Repairs

You could fix it on your own

don't use it

get a portable unit

or get your landlord to fix it

Air conditioning is not something a landlord must provide. If it is part of the lease or was advertised and provided from the start of the lease. The landlord would be required to maintain it in working order. I would advise you to first call him and then send him a letter, in this regard, stating the problem.

Maintain Facilities: The landlord is required to maintain in good and safe working order and promptly repair all electrical, plumbing, sanitary, heating, ventilating, air conditioning, and other facilities and appliances supplied or required to be supplied by the landlord. But the landlord need not perform this duty unless the tenant first advises the landlord of needed repairs in writing. The tenant may wish inform the landlord of the problem immediately over the telephone or in person and then follow up by notifying the landlord in writing. The tenant should always keep a copy of all written communication between herself and the landlord.

In the event of an emergency, such as when the heat fails during the winter, prior written notification is not required. The landlord must tend to emergency repairs as he becomes aware of the problem, regardless of whether the tenant has given written notification. And if the tenant repairs an emergency problem, the landlord must reimburse the tenant, regardless of prior notice.

The laws differ regarding lack of repair issues vary from state to state, check out this link and find your state's law.
http://www.rentlaw.com/landlord.htm