Onida W112yr 1 Ton Ac review: Not giving proper cooling

I bought 1 ton onida ac model W112 YR on4-5-2010 from Khurana Electronics main bazar, Moga-142001 Punjab on the pursuance of the dealer that it would give perfect cooling to the 12ft. long and 10ft. wide room. I had to install it by my own when the dealer said that they had no arrangement to install it, despite the fact that it is clearly written in the booklet that the ac should be installed by the authorised dealer.
Now the ac is not giving proper cooling and it is consuming 1.75 unit per hour.I complained to the dealer. He sent mechanic who checked the ac and said that ac is fitted correctly and working properly but the room is not suitable for ac.
Now i want to know whose fault it is? It is duty of the dealer to check the location of the site where ac is to be installed and should install by his mechanics before sending the ac to the customer's home.