If your vehicle is showing a/c button light flashes or blinks continuously, here are the most likely causes and the parts you'll need to fix each one.
The relay that sends electrical power to the A/C compressor clutch frequently fails or sticks. When the climate control module detects that the compressor isn't engaging as commanded, it flashes the A/C light. This is an extremely common and inexpensive fix, especially on Toyota and Lexus vehicles.
If the drive belt turning the A/C compressor is loose, glazed, or worn, the compressor won't spin at the correct speed. The A/C system's speed sensor detects this slip and flashes the light to prevent further damage.
The clutch magnetically engages the compressor to the engine's drive belt. If the clutch coil weakens, the friction surface wears out, or the air gap becomes too wide, it will slip. The system detects the RPM mismatch and triggers the flashing light.
If the system loses refrigerant due to a leak, the pressure switch will disable the compressor to protect it from running dry. On many vehicles, this safety lockout is communicated to the driver via a blinking A/C button light.
If the compressor internally locks up due to lack of lubrication or mechanical failure, the clutch cannot spin. The system detects the speed mismatch immediately, disengages the clutch, and flashes the light to prevent the drive belt from snapping.