If you have questions about your Yaris, please sign up at
www.yarisworld.com/forums. We are more than gladly to help you out. As for your question, I'll hear my fans turn on when the A/C is in use, and I'll feel it, but my car does not shudder violently. If you know anyone else with a Yaris, ask them to turn on their A/C and you can compare yours to theirs.
-Kaotic Lazagna on YW.