Qmark MSPH - Plenum Rated Unit Heater - Manual (Page 3)

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CONTROL CONNECTIONS:
The PRH Series plenum heaters are designed to operate from
a 24VAC thermostat. Model TH5220D1003 24V 2 stage ther-
mostat is recommended to be used with the PRH Series
heaters. Thermostat connections are made to the thermostat
board located inside the unit. The thermostat label indicates
which connections are (RGCW) for making these thermostat
connections. The unit cabinet has a 3/8” knockout for routing
thermostat wiring to the units thermostat board (see
Specifications section for knockout location). Instructions for
wiring the thermostat are packed with the thermostat. The unit
is intended to operate with heat (W) and fan (G). If the unit is
intended for cooling signals from the thermostat, make the Y
connection from the thermostat to the G connection on the
unitʼs thermostat board.
UNIT OPERATION:
The PRH Series plenum heaters are intended to be operated
from a 24V thermostat. (Model TH5220D1003)
HEATING OPERATION
When there is a demand for heat, the thermostat sends a sig-
nal to the unit for this demand for heat. The unitʼs thermostat
board will send power to the unit controls to initiate the heating
operation. The call for heat makes the connection on the ther-
mostat board by powering “W” with “R”. Upon this demand for
heat, the heating element starts heating and the fan on delay
will power the fan within 60 seconds from the call for heat.
The fan delay ensures that there will not be a cold blast of air
to ensure comfort heating. When the heat demand has been
met, the thermostat will send the signal back to the unitʼs ther-
mostat board to stop the heating operation. This breaks the
power connection between “R” to “W” and the heating element
stops heating immediately. The fan off delay allows the fan to
continue running to remove all residual heat from the heating
element and will turn the fan off within 60 seconds. Should
there be any abnormal conditions to cause the units limit to
open during the call for heat, the units heat will turn off immedi-
ately but the fan will go through its normal off delay. During
this open limit period, the power to the thermostat will be inter-
rupted until the limit closes. This helps in determining abnor-
malities during heating operation by way of interrupting power
to the thermostat.
FAN OPERATION
When there is a demand for fan, the thermostat sends a signal
to the unit for this demand for fan. The unitʼs thermostat will
send power to the unit controls to initiate the fan operation.
The call for fan makes the connection on the thermostat board
by powering “G” with “R”. The fan will immediately come on
and continue to run until the demand for fan has ended. When
the fans demand has been met, the fan will immediately turn
off. This breaks the power connection between “R” to “G”.
HEATING OPERATION + FAN OPERATION
When there is a demand for both heat and fan at the same
time, the heating element will come on immediately as well as
the fan. The fan on delay will be bypassed. Upon completion
of the demand for both heat and fan, the heating element will
turn off immediately. However, the off delay will work the same
as during the heating operation.
COOLING OPERATION
Should the unit be used for cooling, the “Y” connection from
the thermostat should be connected to the “G” on the thermo-
stat board. The cooling operation will operate like the fan
operation above.
WIRING DIAGRAMS
Single Phase - Single Element Three Phase - Single Element 480V