The power to my A/C and heater control has gone away. I have power at the fuse block but none at the control switch. No A/C or heater blower at all. I traced the brown wire from the fuse block to what I think is called the A/C Master Relay which is mounted on the passenger side of the firewall in the engine compartment. The line coming in from the fuse block has power but no power comes out. Thinking it was a bad relay, I installed a new one but still nothing. I tested the relay on the work bench and could not get it to open so I sent it back and got a new one. Still no power comes out. so I am thinking that the relay must need to be triggered by something else. I'm pretty sure my A/C system is full and even if it was not, wouldn't the heater blower still come on? I have the original shop manual but there is no wiring diagram of the heating/ A/C system so I can't tell where to trace this down. I suspect this is a simple fix if I only knew where to look. Anyone have experience with this? Thanks in advance.