I have a Krystal bus with both front and rear AC. On the control panel above the driver head I have a master switch for HEAT/COOL/OFF and a separate HI/LOW/OFF for each AC. I also have a knob that cab be turned to control the AC temperature. Is this knob for both AC's or just the rear? Also does the driver area have to be turned on for the front AC in the passenger are to work? Lastly I hear people talk about valves that have to be turned when going from heat to AC...is this true if so where are these valves located? Thanks in advance for all the help.