Lennox GCS16-823

Page 75
C1 DIAGRAM WITH B41 and A8 DIAGRAMS
Electromechanical Thermostat Connected to GCS16-2553, -2753 or -3003 with 470,000 BTUH Input Heat (Without Economizer)
F-GCS162553470, GCS162753470 or GCS163003470
Operation Sequence: C1 and B41 and A8 Sections (electromechanical thermostat wired to
GCS16)
The GCS162553 and CHA162553 and larger units use two compressors and two independent
cooling circuits. However, each evaporator slab is split circuited effectively placing two evaporators
and two expansion valves on each cooling circuit (four expansion valves per unit).
A pilot relay board is factory installed in all models of this size range. The board is used to reduce
contactor chattering caused by long runs of undersized thermostat wire. The relays on the pilot
relay board have a comparatively smaller inrush than the contactors they serve thereby reducing
the potential for contactor chattering.
All models of this size range use a modular" heating section which may be easily changed in the
factory to larger or smaller BTUH input sizes. Each different heat section is represented by a
unique heating section wiring diagram which mates to the unit diagram as shown on the facing
page (diagram A9). Different wiring diagrams are used to represent the different BTUH input sec
tions. The 470,000 BTUH version is shown here.
The 470,000 BTUH heating section is composed of two identical 235,000 BTUH heat exchang
ers with a unique wiring arrangement.. Each heat exchangers is equipped with a two stage gas
valve. First stage heating is handled by the left gas valve and heat exchanger and second stage
heating is handled by both gas valves and both heat exchangers.
In the 2553, 2753 and 3003 models, the condenser fans operate independently. During
normal operation, one fan operates during first stage demand and both fans operate dur
ing second stage demand.
Power:
1- When the unit disconnect closes, line voltage energizes transformer T1 and the compressor
crankcase heaters. Transformer T1 provides 24VAC power to most unit cooling, heating and
blower controls and thermostat. The crankcase heaters are powered at all times but are selfreg
ulating
2- Transformer T18 provides 24VAC power to the unit contactors
3- Transformer T3 (460V and 575V units) is also energized when power is applied to the
unit.
4- Transformer T10 (units equipped with power exhaust fans) is also energized when power is
applied to the unit.
Cooling Demand:
5- On a call for first stage cooling (Y1), demand is routed through DL8 (30 second on delay, 240
second off delay) and the first stage safety limits to energize pilot relay K66.
6- At the same time, the indoor thermostat energizes the indoor blower circuit (G). Blower demand
energizes pilot relay K46.
7- When K661 closes, a 24VAC circuit is completed to energize contactors K1 and K127. Both
contactors immediately switch. K127 closes to energize K10 and K68.
8- When K461 closes, a 24VAC circuit is completed through blower relays K20 and K25 to ener
gize indoor blower contactor K3 and optional economizer (which opens the outdoor air dampers
to mimimum position).
9- When contacts K31 close, the indoor blower is energized immediately and begins operat
ing. When K32 closes, a circuit is completed to the optional economizer to open the outdoor
air dampers to minimum position.
10- When contacts K101 and K681 close, condenser fan B4 and B5 are energized and im
mediately begin operating.
11- When contacts K1-1 close, comrpressor B1 is energized and immediately begins oper
ating.
12- On a call for increased cooling (Y2), pilot relay K67 is energized after DL9 completes a 30 sec
ond on delay.
13- When K671 closes, a 24VAC circuit is completed through the second stage safety limits to en
ergize contactor K14. K14 immediately switches.
14- When contacts K141 close, compressor B13 is energized and immediately begins operat
ing.
Heating Demand:
15- On a call for first stage heating (W1), pilot relay K77 is energized.
16- When K771 closes, a 24VAC circuit is completed into the heating section to energize combus
tion air blower relay K13.
17- When contacts K131 close, combustion air blower B6 is energized and immediately be
gins operating. When contacts K132 close, the gas valve GV1 is energized.
18- As the combustion air blower approaches full speed, combustion air blower prove switch (S18)
closes.
19- When S18 closes a 24VAC circuit is completed through the heating safety switches to energize
burner ignition control A3.
20- When ignition control A3 determines that ignition can begin, A3 simultaneously sends 24VAC to
both operators of the gas valve (GV1 terminals W1 and W2) and to the indoor blower relay (K56)
and also sends spark to the spark electrode. The gas valve immediately opens and blower relay
K56 is immediately energized. The W1 operator of gas valve (GV1) opens immediately and the
W2 operator opens slowly. This means that the burner starts in lowfire and slowly increases to
highfire.
21- When K561 closes, blower delay relay K25 is energized. K25 begins its timing sequence.
22- When flame is sensed by the ignition control, spark is stopped and the gas valve (GV1) 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.
23- When blower delay K25 ends its timing period, K251 switches. A 24VAC circuit is completed
through K201 to energize blower contactor K3 and optional economizer (which opens the
outdoor air dampers to minimum position).
24- When contacts K31 close, the indoor blower is energized immediately begins operat
ing.
25- On a call for increased heating (W2), pilot relay K49 is energized.
26- When K491 closes, a 24VAC circuit is completed into the heating compartment to ener
gize time delay DL3. DL3 immediately begins its timing sequence.
27- When DL3 time delay has elapsed, DL3 closes internally to complete a circuit to energize the
second stage heat pilot relay K19.
28- When K191 closes, combustion air blower B15 is energized and immediately begins operating.
When contacts K192 close, gas valve (GV3) is enabled. When K193 closes, the second stage
ignition circuit is enabled.
29- As the combustion air blower (B15) approaches full speed, combustion air blower prove switch
(S45) closes.
30- When S45 closes a 24VAC circuit is completed through the heating safety switches to energize
burner ignition control A12.
31- When ignition control A12 determines that ignition can begin, A12 simultaneously sends 24VAC
to both operators of the gas valve (GV3 terminals W1 and W2) and to the indoor blower relay
(K57) and also sends spark to the spark electrode. The gas valve immediately opens and blow
er relay K57 is immediately energized. The W1 operator of gas valve (GV3) opens immediately
and the W2 operator opens slowly. This means that the burner starts in lowfire and slowly in
creases to highfire.
32- When K571 closes, blower delay relay K25 is energized. This is a redundant sfaety circuit
since K25 is already energized by first stage demand.
33- If either heating limit S10 or S21 open during heating operation, both ignition controls are imme
diately deenergized and blower limit relay K20 is immediately energized.
34- When the ignition controls are deenergized, both gas valves and blower relays (K56 and K57)
are both deenergized.
35- When K201 switches, blower contactor K3 is energized to continue blower operation during the
time that safety limits are open.