanks.

I changed the contacts just in case that was the problem.

What are contacts? There is a item called a contactor in the outside unit is that what you replaced?

Many items can cause a circuit breaker to trip on over current.

A circuit breaker will weaken if it trips and has to be reset to much. The bimetal in the breaker weakens and causes this.

The unit outside could be

Overcharged with refrigerant.

Coils dirty

Out of range run capacitor.

Unit needs a hard start kit

Loose or damaged wiring anywhere from the unit to the house panel.

Short cycling

There are a few more but I think you get the idea.

You may have to get a on site professional who has the proper tools to figure it out.