This is a outside package electric 3 ton/ lp gas unit. D1np036n07206. I had unit setup and a ac installer check system in orginal install in oct. 07. It was "new" but did not cool properly, had it charged with ?3lbs? freon. It seemed to work great. I replaced a inside mobile home furnace with this unit. It took the place of the ouside packaged ac and inside furnace. I removed a second set of add on ducts that looped the home from ac to heater to one branch of duct to loop to second branch of trunk. was a very poor and cobbled up mess of fittings sizes and steel and flex duct. I now have the mobile homes orginal two trunk lines. I have a steel round 14" or maybe 16" return of about 20 feet then it changes to fexduct to connect to the unit. The supply is 12" flex which "t"s into the two trunk lines. I have all the register vents open in the floors. NOW THE PROBLEM The blower has a constant fluctuation during the heat cycles. It is not terribly pronounced but it would be like a constant 500 rpm drop and cycle again. No real mechanical motor noise, just a up and down low roar. The manual gives me a location of the dip switches but it appears to control the blower delay on or off time, not the blower speed. of course I could be completely wrong. The install told me they control the speed, the manual gives caution as to register air temps and blower speeds. I have a ac/heat temp gauge and electronic experience. Any advice on switch setting and heat temps would be appreciated or maybe I am not close to the real problem?