Lennox GCS16-823

Page 69
C1 DIAGRAM WITH B2 DIAGRAM
Electromechanical Thermostat Connected to GCS16-1603 (Without Economizer)
C-GCS16-1603
Operation Sequence: C1 and B2 Sections (electromechanical ther
mostat wired to GCS16-1603)
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 ap
plied to the unit.
Cooling Demand:
3- On a call for first stage cooling (Y1), condenser fan relay K10 is ener
gized. 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 contactor K3. K3 immediate
ly switches.
4- When contacts K31 close, the indoor blower is energized immediately and
begins operating. When K32 closes, a circuit is completed to the optional
economizer to open the outdoor air dampers to minimum position.
5- When contacts K101 and K102 close, condenser fans B4 and B5 are ener
gized and immediately begin operating. When contacts K103 closes, a
24VAC circuit is completed through the first stage safety limits to energize
contactor K1. Contactor K1 immediately switches.
6- When contacts K1-1 close, comrpressor B1 is energized and imme
diately begins operating.
7- On a call for increased cooling (Y2), demand is passed through the sec
ond stage safety limits to energize contactor K2. In 208/230 voltage
units only, demand is passed through DL15 which delays the demand
for 30 seconds before passing through the second stage safety limits.
8- When contacts K21 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 K131 close, combustion air blower B6 is energized and
immediately begins operating. When contacts K132 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 be
gins its retrial timing sequence.
15- When blower delay K25 ends its timing period, K251 switches. A
24VAC circuit is completed through K201 to energize blower contac
tor K3.
16- When contacts K31 close, the indoor blower is energized immedi
ately begins operating. When K32 closes, a circuit is completed to
the optional economizer to open the outdoor air dampers to mini
mum position.
17- On a call for increased heating (W2), demand passes through
K202 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 deenergized and blower limit relay K20 is im
mediately energized.
20- When A3 is deenergized, the gas valve (W1) and blower delay (K25)
are both deenergized.
21- When K201 switches, blower contactor K3 is energized to continue blow
er operation during the time that safety limits are open. When K202
opens, second stage thermostat demand is prevented from reaching the
second stage operator of the gas valve (W2).