YORK INTERNATIONAL
54
Sequence of Operation
FORM 100.50-NOM1 (604)
Space Sensor Control (RTD)
Under space sensor control, the Primary Unit Controller
will monitor the space temperature via the space sen-
sor inputs and the Occupied input and control the unit
ac cord ing ly. The use of a space sensor on a constant
volume unit re quires an unoccupied/occupied signal to
the controller. This signal can be received from one of
three sources: the hard-wired Unoccupied/Occupied
input, internal scheduling via a Network (BAS), or
from a roof link controller. The unoccupied/occupied
signal de ter mines what programmed space temperature
setpoint to maintain in the controlled space.
For this option to function the con
Þ
guration setting
Space Sensor Enable must be set to ON and the sensor
must be reliable. During this mode of operation, if the
space sensor becomes unreliable, a fault will be gener-
ated. With this, the unit will shut down unless a RAT
(return air temperature) sensor is enabled and reliable.
If a RAT sensor is present, the unit will monitor the
Return Air Temperature for unit control decisions. If
the RAT sensor then becomes unreliable, the unit will
be shut down.
Types of Space Sensors
No Sensor –
The con
Þ
guration setting,
"Space Sensor
Enable"
, Must be selected OFF. The Control will only
operate the unit from the Thermostat inputs or from a
network (BAS).
Sensor Only –
This Sensor only has a RTD in it for
unit op er a tion.
• Y1 Off – shut off Cooling Stage 1 – All compressor
operation will be shut down
Heating Operation with W1 and W2 Inputs
The Primary Unit Controller can be con
Þ
gured for four
types of heat, Gas, Electric, Steam, Hot Water. When
Gas or Electric is selected, the unit must also be con-
Þ
gured for the number of stages. The Hot Water and
Steam options use a modulating valve that varies the
heating capacity based on the load. A Modulating Gas
Heat option is also available. When Modulating Gas
Heat is installed, the unit is con
Þ
gured for Hot Water.
• W1 Active Only (Staged Heat) – One half of the
total number of stages will be energized See Table
15.
• W1 Active Only (Modulating Heat) – The Primary
Unit Controller will modulate the valve based on
the temperature difference between the Supply Air
Temperature (SAT) and the “Hydro Heat 1
ST
Stage”
set point.
• W1 and W2 Active (Staged Heat) – All the stages
will be energized.
• W1 and W2 Active (Modulating Heat) – The Pri-
mary Unit Controller will modulate the valve based
on the temperature difference between the Supply
Air Temperature (SAT) and the “Hydro Heat 2
ND
Stage” set point.
• W2 Active Only (Staged Heat) – Only the W2 heat
stages will be energized. See Table 15
• W2 Active Only (Modulating Heat) – The Primary
Unit Controller will modulate the valve based on
the temperature difference between the Supply Air
Temperature (SAT) and the “Hydro Heat 2
ND
Stage”
set point.
As the Heating Stages are de-energized, or if steps of
heat should be dropped due to Excessive SAT (supply
air temperature), the steps of heat will be de-energized
one at a time. If the unit is not equipped with heat, the
control will ignore the W1 and W2 inputs.
Gas or Electric (Stepped) Heating
If the controller is con
Þ
gured for stepped heating, the
controller will read the Heat Steps con
Þ
guration set-
ting to determine the number of heating steps available.
Up to six (6) individual heating steps can be available.
These steps will be divided into two Heating Stages as
shown in Table 15.
TABLE 15 – STAGED HEATING STEPS
Sequence of Operation
TOTAL #
OF
STEPS
AVAILABLE
# OF STEPS ASSIGNED TO
HEATING STAGE 1
HEATING STAGE 2
1
1
0
2
1
1
3
2
1
4
2
2
5
3
2
6
3
3