Specifications

Page 35
C1 DIAGRAM WITH B2 DIAGRAM
Electromechanical Thermostat Connected to GCS24-1603 (Without Economizer)
Operation Sequence: C1 and B2 Sections (electromechanical thermostat wired to
GCS24-1603)
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 self
regulating
2- Transformer T3 (460V and 575V units) is also energized when power is applied to the unit.
Blower Operation:
3- Blower demand from thermostat terminal G energizes blower contactor K3.
4- N.O. K31 closes, blower begins operation. N.O. K32 closes energizing economizer damp
er motor (if economizer is installed, outdoor damper drives to minimum position).
1st Stage Cooling (both compressors B1 and B2 operate separately):
5- Cooling demand energizes Y1 and G in the thermostat. G energizes blower (see step 3.)
6- 24VAC power is routed through N.C. high pressure limit S4, N.C. freezestat S49 and N.C.
low pressure limit S87, and 12 minute delay shunt DL26 to energize compressor contactor
K1 and pilot relay K27.
7- N.O. Contacts K1-1 close energizing compressor B1.
8- N.O. pilot relay K127-1 closes allowing 24VAC to pass through the N.O. low ambient switch
S11 to energize condenser fan contactor K10.
9- N.O. Contacts K10-1 close energizing condenser fan B4.
2nd Stage Cooling:
10- Second stage cooling demand energizes Y2. 24VAC power is routed through high pressure
limit S7, freezestat switch S50, low pressure limit S88, and 12 minute delay shunt DL27 en
ergizing compressor contactor K2 and pilot relay K128.
11- N.O. contacts K21 close energizing compressor B2.
12- N.O. pilot relay K128-1 closes allowing 24VAC to pass through the N.O. low ambient switch
S84 and N.C. low ambient thermostat S41 to energize condenser fan contactor K68.
13- N.O. Contacts K68-1 close energizing condenser fan B5.
1st Stage Heating:
14- On a call for first stage heating (W1), demand energizes combustion air blower relay K13.
15- When contacts K131 close, combustion air blower B6 is energized and immediately begins
operating. When contactst K132 close, the gas valve is enabled.
16- As the combustion air blower approaches full speed, combustion air blower prove switch
(S18) closes.
17- When S18 closes a 24VAC circuit is completed through the heating safety switches to ener
gize burner ignition control A3.
18- When ignition control A3 determines that ignition can begin, A3 simultaneously 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 immediately begins timing.
19- 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.
20- When blower delay K25 ends its timing period, K251 switches. A 24VAC circuit is completed
through K201 to energize blower contactor K3.
21- When contacts K31 close, the indoor blower is energized immediately begins operating.
When K32 closes, a circuit is completed to the optional economizer to open the outdoor air
dampers to minimum position.
2nd Stage Heating:
22- On a call for increased heating (W2), demand passes through K202 to energize time delay
DL3. DL3 immediately begins its timing sequence.
23- 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.
24- If either heating limit S10 or S21 open during heating operation, ignition control A3 is immedi
ately deenergized and limit relay K20 is immediately energized.
25- When A3 is deenergized, the gas valve (W1) and blower delay (K25) are both deenergized.
26- When K201 switches, blower contactor K3 is energized to continue blower operation during the
time that safety limits are open. When K202 opens, second stage thermostat demand is pre
vented from reaching the second stage operator of the gas valve (W2).