Have Toyota Questions? Ask a Mechanic for Answers ASAP
Thank you for allowing me to help you with this concern today and am sorry to hear that this is happening. I will have to ask you a few questions so that I can get a better understanding as to what may be going on with your Prius.
If you stop and then restart the Prius, does the a/c start working again? (even for a short time?)
Ok, this is a sign that either the Clutch Relay is bad or the Revolution sensor inside the Compressor is bad. Obviously the clutch relay is much cheaper and usually the culprit. Most of the time, if it is the revolution sensor, it's because someone installed an aftermarket compressor.
To replace the relay, look in the black colored fuse junction box, under the hood, along the drivers side front fender and locate the relay labeled CLR MG Relay. They run about $80 the last time I installed one. What happens is that the relay heats up and "opens" when it isn't supposed too. The a/c amplifier sees the compressor stopped turning, when it is supposed to be turning, and interprets, this as the drive belt is slipping (like you drove through a large puddle of water) and turns the system off then blinks the light to warn you.
Does this make sense?