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C1 DIAGRAM WITH B1 DIAGRAM
Electromechanical Thermostat Connected to GCS16-823 or GCS16953 (Without Economizer)
The diagrams in this section are used to represent the relationship of
GCS16 electrical components and to show the step by step sequence that
takes place when thermostat demand is sent to the GCS16. The operating
sequence describes the actions of devices in the unit which control blow
ers, fans and other components in the system.
A-GCS16-823, AND GCS16-953
Operation Sequence: C1 and B1 Sections (electromechanical thermo
stat wired to GCS16-823 or GCS16-953)
Power:
1- When the unit disconnect closes, line voltage energizes transformer T1
and the compressor crankcase heaters. Transformer T1 provides 24VAC
power to unit cooling, heating and blower controls and thermostat. The
crankcase heaters are powered at all times but are selfregulating
2- Transformer T3 (460V and 575V units) is also energized when power is
applied to the unit.
Cooling Demand:
3- On a call for first stage cooling (Y1), demand passes through the first
stage safety limits and energizes contactors K10 and K1. Both con
tactors immediately switch. At the same time, the indoor thermostat
energizes the indoor blower circuit (G). Blower demand passes
through blower relays K20 and K25 to energize indoor blower conta
cotr K3. K3 immediately switches.
4- When contacts K1-1 close, comrpressor B1 is energized immediately be
gins operating.
5- When contacts K101 close, condenser fan B4 is energized and the con
denser fan immediately begins operating. When K10-2 closes, the sec
ond stage cooling circuit is enabled. The purpose of the K10-2 circuit is
to prevent the second stage compressor from operating without a fan.
Each circuit is equipped with its own safety limits. The safety limits are
placed in the circuit so that when actuated, they only deenergize the
compressor they are connected to. An exception to this rule is compres
sor monitor S3. When S3 opens, both compressors and the condenser
fan are deenergized.
6- When contacts K31 close, the indoor blower is energized immediately be
gins operating. When K32 closes, a circuit is completed to the optional
economizer to open the outdoor air dampers to minimum position.
7- On a call for increased cooling (Y2), demand is passed through the second
stage safety limits to energize contactor K2. K2 immediately switches.
8- When contacts K22 close, compressor B2 is energized and immedi
ately begins operating.
Heating Demand:
9- On a call for first stage heating (W1), demand energizes combustion air
blower relay K13.
10- When contacts K131 close, combustion air blower B6 is energized and
immediately begins operating. When contacts K132 close, the gas
valve is enabled.
11- As the combustion air blower approaches full speed, combustion air
blower prove switch (S18) closes.
12- When S18 closes a 24VAC circuit is completed through the heating
safety switches to energize burner ignition control A3.
13- When ignition control A3 determines that ignition can begin, A3 simulta
neously sends 24VAC to the first stage operator of the gas valve and to
the indoor blower delay relay (K25) and also sends spark to the spark
electrode. The gas valve immediately opens and blower delay K25 im
mediately begins timing.
14- When flame is sensed by the ignition control, spark is stopped and the
gas valve remains open. If flame is not sensed within the time allowed,
spark is stopped, the gas valve is closed and the ignition control begins
its retrial timing sequence.
15- When blower delay K25 ends its timing period, K251 switches. A
24VAC circuit is completed through K201 to energize blower con
tactor K3.
16- When contacts K31 close, the indoor blower is energized immediately be
gins operating. When K32 closes, a circuit is completed to the optional
economizer to open the outdoor air dampers to minimum position.
17- On a call for increased heating (W2), demand passes through
K202 to energize time delay DL3. DL3 immediately begins its tim
ing sequence.
18- When DL3 time delay has elapsed, DL3 closes internally to complete a
circuit to the second stage operator of the gas valve (W2). When gas
valve operator W2 is energized, the gas valve begins to slowly open for
second stage operation.
19- If either heating limit S10 or S21 open during heating operation, ignition
control A3 is immediately deenergized and blower limit relay K20 is im
mediately energized.
20- When A3 is deenergized, the gas valve (W1) and blower delay (K25)
are both deenergized.
21- When K201 switches, blower contactor K3 is energized to continue blower
operation during the time that safety limits are open. When K202 opens,
second stage thermostat demand is prevented from reaching the second
stage operator of the gas valve (W2).
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