Help! Power question

pcc67

On the main breaker 200amp you have 2 legs off that ...  If both the ac breaker and the breaker feeding the outlet you are having issues with are on the same leg, this may be the issue with the drop in power. You are drawing current off the same leg. Balancing would put both circuits on opposite legs ... I also have central ac ... No issues.

In the US, most central A/C units are 240VAC. That means it would be connected to both legs of the electric service.

Cleeds, 
At the main breaker the load is split, 2 separate bus bars each caring 120 volts. When you add a 30 amp double pole breaker you have 2 hots coming out, each hot out is 120. 30 amp double pole is like using two 15 amp singles, each single is 120. When add together that equals 240.  You dont need to be on 2 separate bars to get this. the double pole breaker is on one bus bar using 2 spaces.  I live in the US.  Electrical is a hobby of mine for 25 yrs.  I've have run electric for 2 ac in the past 2 yrs.  I believe his wiring is correct or he would be popping the breaker. I believe the load is very heavy on one bus bar, which is fine. But he can balance it by putting the problem circuit on the opposite bus bar. When ac kicks on, the load will pull from opposite bus bar. Both circuits pulling loads from 2 separate legs. 240 come in at top of panel and splits, 120 each side. If this is new compressor it should have soft start built in. If not have a starter kit installed,  but I would go first solution, balance. Good luck Pete 

I will correct myself. The double pole is taking from both sides. But u should still Check and make sure it is balanced and you don't have all 30, 40 and 50 amp circuits on one side, which would cause phasing issues.

@pcc67 it is clear that you are pretending to know much more about electricity than you really do. Please, before you get yourself or someone else hurt due to misinformation, stop promulgating this nonsense. The “phasing” issues you are yammering about are imaginary. Perhaps you’ve confused this with three-phase, where phase imbalance can occur, but all domestic electrical service in North America is known as “split phase”, the secondary is center-tapped. The center tap is known as neutral, and is bonded at the service panel to earth ground.  By the way, circuits over 20 amps are usually 240 volt circuits, which uses both legs, and therefore are inherently not creating an imbalance.