Nissan Repair: Airconditioning problem & noisy belting sound & noisy sound underneath back area., gas leaks, nitrogen gas

Question
I own a unit of nissan serena c.c 2000, 4wd , diesel.
1.My problem is - almost every six month i have the air conditioning problem. The blower is running normally but not cold. Can you passs some knowledge of the simple air conditioning system to me (servicing/repair/troubleshooting)
2.How to solve belting noisy sound.(cik..cik..cik..cik..)
3. There is a noisy sound at the back area(underneath)it sound like spring.(nyit...nyit..nyit) when ever come across bumpy area. ?

Answer
The airconditioner is probably cycling due to low refrigerant.  I would correct the problem by filling the system and performing a leak check.

The rear noise is probably due to a bad strut.  They get noisy when the nitrogen gas leaks out and they get some excess play inside.  You get this clicking sound.  Now, it could be as simple as an exhaust hanger being broken.  These look like really large rubber bands that the exhaust hangs from.