Dexon Canada Air Systems Inc
OWMDH Series Use Manual
Version 07.2019
Page 4
3.1 SEQUENCE OF OPERATION
The main PCB inside the unit controls the blower heater functions, the fan and powers the
status board.
A temperature sensor at the discharge of the unit regulates the heating elements to maintain a
preset temperature that is based on airflow requirements and location.
In this series the heating elements are staged to reduce power consumption. Stages 2 and 3 will
only be activated and only remain on when stage 1 cannot meet the demand. Stage 2 and 3
LEDs will not blink but remain constant.
In “Auto” mode the fan will run continuous at an adjustable preset speed based on airflow
requirements and heating capacity of the unit; i
n “Manual” mode the fan will run at full speed.
When the discharge temperature drops below 0°C (typically) the unit will go into a
“Low Temp.”
shut down condition, shutting down the fan to prevent freezing of the ventilated space.
The unit will automatically restart when the discharge temperature r2°C (typically) or
more.
A built-in timer overrides this shut down for 7-8 minutes when the unit is manually reset or
power is cycled to allow the elements to warm up the discharge temperature. This override does
not apply when the unit automatically restarts after a
“Low Temp.” shut down.
If the discharge temperature rises above the normal operating range the unit will go into an
“Overheat” condition cutting power to the heating elements. After cooling down, the heating
elements will automatically restart.
Power to the heating elements will also be cut in the event of a fan failure
or a “Low Temp.” shut
down condition that caused the fan to shut down.
A fan failure will in
dicate a “Fan Stopped” status on the status board. If the optional alarm
module is used it will initiate a remote alarm even if there is no power to the status board.
3. CONTROL PRINCIPALS
CAUTION: Leaving the blower heater in “Manual” mode will drive the fan at full speed
and will override the “Low Temp.” shut down feature. The unit should never be left in
“Manual” mode since the heating capacity of the unit is based on preset airflow rate
and continuous duty in
“AUTO” mode.
