The info plate on the air handler installed with my Trane A/C system says it is a TWE030P13BO. When cooling capability diminished after several years, due to a loss of 4 lbs of refrigerant, an independant technician (son of a friend) recharged it and also said he increased the fan speed of the air handler, which seemed evident by the small increase in the sound it made. Now, two years later, the sound from the fan has increased even more. So, I thought I would look for the switch that controlled the fan speed and set it to the lower speed. Not seeing it on the unit itself, I went to the installers guide and users manual, neither of which said anything about the fan. So I went to my best friend--Google--and came to realize my model is not supposed to be variable speed. So my question is, how did that guy change the fan speed?