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C4 or C6 DIAGRAM WITH D5 DIAGRAM
FLEXSTAT or PROSTAT WITH MODULATING ECONOMIZER AND WARM-UP
5- C4 or C6 Section with D5 Section
Optional Flexstat or Prostat programmable thermostats allow GCS16 units to automatically
setback setpoints for unoccupied periods as well as control setpoints more precisely than
electromechanical thermostats. With modulating economizer and warm-up kit added, Flexstat
and Prostat are capable of directly controlling outdoor air damper operation. The warm-up kit
holds outdoor air dampers full closed while warming the building after night setback.
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.
WARNING - CONNECT ONLY RELAY KITS DESIGNED FOR THIS CONTROL SYSTEM.
RELAY KITS DESIGNED FOR OTHER CONTROL SYSTEMS ARE NOT COMPATIBLE
AND CONTROL DAMAGE OR FAILURE WILL RESULT. FOR EXAMPLE, NEVER CON
NECT A W973 RELAY KIT TO A FLEXSTAT OR PROSTAT CONTROL SYSTEM.
WARNING - BE CAREFUL TO CONNECT RELAY KITS TO THE PROPER JACK AND
PLUG IN THE GCS16 BLOWER COMPARTMENT. REFER TO WIRING DIAGRAM. IM
PROPER CONNECTION WILL CAUSE CONTROL FAILURE.
The warm-up kit mounts in the control mounting area of the blower compartment (see figure
96). Some field wiring of the warm-up kit is required (refer to unit wiring diagrams on opposite
page). GCS16 unit jumper plug P3 is removed and discarded. Warm-up kit harness plug P8
connects directly into jack J3 in the blower compartment. Warm-up kit harness jack J8 con
nects to economizer harness plug P4. Relay K42 is not used in this application.
IMPORTANT - Flexstat model L2F has been superseded by Flexstat L2F-N. Terminal desig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.
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.
Operation Sequence:
1- Economizer outdoor air dampers drive full closed anytime blower B3 is not operating. Damp
ers also close during unoccupied periods and during morning warmup. Dampers open to
minimum position during all other unit operation.
2- Economizer relay K11 is not used in this application (not furnished).
3- The Flexstat and Prostat are designed so the thermostat fan switch 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 Pros
tat). The blower operates continuously during occupied periods and intermittently (only during
demand) during unoccupied periods.
4- During heating demand when building is unoccupied, blower is activated only when heating
demand passes through relay K25 in GCS16. During cooling demand when building is unoc
cupied, blower is activated through terminal 4 in Flexstat (G in Prostat).
First Occupied Heating Demand of the Day (Morning WarmUp):
5- Initial heating demand (Prostat terminal W1 - Flexstat terminal 2) activates the heating section
of the GCS16 directly and relay K40.
6- Contacts K40-1 open to keep relay K41 deenergized. Contacts K41-3 remain open to keep
outdoor air dampers closed during initial heating demand.
7- When heating demand is satisfied, unit gas valve and relay K40 are deenergized.
8- Contacts K40-1 close. Contacts K42-1 are already closed (not used in this application).
9- Time delay DL7 begins a 30 second count before closing.
10- If a second heat demand reaches relay K40 within 30 seconds, contacts K40-1 open, time
delay DL7 loses power and resets and the economizer is locked out for the 2nd heating de
mand. Steps 5-10 repeat. Outdoor air dampers remain closed.
11- If a second heat demand does not reach relay K40 within 30 seconds, time delay DL7 closes,
relay K41 energizes and contacts K41-1 and K41-3 close to lock in the economizer for the day
(until blower B3 stops). Outdoor air dampers open to minimum position allowed by minimum
positioner during blower B3 operation. Outdoor air dampers close when blower B3 is not oper
ating.
Occupied (Day) Cooling:
12- When thermostat switches to occupied (day) mode, blower B3 is energized in continuous
mode through unit terminal strip terminal TB1-G.
13- Terminal TB1-G also routes power through contacts K40-1 and K42-1 to time delay DL7. Time
delay DL7 begins a 30 second count before closing.
14- After 30 sec.,time delay DL7 closes to allow relay K41 to energize.
15- When relay K41 energizes, contacts K41-1 close to lock in economizer until blower stops
(night setback). Contacts K41-3 close to allow power to the economizer.
Cooling Demand Enthalpy Low:
16- Enthalpy control internal relays switch to close a circuit from 1k terminal 1 to 6 and from 2K
terminal 3 to 5.
17-Cooling demand (Y1 in Prostat - 4 in Flexstat) is routed through enthalpy control terminal 1 to
energize internal relay 1S. Contacts 1S1 close to energize damper motor. Outdoor air damp
ers open to provide first stage cooling.
18- Increased cooling demand (Y2 in Prostat - 7 in Flexstat) is routed through enthalpy control
terminals 3 and 5 to energize the compressor. The compressor handles all additional cooling
demand. Outdoor air dampers remain open.
Cooling Demand Enthalpy High:
19- 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
operation.
20- 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.
21- Blower demand (from Flexstat terminal 4 - Prostat terminal G) energizes blower relay K3 in
unit. Contacts K3-1 close to energize blower and contacts K3-2 close to energize damper
motor terminal TR. When 24VAC is applied between damper motor terminals TR and TR1,
outdoor dampers open to minimum position. Dampers remain open when blower B3 is operat
ing and close when B3 is not operating.
22- Increased cooling demand (Prostat terminal Y2 - Flexstat terminal 7) is not used in this ap
plication.
Unoccupied (Night) Operation:
23- Flexstat terminal 4 (G in Prostat) deenergizes. Blower B3 is deenergized and relay K41 is
de-energized. Time delay DL7 opens and resets. Outdoor dampers drive full closed.
24- When relay K41 deenergizes, Contacts K41-1 open to unlatch relay K41 circuit. Contacts
K41-3 open to lock out economizer operation during unoccupied period.
25- Unoccupied heating demand (Prostat terminal W1 - Flexstat terminal 2) energizes relay K40
and GCS16 heat section. Contacts K40-1 open to unlatch relay K41 circuit (operates like
morning warm-up).
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