Why would you pay for pipes and AC? That's not your responsibility. Even if you accidentally did something to damage it. If you took a saw and decided you didn't like the air con and made it into 100 pieces, then maybe you can pay for something but then again there is depreciation. If the air con was intentionally damaged by you, a 5k air con depreciated over 10 years would come down to like 500-1000 at most. And that's full replacement.
The landlord is smelling money and trying to take a piss as the Brits say. And why not, I don't blame them, easy target with previous success. No way you are getting your deposit back and good luck if you go to court trying to get the money. You might win, but collecting is another story.
End of story, the landlord will ask you to pay for repairs, and the tenant must not give in to this tactic. The tenant is not responsible to pay for such.