There is a speed sensor on the compressor, and the AC computer compares the
compressor RPM with engine RPM. If the difference is too great, like if the
belt slips after driving through a deep puddle, the system will disengage
the compressor and set the light to blinking. Turning the AC off and then
back on resets the system.
Another possible cause, and the one I think is likely on your car, is a bad
AC magnetic clutch relay. Technical Service Bulletin EL011-05, titled "A/C
Light Flashing - Magnetic Clutch Relay" covers this condition on, among
other vehicles, the 2004 Highlander.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.