And Yes, an important thing to note for ensuring leak tightness of Inner Unit!
Now a days, DC Inverter Split ACs inner units (I am not sure regarding non-Inverter ones) are leak tight and pressurized (i.e. some gas / air is filled inside them with pressure). They have some sealed knobs at the ends. When a technician is about to install inner unit of AC and make connection with the pipes, as soon as he opens the knobs, bohat zoor sey air k bahir nikalnay ki awaaz aati hai, like; thaa kar k ya jaisay tire puncture hua ho.
Agar aesi awaaz aye, to samajhein k aapka inner unit bilkul leak tight hai and agar kal ko gas ki leakage hoti hai, to wo pipes waghaera ki wajha sey ho sakti hai (like installation proper na hui ho, ya connection pipes faulty hoon), but inner unit ki wajha sey nai.
Agar knobs kholein aur koi b awaaz na aye entrapped air k nikalnay ki, one can assume that the inner unit is not leak tight, and it may be damaged / faulty (one way or the other)! 
