Just make sure you know the law...
Withholding rent here can be risky and often provides the rent must be deposited with the court...
There is also repair and deduct a remedy that I seldom come across these days.
Plus, breaking the lease without penalty for habitability breech...
The poster has lots of options...
No A/C in January isn't likely to have the same urgency as August...
Always have to be careful because City-Data does not offer/provide legal advice...
Here is a link to the State of California website regarding repairs, rent withholding etc...
http://www.dca.ca.gov/publications/l.../repairs.shtml