A/C defaults to heating any time brakes or applied all the way to a stop or any time a big bump is hit. I also do not have any temp control its either full cool or full heat. When it defaults to heat I must turn fan speed all the way down and turn system completely off to get it to blow cool again.

 

Check all your vacum lines, hose to brake booster etc, if you don't find any problems maybe it's in the vacum part of the switches