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SGH/SCH036, 060, 120, 240
B-Compressor Controls
1- Crankcase Heater (HR1, HR2, HR5, HR11)
The compressor contains a belly band compressor oil
heater which must be on 24 hours before running
compressors. Energize by setting thermostat so that
there is no cooling demand, to prevent compressor
from cycling and apply power to unit.
2- Low Ambient Pr. Switch (S11, S84, S85, S94)
Switches are installed in the liquid line. Switches
maintain adequate discharge pressure by
de-energizing condenser fan(s) when liquid pressure
falls below 240 psig +10 (1655 kPa+69). Switches
close to energize condenser fan(s) when pressure rises
to 450 psig +10 (3 69).
3- Outdoor Fan Relays (K10, K68, K149, K150, K152, K153)
Relays de-energize outdoor fan when temperature
drops below 55°F.
Low Ambient Cycling (see figure 29):
3 & 5 Ton Units—
S11 cycles both variable speed fans
between off and extra low (25% of full speed).
10 Ton Units—
Both condenser fans are energized on a
Y1 cooling demand and continue to operate when Y2
demand is initiated. The M3 (A55) Unit Controller
de-energizes condenser fan 1 when the outdoor
temperature drops below 55°F (13°C). Condenser fan 2
is cycled by S11 and S84 pressure switches (via K68).
Normal operation will resume above 58°F (15°C).
20 Ton Units—
Condenser fans 1, 2 and 3 are
energized on a Y1 cooling demand. An increased Y2
demand will energize condenser fans 4, 5 and 6.
Condenser fan 1 and 6 are de-energized below 40°F
(4.4°C) by M2 (A55) controller and C2 A59
controllers respectively. Condenser fans 2 and 5 are
de-energized below 55°F (13°C) by A55 Unit
Controller and C2 (A178) Compressor 3 & 4
Controller respectively. Condenser fan 3 is
de-energized when
BOTH
S11 and S84 open due to
low pressure. Condenser fan 4 is de-energized when
BOTH
S85 and S94 open due to low pressure.
4- Freezestats (S49, S50, S53, S95)
Switches de-energize compressors when evaporator
coil temperature falls below 29°F (-2°C) to prevent
evaporator freeze-up. Switches reset when evaporator
coil temperature reaches 58°F (15°C).
5- Crankcase Heater Thermostat (S40, S162)
Switches de-energize crankcase heaters when
discharge temperature rises above 94°F+5
(34.4°C+5). Switch opens to energize crankcase
heaters when discharge temperature drops below
74°F+5 (23.2°C+5).
CONDENSER FAN LOCATION
FIGURE 29
COMPRESSORS
EVAP.
UNIT FRONT
EVAP.
COMPR.
UNIT FRONT
1
4
2
5
2
1
10-TON
20-TON
EVAP.
COMPR.
UNIT FRONT
2
1
3 &
5-TON
3
6
Gas Heat Start-Up
FOR YOUR SAFETY READ BEFORE LIGHTING
BEFORE LIGHTING smell all around the furnace area for
gas. Be sure to smell next to the floor because some gas is
heavier than air and will settle on the floor.
Use only your hand to move the gas valve lever. Never use
tools. If the lever will not move, do not try to repair it, call a
qualified service technician. Force or attempted repair may
result in a fire or explosion.
This unit is equipped with an automatic spark ignition system.
There is no pilot. In case of a safety shutdown, move
thermostat switch to
OFF
and return the thermostat switch to
HEAT
to reset ignition control.
WARNING
Electric shock hazard.
Can cause injury or death.
Before attempting to perform any
service or maintenance, turn the
electrical power to unit OFF at
disconnect switch(es). Unit may have
multiple power supplies.
WARNING
Danger of explosion.
Can cause injury or death.
Do not attempt to light manually. Unit
has a direct spark ignition system.
