Land Rover Repair: Climate Control, occational, climate control

Question
1998 P38 4.0   Problem with passanger side climate contol switching from a/c to heat and vise versa. Switches occational; but, book light comes on when changing most of the time. Compressor was bad, so replaced it and dryer.  Added 3 12 cans of R34A and adequate oil.  Need put gages to get precise amount of freon.  Would a little low on freon cause problem with changing from cold to hot?  Drivers side works perfect.  

Answer
Your passenger side problem has nothing to do with refrigerant level.  You probably need new servos.  There is a set of three servo motors (changed together) that regulate the temps on each side.  Common failure.  About a day's work to change them.  You get into extensive dash disassembly, so you should read the workshop manual before proceeding, but that's almost surely the issue on the right side