Air con problem on my 1999 20v

Hello,
I own 1999 20v Coupe and I have a problem with air con. It is working well for some time when I turn it on, but after a while it stops working with full strength. When it doesn’t work well the air compressor clutch is engaging and disengaging every 2-4 seconds, then I turn off the ac and turn it on again and it starts working fine again for some time, about 20-30 minutes.

The system is well gassed. I’ve changed the three stage pressure switch and relay and the problem won’t go away. All the wires looks fine.

Please help.

Thanks in advance.

Cona.