A/c Compressor Not Coming On - Relay 30 Ground?

[donzech]

2000 GMC K2500 (old style). A/C compressor is not coming on. If I short 85 and 86 where the A/C relay plugs into, the compressor comes on. 87 has battery voltage on it whether the A/C switch is on or off. 30 has a small floating voltage, whether A/C switch is on or off. I don't have a wiring diagram to go by, but I'm assuming that 30 should ground out when the A/C switch is on?

 

Is there anything between the dashboard switch and the relay? Can the switch be replaced individually or are the heating/cooling controls an entire unit?

 

Thanks

[donzech]

I guess I should also ask which circuit the low pressure switch interrupts? The control side or the high current side? I guess I was assuming it's the high current side....