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C3 or C5 DIAGRAM WITH D8 DIAGRAM
Flexstat or Prostat with Three-position Economizer
2-C3 or C5 Section with D5 Section
An EMDH16 or REMD16 economizer may be applied to a GCS16 with Flexstat or Prostat.
Both are programmable thermostat which allow GCS16 units to automatically setback or set
up setpoints for unoccupied periods as well as control setpoints more precisely than electro
mechanical thermostat. With the economizer added, the Flexstat is capable of directly control
ling the operation of outdoor air dampers.
NOTE - In order to understand how these optional controls affect the operation of the GCS16,
you must first understand how all GCS16 components work. Refer to the operation se
quence for basic unit operation.
NOTE - These thermostats have a built-in clock for controlling setback. Optional time clock
CMC3-1, night thermostat and night relay kit are not needed and are not compatible.
No wiring is required when connecting an economizer. Economizer plug P4 connects to
GCS16 jack J3 in the unit blower compartment. Jumper-plug P3 is removed and discarded.
See figure 92.
IMPORTANT - Flexstat model L2F has been superseded by Flexstat L2F-N. Terminal desig
nation on the two controls are different. This sequence of operation describes models L2F-N.
Refer to Table 23 for more information.
Operation Sequence:
1- Economizer outdoor air dampers drive full closed anytime blower B6 is not operating.
2- The GCS16 with Flexstat or Prostat is designed so that the fan switch in the thermostat is to be
left in the ON mode at all times. This allows the blower to be controlled by terminal 4 inside
the Flexstat (G in Prostat). The blower operates continuously during occupied periods
and intermittently (only during demand) during unoccupied periods.
NOTE - Flexstats ONLY: If slide switch number 7 on back of model L2F-N (slide switch num
ber 5 on back of L2F) is switched to ON position, the blower operates continuously during
occupied periods and automatically cycles during unoccupied periods. If this slide switch is
switched to OFF position, the blower operates normally during unoccupied periods, con
trolled by the ON/AUTO button on the face of the control.
3- During a heating demand when the building is not occupied, the blower is activated only when
a heating demand passes through relay K25 in the GCS16. During a cooling demand when the
building is not occupied, the blower is activated through terminal 4 in the Flexstat (G in Pros
tat).
4- Setback relay K11 ( not furnished) is not used in this application. Contacts K11-1 and K11-2 (if
installed) are normally closed and should remain closed at all times.
Heating Demand:
5- Heating demand (Prostat terminal W1 - Flexstat terminal 2) activates the GCS16 heating sec
tion directly.
6- Additional heating demand (Prostat terminal W2 - Flexstat terminal 3) is not used in this ap
plication.
7- Economizer outdoor air dampers remain at the mid (minimum) position allowed by the mini
mum positioner during blower operation.
Cooling Demand Enthalpy Low:
8- Enthalpy control internal relays switch to close a circuit from 1k terminal 1 to 6 and from 2K
terminal 3 to 5.
9- Initial cooling demand (Prostat terminal Y1 - Flexstat terminal 5) is routed through enthalpy
control terminals 1 and 6 and through discharge air thermostat S13 to energize enthalpy con
trol terminal D and damper motor terminal D. 24VAC applied between damper motor terminals
D and T energizes the damper motor and the outdoor air dampers open fully.
10- Economizer outdoor air dampers drive full open during blower B3 operation (anytime there is a
cooling demand)to provide first stage cooling. Outdoor air dampers drive full closed anytime
blower B3 is not operating.
11- Additional cooling demand (Prostat terminal Y2 - Flexstat terminal 7) is routed through enthal
py control terminals 1 and 2 to energize the compressor. The compressor provides all addi
tional cooling.
Cooling Demand Enthalpy High:
12- Enthalpy control internal relays switch to close a circuit from 1k terminal 1 to 2 and from 2K
terminal 3 to 4. Outdoor air dampers close. Dampers open to minimum position during blower
B3 operation.
13- Cooling demand (Prostat terminal Y1 - Flexstat terminal 5) is routed through enthalpy control
terminals 1 and 2 and terminal 5 to energize the compressor. The compressor handles all cool
ing demand.
14- Blower demand (Prostat terminal G - Flexstat terminal 4) energizes blower relay K3 in the unit.
Contacts K3-1 close to energize the blower and contacts K3-2 close to energize the econo
mizer. When 24VAC is applied between enthalpy control terminals X and T, the outdoor air
dampers open to mid (minimum) position. Dampers remain open when blower B3 is operating
and close when B3 is not operating.
15- Increased cooling demand (Prostat terminal Y2 - Flexstat terminal 7) is not used in this ap
plication.
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