Hi Dana I have a Cessna 182 that I installed a Westach carb temp gauge and sensor in because I fly some hard IFR.
Westach tells you that you should start worrying about carb ice at 10 degrees Celsius and recommends you apply enough carb heat to keep the carb above that temperature. That being said, I don't think it would be unreasonable to set your yellow limit at 10 degrees C. The red limit could be at somewhere in the 1-5 degree area. One clear 55 degree F day, I took off from my home airport and was climbing over the nearby lake. My carb temp dropped to 0 degree C in about 15 seconds over that lake. It was a very interesting lesson on how humidity can radically change your carb temp. Brant Hollensbe West Des Moines, Iowa
