Chris is getting you on the right track. Setting your AC temp dial would likely get the temps you want for fermenting ales.
For lagering or cold crashing you are going to want colder temps than the AC is designed to run so you are going to need to hack it a bit. First remove the front cover and you will find one or two temp sensors. One sensor will be attached to the temp dial. To trick the dial into thinking the cooling is required get this sensor outside your chamber in to warmer air. Many of these ACs also have a second sensor attached to the cooling coils that will shut down cooling if the coils are icing up. Get that sensor somewhere warmer if it is shutting down your AC, but then you do need to figure out how to deal with the icing.