Step 3: Verify that the Compressor is Running
1. Start the engine
2. Turn the A/C on
3. Turn the fan to maximum
4. Follow the hose from the low side fill port to a cylindrical device attached to the engine - this is the compressor
5. Locate the pulley on the compressor.
6. Is the center part of the pulley spinning?
Yes. Then the compressor is engaged, as it should be.
No. Add half of a can of r-134a as detailed in the manner described in the upcoming steps. If the compressor still fails to engage, take your vehicle to a mechanic.
7. Leave the engine running and the A/C on maximum until you are finished with the entire filling process.
The photos depict the compressor in its engaged and disengaged states.