Nordic AH4P Series, Service Manual

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5-Jul-2022 Page 8 002596MAN-01
Thermostat Requirements
(-VSP models)
For –VSP models (e.g. AHW-65-VSP-...), the thermostat
or controller does not call for one discreet airflow value, but in-
stead uses a 0-10VDC signal to call for any airflow between 0
and 2500 cfm.
The airflow will be proportional to the DC input signal. For
example, a 5VDC input will result in an airflow of 1250 cfm re-
gardless of backpressure from the ductwork and air filter; and a
10VDC input signal will result in an airflow of 2500 cfm. (In
practice, airflows above 2300 cfm will likely be limited by the
maximum torque output of the blower motor, so will be less
than their nominal value.) Refer to airflow tables in the Model
Specific Information chapter for airflows with the various input
signals.
Note that if a 24VAC water valve connected between V
and V1 is to be opened, a dry contact between R and G must be
made at the same time as the DC airflow signal. This G call is
not
required for airflow.
Auxiliary heat may be called for by making a dry contact
from R to W
2
, which will activate the plenum heater relay and
turn on the plenum heater through terminals C
P
and 1 . Note
that for internally installed plenum heaters, at least 500 cfm
airflow must be called for at the same time by the 0-10VDC sig-
nal to run the blower and prevent plenum heater high tempera-
ture safety trips. More airflow will be required for externally in-
stalled heaters (as installed for AH4P-series) since the duct area
will be larger and airflow distribution over the duct cross section
will be more uneven; an airflow resulting in an air velocity of at
least 400 ft/min at the elements is required.
A motor speed output on the terminal RPM
OUT
is available.
This is a pulse output with 36 pulses per revolution. For exam-
ple, there will be:

120 pulses per second at a motor speed of 200 rpm

240 pulses per second at a motor speed of 400 rpm

360 pulses per second at a motor speed of 600 rpm

480 pulses per second at a motor speed of 800 rpm
Note that because of the constant airflow functionality, motor
speed will vary with duct and air filter backpressure at any given
airflow.
TABLE 5 - Control Signal Description
(-VSP Models, 0-10VDC Operation)
Signal Description
C 24VAC Common (Ground)
R 24VAC Hot
W
2
Auxiliary heat
G Water valve open
0-10
VDC+
Airflow demand signal 0-10VDC
GND Ground for airflow demand signal
RPM
OUT
Motor speed output (36 pulses/revolution)
V
24VAC water valve
V1
C
P
Plenum Heater dry contact
(Connect to C or I in plenum heater)
1
Plenum Heater dry contact.
(Connect to 1 and 2 in plenum heater)
Water Valve Control with AH4P-Series
It should be noted that if an AH4P-series air handler is to
be used for heating or cooling duty (rather than dehumidifica-
tion), the two water valves will have to be controlled by the ther-
mostat or controller directly. This is because there is only one
water valve connection point in the air handler.
For dehumidification duty, both water valves may be con-
nected to the same terminals in the air handler to provide simul-
taneous operation.