I prospect using Google Earth and Windows Live Maps. You can determine the size of units from looking at them on the satellite view (birdseye view is great), in combination with the size of the building. Generally 1 ton of ac for every 500 square ft of space.
3 ton condenser is a single layer coil and can be THOROUGHLY cleaned in less than 4 minutes. Thus, $20.00. The larger the unit, the more the cost. In four years, whether it is filter cleaning or coil cleaning we only have a handful of accounts that generate less than $200.00 per hour. Our best one is $430 per hour for filter service, but they are happy to pay it because of the difficult roof access.
There is a building out here with over 500 6 to 10 ton units that I am trying to get.
The large unit we are cleaning in the video with the 90 degree tip pointing up takes 1 1/2 hours to clean and we charge $600.00 for that. There is a mall here with 26 of those units and another brand new mall we are bidding this month with about 35 of them.
We're not going house to house and cleaning individual units.