After 50K, the a/c is acting up. It works for about 20 minutes and then the A/C lights starts blinking and the cold air stops blowing. I've read elsewhere on other Toyotas that the flashing indicates an electrical problem. Perhaps unrelated, a few months ago the gearshift light became unreliable and eventually failed completely. Any suggestions on what to check before putting myself at the mercy of the dealer? I can handle fuses and so forth, but much beyond that, I have no experience. Thanks!

Update: took the car into the dealer. Did not seem to be a problem they were familiar with. After some online searching, they decided to replace the compressor/clutch/sensor, which is a single part, at a cost of about $1100 with labor & recharge.