DC Motor power required

About 1/2 - 1 hp depending upon the total system efficiency.

I generally assume that using vapour compression cycle air conditioning or refrigeration one can get cooling capacity (Pc) of about 2.5 times as much as electrical power input (Pe). A quick look at two split units installed here at home gives Pc/Pe ratio of 6 kW/2.83 kW=2.12 and 6.76 kW/2.45 kW=2.75. I suspect large difference in two values may be in part as result of using different rating conditions i.e. indoor and outdoor conditions at which rating test is conducted. Admittedly a small amount of that electricity is used to turn indoor and outdoor fans. Your requirement is for Pc= 0.8x3.5 kW=2.8 kW cooling capacity. [1 ton equals approximately 3.5 kW]. Assuming you have a fairly efficient system and minimal transmission losses (belt drive or similar) I would think that you would be safe opting for something in excess of 2.8 kW/2.5=1.12 kW or 1.5 hp. Increasing motor capacity would also reduce risk of motor not being able to start turning compressor. Hope this helps. WR

What's the rating of the ac motor? What type of motor? Whats the starting method?Give more info on the existing drive..