You must replace it so your air conditioner or heat pump continues to work properly. The substitute capacitor must be able to handle the voltage. Start And Run Capacitor Explained Hvac How To 2020 Air Conditioner Repair Costs Average Ac Repair Cost Guide Air Conditioning Not Blowing Cold Replace Your Capacitor Or How to figure the capacitor size of an air conditioning unit ehow discover. What size capacitor do i need for my ac unit . A capacitor is used to supply this initial push to the motor. This is a general estimate not an exact figure. If you cannot get an exact size match to the original motor capacitor it is acceptable to use a capacitor rated one step higher in uf. Electric motor run capacitors are typically in the 2 uf 70 or 80 uf range of capacitance and their voltage rating will be 370 vac or 440 vac. The resulting number is the mi...