Tahoe Heating problem

I have a 2001 Tahoe and the rear heating and A/C doesn't work. There are two switches one in the back seat and one above the center console. When trying to operate the rear A/C nothing happens except a clicking noise. I removed the whole right rear side of the interior and isolated the clicking to a relay. This relay only has 3 wires, an orange for power, a black for the ducting solenoids that operate the vents, and a purple for the motor. I disconnected the motor and the clicking continues. The ducting solenoids work fine and turn with both of the switches. I bought a new relay from the Chevy dealer (different brand name and model) and the same clicking is produced in the new relay. The motor works fine, I tried it on an external battery. Does anyone have any ideas??? Is there a fuse that's blown somewhere?? I have measured the power wire and read 11.6 volts. Doesn't seam to me like a power problem....maybe a sort somewhere, I don't know....help please????

I had the same problem with my 2001 Tahoe. For some unknown reason that I still have not been able to duplicate a fuse in the engine compartment blew. It is a 30 amp I believe. There should be a spare in the compartment.