a/c problem

[PR CB7]

well guys, im working on a 91 cb, and compressor wont engage by it self, when 12v is applied to compressor and i turn the fans on, everything works, pressures are perfect, temps are great, but it wont do it on its own

things i've checked:
thermoswitch works
dual pressure works
both relays work
clutch works
a/c light turns on
replaced diode with 2 other

the only thing that gave me hope was, i put ground to the blue/black wire that goes to the A/C diode and BAM, idle goes up, compressor engages, fans turn on
but if i try to drive with it, it will blow the a/c fuse in the dash fusebox
i need some help guys
thanks

[visualpoet]

Have you checked the HVAC control switch and the wiring from there to the relay? If everything past the relay works, the problem must be before that.