a/c works rarely. When it kicks on car loses power and noise comes from engine. Compressor kicks on and off and there is a clicking noise each time this happens.

Any Ideas?

Sounds to me like it needs recharged. The system needs to be charged correctly in order for it to run continuously.

+1^..Whoever decides to charge it I would have them add some dye to the system also...just to be prepared should the system ever develop a leak...

Sounds to me like its working fine. Is it not cold?

The Click you hear is the sound the clutch makes when it engages. There is also a relay for the clutch driver (the magnet) that you may hear click on and off.

The power loss is normal. That compressor takes a lot of power to turn. We're talking about a gas that is already pressurized to about 125 - 150psi when the system is just resting, and its being compressed even more (~250psi or higher) when the compressor is turning.

Disengagement of the compressor clutch, followed soon after by re-engagement, often indicates low refrigerant level.

 

However, another possibility is that there is a restriction in the system (clogged orifice, stuck-closed expansion valve, etc.). That can cause the compressor clutch to disengage shortly after engaging, but re-engagement takes longer because the restriction slows pressure equalization. It will also eventually minimize the oil in the compressor, which may then fail.