Ac Compressor not turning on

Not much experience with the ac system as it is normally very reliable. You probably need to go to the toyota techinfo site and check the online repair manual for troubleshooting the ac system. Since it is a three phase electric compressor it is network controlled and has its own controller called an ac amplifier. I believe there is a diagnostic code accessible through special keypresses. Once you have those codes the online repair manual will decode them and how to proceed. The link gives more info on the techinfo site. Toyota Service Information and Where To Find It | PriusChat

The drawing below is from a 2012 gen 3 but will give you an idea of the sensor.
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Here is a procedure I located for getting the ac codes

TROUBLE SHOOTING
SELF-DIAGNOSTICS
An Electronic Control Unit (ECU) within A/C-heater control panel monitors system circuits and stores trouble codes in memory if problems are detected. All codes, except Codes 22 and 23, are stored in memory. Malfunction is current if Code 22 or 23 is displayed. To retrieve stored codes, see RETRIEVING CODES. Codes are displayed at temperature display.

RETRIEVING CODES
1) Simultaneously press and hold AUTO and RECIRCULATE switches on the steering wheel. Press Start and go to Ready. Turn AC on as some code appear only when running.
2) A/C system will enter self-diagnostic mode. To end indicator check, press and release OFF switch. Read codes at temperature display.
3) If trouble code is displayed, proceed to appropriate trouble shooting procedure. See DIAGNOSTIC CODE IDENTIFICATION table. Codes are displayed in ascending order.

Code Diagnosis
00 ................................................ Normal
11 (1) ............. In-Vehicle Temperature Sensor Circuit
12 (2) ................ Ambient Temperature Sensor Circuit
13 ................. Evaporator Temperature Sensor Circuit
14 .................... Coolant Temperature Sensor Circuit
21 (3) .............................. Solar Sensor Circuit
22 (4) .................... Compressor Lock Sensor Circuit
23 (4) ........................... Pressure Switch Circuit
31 .................. Air Mix Door Position Sensor Circuit
32 ................ Air Inlet Door Position Sensor Circuit
33 ............... Air Outlet Door Position Sensor Circuit
41 ....................... Air Mix Door Servomotor Circuit
42 ..................... Air Inlet Door Servomotor Circuit
43 .................... Air Outlet Door Servomotor Circuit

(1) - If in-vehicle temperature is -4 F (-20 C) or less,
Code 11 may set even though system is normal.
(2) - If outside air temperature is -58 F (-50 C) or less,
Code 12 may occur set though system is normal.
(3) - If testing is done in a dark area, Code 21 may set even though system is normal. Shine a light at solar sensor and recheck codes.
(4) - Malfunction is current. Code is not stored in memory.

ACTUATOR CHECK
1) Perform step 1) of RETRIEVING CODES. When system enters self-diagnostic mode, press recirculated air button. Each mode door, motor, and relay will operate at one-second intervals. Press fresh air button to display codes one at a time, and perform step-by-step actuator check.
2) Check airflow and temperature by hand. Tone will sound each time display code changes. Each display code is associated with a system operating condition. Press OFF button to cancel actuator check mode.

 

A little more googling:

“Not a good one. It says there is an A/C Inverter Load System Malfunction (code 76). This can be caused by a refrigerant leak or overfill, a problem in the condenser fan circuit, or lastly a compressor lock.”

...and

“When I brought it in for service, their first diagnosis was refrigerant loss so they attempted to bypass the low refrigerant failsafe. They couldn't get the compressor to cycle back on to take in more refrigerant and a leak detecting dye. So it is sort of pointing to the compressor being at fault.”

...and

“Compressor replaced, system evacuated and recharged. Tech said no debris noted in system flush. Cooling quite nicely now. New (used) compressor sounds quieter. I asked about what would be done with my old compressor and they said it would be returned as a core. Not torn apart to see what caused the failure.“

So its either take it in for a Toyota diagnosis, try to bypass the low pressure switch (find procedure at techinfo) and or go shopping on ebay (but somebody would still need the procedures). I think if it was the pressure sensor you would have seen code 22 or 23.