A friend of mine has an window air conditioner unit in her apartment. Actually, its in the wall, not the window, but same concept. The unit isn't working and the landlord is saying that if she wants to use it, then it is her responsibility to get it fixed. It was working when she moved in, and had it not been, she would never have rented the place. The lease doesn't say anything about it being her responsibility. What, if anything, can she do?

(1) Send the landlord a letter certified mail telling him to fix the damn thing immediately. State that she will not pay rent for the remainder of summer if it isn't fixed, as this violates the "warrant of habitability" during the summer months.

(2) Withold rent in full until it is fixed.

The landlord absolutely is legally required to fix it. Your friend can definitely withold a significant portion of her rent in the mean time, and can probably withhold all rent for hot summer months.

It depends on her lease and if it says AS-IS, or if the air conditioner was an item that the landlord was to provide to the tenant as part of the lease. If it was not, the landlord can technically remove the air conditioner and still be compliant with the lease. If the tenant wanted the air conditioner to be provided as part of the lease, it should be spelled out in the lease.
I cannot see the lease so the best answer I can provide. I suggest consultation with a local attorney who can better interpret the lease. It really will depend on what it says.

ElkLaw - the warrant of habitability cannot be contracted around.

Also, even if it said "as is" the tenant still is entitled to have the landlord make repairs to keep the unit in the condition it was in when the tenant began renting.

An "As Is" clause would not waive the duty to repair. It just ensures that minimal warranties are made as the condition of the unit AT THE TIME OF RENTAL. So it would relieve the landlord of duty to repair pre-existing defects, but not new defects that arise during the term of the lease.

Thanks for your help...I'll pass this on to her.