Rev. December 19, 2008
Page 10 of 19
# 1 Frequency Setting - Set to ON (down) for 60 Hz service. This includes all of North America. Set to
OFF (up), for electrical grids using 50 Hz.
#2 Defrost Type - ON (down) is for damper/recirc. models. OFF (up) is for fan shut down defrost
models.
#3 Fan Selector - OFF (up) is for the NU075 machine only. All other models are set to ON (down).
#4 Arctic Mode Selector - for design temperatures of -30 0C (-22 F) and colder for Damper/recirc.
defrost machines, or design temperatures of –20 0C (-4 F) and colder for FSD defrost machines, set to
Off (up). Otherwise set to ON (down). When the machine is set to operate in arctic mode, the machine
will increase the amount of time spent in defrost.
Variable low-speed motor control:
For field adjustment of the low (continuous) ventilation rate, pushbutton switches S1 & S2 are used.
These are located on the bottom left of the board. S1 is labeled DEC (decrease) and S2 is labeled INC
(increase). Each push of S1 or S2 decreases or increases low speed by increments of 3%. Low speed is
set at 40% of high speed in the factory by default and cannot be lowered beyond this point. The
maximum low speed setting is approximately 70% of high speed. Settings are stored in the board’s
memory, eliminating the need to reset the speed after a power failure for instance.
Self-resetting fuse:
Field mis-wiring of timers or dehumidistats may cause the fuse to trip. If this happens, remove the
control wires and allow the fuse to reset. This may take a few minutes. Check your manual for proper
wiring connections.
Troubleshooting using the PCB light:
There is a small green light on the board located just below the DIP switches. This light will either be
solid or pulsing and is an indicator of machine status. It can be used to assist in troubleshooting
.
Machine State
Light Status
Machine has no power
Off
Power to the board, but main power switch is off
or the door switch is tripped
Two short pulses approximately every 5 seconds
Machine running normally in low speed
Pulsing – on for one second, off for one second
Machine running in high speed due to a call from
dehumidistat, timer, or defrost cycle
Solid
Defrost Cycles:
Fan Shutdown Defrost – On FSD machines, the temperature sensor is located in the fresh air stream
before the core. When this air is measured to be below freezing, a timed defrost cycle is initiated. The
fresh air fan motor is stopped for 4 minutes (both normal and arctic modes). The exhaust fan motor
continues to operate, drawing warm air from the building through the core. After 4 minutes, the fresh air
fan motor is started again and runs for 20 (normal mode) or 12 (arctic mode) minutes. This cycle is
repeated until the temperature of the exhaust air stream is measured to be above freezing.
