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C19 DIAGRAM AND B34 DIAGRAM AND D8 DIAGRAM
Limited Commercial Application
Basic Electromechanical or Electronic Thermostat
Connected to Residential Horizontal-Only Unit (GCS16H)
with RDE16 and Three-Position Economizer
2- C19 SECTION and B34 SECTION with D8 Section (commercial application of elec
tromechanical or electronic thermostat wired to residential unit with three-position
economizer)
GCS16H units, even though not equipped for commercial use, may be converted to commer
cial downflow use in a special limited application. The application requires use of RDE16-41
roof duct enclosure to convert the unit to downflow use. The RDE16-41 includes a factory
installed harness for connecting optional REMD16-41 or REMD16M-41 economizer.
NOTE - The RDE16-41 economizer harness is represented in diagram C19. The economiz
er harness and jack J3 are located inside the RDE16-41, not inside the unit as in other
GCS16 commercial units. REMEMBER, this is a limited application converting a residential
unit to commercial use.
The harness (shown in diagram C19) has pigtails on the unit end and harness jack J3 on the
economizer end. The unit end of the harness hard wires to the unit and thermostat with pigtails.
Economizer jack J3 at the end of the harness connects directly into economizer plug P4. Field
wiring is shown in more detail in figure 59.
This particular application connects the REMD16-41 three-position economizer to the
GCS16H. The RDE16-41 return air side panel is removed and the REMD16-41 slides into the
side of the cabinet (same as it would into the side of a commercial GCS16). Economizer har
ness jack is located in the return air compartment of the RDE16-41. This installation is shown
in figures 92 and 57.
Operation Sequence:
1- Line voltage energizes transformer T1. Transformer T1 provides 24VAC power to all unit con
trols and thermostat.
2- Heating demand initiates at W1 in the thermostat and energizes relay K13. Heating demand
also passes through high temperature limits S10 to combustion air prove switch S18.
3- Relay K13 terminals 4-7 close to energize combustion air blower B6. Terminals 6-9 close to
energize the economizer (commercial units only). When the combustion air blower nears full
speed, prove switch S18 closes. Heating demand continues through S18 and through high
temperature limit S47 to energize ignition control terminal 1.
4- Ignition control A3 then waits 30 to 40 seconds to allow combustion air blower B6 time to draw
exhaust gas from combustion chamber and to introduce fresh air. Combustion air blower B6
operates throughout the heating cycle.
5- After the ignition control delay, A3 activates gas valve GV1, time delay K25 and the spark elec
trode. When flame is sensed by the flame sensor (minimum 5 microamps) the spark electrode
stops. If flame is not sensed after the first trial for ignition, controller A3 repeats steps 4 through
5 up to two more times (depending on controller make) before locking out. Delay relay K25
delays 60 seconds before closing.
If the control locks out, it can be reset by breaking and remaking thermostat demand.
6- After the 60 second delay, relay K25 closes to energize the indoor blower on heating speed.
I. Enthalpy Control in Low Position (outside air can be used for cooling).
First stage cool (all models):
7- Initial cooling demand Y1 is sent to enthalpy control A6 terminal 1.
8- Enthalpy control A6 has determined that outside air can be used for cooling and has switched
internal 1K and 2K internally.
9- Cooling demand is routed through enthalpy control terminal 6 and through discharge air ther
mostat S13 to enthalpy control terminal D and damper motor terminal D.
10- When 24VAC is applied across terminals D and T of damper motor, the damper motor ener
gizes and outdoor dampers open fully. First stage cooling is provided by outdoor air.
11-Thermostat terminal G energizes relay K3. K3-1 closes to energize the indoor blower and K3-2
closes to energize the damper motor.
2nd stage cool (all models):
12- Economizer outdoor air dampers remain open.
13- Additional cooling demand is routed from thermostat Y2 through enthalpy control terminals 3
and 5 to energize contactor K1. The compressor provides all additional cooling.
14- K1 is a single pole contactor, allowing compressor terminal R and one leg of the condenser fan
to be powered at all times. K1-1 closes to energize compressor terminal C, condenser fan
motor and the run capacitors for each motor. Condenser fan and compressor immediately be
gin operating.
II. Enthalpy Control in High Position (outside air cannot be used for cooling).
Cooling:
15- Enthalpy control internal relays 1K and 2K switch. Voltage across D & TR drops out while
voltage across X & TR continues. Outdoor air dampers close to minimum position.
16- Cooling demand is sent from thermostat terminal Y1 through enthalpy control terminals 1 and
2 and through enthalpy control terminal 5 to energize the compressor. The compressor han
dles all cooling demand.
17- K1 is a single pole contactor, allowing compressor terminal R and one leg of the condenser fan
to be powered at all times. K1-1 closes to energize compressor terminal C, condenser fan
motor and the run capacitors for each motor. Condenser fan and compressor immediately be
gin operating.
18- Thermostat terminal G energizes relay K3. K3-1 closes to energize the indoor blower and
K3-2 closes to energize the damper motor.
Night Setback (optional field installed-steps not shown on diagram)
19- Optional field installed time clock (not shown), night thermostat S12 and night relay K11 must
be connected for night setback operation.
20- Blower B3 operates only during a heating demand when night thermostat is closed.
21- When clock contacts close (not shown), relay K11 energizes. Contacts K11-1 open to disable
the day thermostat and contacts K11-2 open to drive the dampers full closed.
22- (Not shown) Night thermostat S12 is typically set with setpoints below thermostat S1. During
unoccupied periods, K11-1 opens while S1 is disabled. When S12 closes, power is supplied to
S1 and the unit operates normally. When S12's setpoint is reached, S12 opens, S1 is disabled
and unit operation stops.
23- Shortly before the building is to be occupied, clock contacts open to de-energize relay K11.
Contacts K11-1 close to restore power the thermostat S1 and Contacts K11-2 close to restore
power to the minimum positioner. Outdoor air dampers open to mid (minimum) position during
blower operation.
