2001 chev tahoe has no power at a/c clutch checked fuses,relay,high pressure switch,low pressure switch and has 100 lbs of pressure on low side port

Bad clutch, wiring even bad ground.

Hard to say with just low pressure readings. But either the high pressure switch is bad or you are low on freon. If you want to know what is wrong I need the temperature of outside air, the low pressure reading and the high pressure reading as the compressor is running. But this only tells you ta particular problem. It won't tell you if you have a leak. This you have to find out on your own.

Make sure you are even getting power through your a.c. switch on the console. That sends power to the main relay and through the high pressure and Low pressure switch in series and then to your compressor clutch. Trace power through all of these and you will know which component is faulty.

Looks like the low pressure switch gets power from a 10amp ac fuse. Power then goes to the ac relay which is powered on by the ac heat controller on the dash. Power then goes thru the high pressure switch to the compressor. The ac relay is grounded to the body. Do you have power on the lite and dark green wires going into the relay and is it grounded ?

Put a jump wire in the high pressure switch plug. If the compressor works. replace the high pressure switch. Let me know and we can go from there.

"Most Fords have a CCRM (Continuous Control Relay Module) thats on the passenger side fenderwell. It has 4 relays: one for the AC compressor cluth, one for the fuel pump, and two for the electric fan (high- and low-speed.) The AC is the one that fails the most. You can replace the CCRM by removing the intake air filter box and working through the fenderwell openings. If it gets to difficult you must remove the wheel and splash cover to replace it from the wheel opening." - H-andy Mann

with the engine idling, tap on the ccrm and listen for the clutch to come on. if it comes on, you need to replace the entire ccrm.

CHECK REFRIGERANT CHARGE. USING A MANIFOLD GAUGE SET. HOOK MANIFOLD GAUGE SET TO LOW PRESSURE PORT AND HIGH PRESSURE SIDE PORT. LOW SIDE PRESSURE SIDE SHOULD HAVE 25 - 36 PSI AND HIGH PRESSURE SIDE SHOULD BE 178 - 237 PSI. IF LOW SIDE PRESSURE SIDE READ BELOW 20 PSI THE LOW PRESSURE SWITCH WILL NOT TURN ON THE AC COMPRESSOR CLUTCH NEED TO ADD LITTLE MORE REFRIGERANT. IF REFRIGERANT LEVEL CORRECT CHECK AC COMPRESSOR FUSE AND RELAY.IF POWER GOING TO AC COMPRESSOR CLUTCH YOUR COMPRESSOR CLUTCH HAS OPEN WINDING. AC COMPRESSOR CLUTCH NEED REPLACING.

Your A/C compressor clutch is controlled by the Electronic Climate Control Module (ECCM) via the compressor clutch relay. The low pressure switch only completes the circuit between fuse #A3 in the engine compartment fuse block to the high pressure switch, which in turn, completes the circuit to the control (or primary) side of the clutch relay. It does not provide direct power for your clutch. The primary ground side of the relay is controlled By the Powertrain Control Module (PCM).

If there is no power on either terminal of the low pressure switch, it can only be a blown 10 Amp fuse #A3 or a broken wire between the fuse and the low pressure switch. If the fuse is blown, replacing the fuse will not fix your car unless you find out and correct the reason why the fuse blew.

If this is not the problem, the only EFFECTIVE way to diagnose this system is to scan your computer system for fault codes and diagnose it accordingly.

Please also review these articles:
What Else Could Be Wrong?

Where's The Fuse?

FIRST I CHECK ALL FUSES AND RELAY.TO BLOWER MOTOR IF IT STOP BLOWING.AND CHECK FUSE TO HVAC SWITCH CONTROL.AND CHECK FUSE / RELAY TO AC COMPRESSOR.IF FUSE / RELAY GOOD POWER GETTING TO AC COMPRESOR CLUTCH COIL AND LOW PRESSURE SIDE 28 PSI AND HIGH SIDE 200 PSI. CLUTCH COIL IS OPEN.IF REFRIGERANT LEVEL LOW YOU MAY NEED MORE REFRIGERANT.YOU NEED AT LEAST 28 PSI ON LOW SIDE AND 200 - 220 PSI ON HIGH SIDE.IF ALL IS GOOD STILL NO AC PROBLEM COULD BE A FAULTY AC CLUTCH CYCLING PRESSURE SWITCH.

Freon is what you are missing, our more specificly a refigerant charge that exceeds 45psi on the low side pressure line. This system has two pressure switches, a high side cut-out switch mounted on the rear of the compressor, and a low side or pressure cycling switch on the suction line.
Jump the low side switch contacts to ensure the electronics are sound for this system. If the compressor cycles, you know the system is low on a refrigerant charge. Turning on the AC is a request, and certain criteria must be met before the system operates as designed. Good luck