I was told I need a new capacitor for My Lennox Ac unit (10ACB24-11P) The capacitor is rusted on all sides and I don't know what the # is. By reading some previous questions it sounds like I need to get the correct one. Does anyone know where I can find out which one I need?

Look at the schematic. Sometimes it will give the capacitor size (in microfarads) and working voltage there. These are the two important numbers for that part. Also you must know if it is a starting capacitor or running capacitor. Two different animals. If the schematic doesn't help, find a local HVAC repairman and ask them your question. They will be able to help you. Some will get the part for you if you want to DIY. (Note: usually there is no warranty on electrical items for DIY work.) Others will want to do the whole service call. That way they might find out why the cap failed and repair that too and save you a second problem.

Can be dangerous,, be careful,it might pay to pay someone