Is anyone here familiar with Armstrong (Lennox) equipment? I have recently purchased a 3-ton 13SEER Armstrong heat pump to replace our old 8SEER system. Overall, I am pretty happy with the new pump. The outdoor unit (2SHP13LE136) is quiet and generates enough heat to keep the house warm down to about 25oF outside. It came with a variable speed air handler (EVF16CCP-1A), a modular coil (EC1P36CG-1), and a 20kW electric furnace (10kW x 2 with separate breakers).
The trouble starts when the thermostat calls for auxiliary heat (when it gets colder or during the defrost cycle). The 4-ton blower (Ύ hp ECM motor) produces the max airflow of 1,600 CFM. The contractor said this much air is required to prevent the new heat strips from melting (the old air handler had an 18.5 kW heater and it did just fine at much lower CFM). We have uninsulated sheet metal ductwork in much of the house and the noise the new blower creates is very annoying. When the air rushes through the 6 round ducts at 8,000 FPM into our living room it sounds like a jet during takeoff. Closing the dampers and registers on those ducts doesnt make much difference (I am thinking about replacing them with R8-insulated flexible ductwork).
Since we use only one of the two 10kW strips (it works fine even when the outside temperature drops to 0oF), I tried to adjust the maximum blower speed down to 1,200 CFM. I set the jumpers in the motor control board to D position (see Figure 2, Page 6 of the attached manual), which corresponds to 1,200 CFM based on the information in Table 3 (page 7). I also disconnected the W wire from the motor control board, because the contractor said it switches on the relay that overrides the jumper settings on the board. All to no avail. There is a LED on the board that flashes once for each 100 CFM. When the furnace is on, the CFM LED is flashing 16 times and the motor is going full blast
I would appreciate any suggestions.