Sequence Of Operation; Cooling, Unit Without Economizer; Cooling, Unit With Economi$Er Iv; Heating, Unit Without Economizer - Carrier WeatherMaker 50TCQ Product Data

Cooling, unit without economizer

When thermostat calls for cooling, terminals G and Y1 are
energized. The indoor fan contactor (IFC), reversing valve
solenoid (RVS) and compressor contactor are energized
and indoor fan motor, compressor, and outdoor fan starts.
The outdoor fan motor runs continuously while unit is
cooling.
Two-stage models: If Stage 1 cooling does not satisfy the
space load, the space temperature will rise until
thermostat calls for Stage 2 cooling (Y2 closes). Defrost
Board activates Stage 2 Compressor. Reversing valve 2
switches to Cooling position. Compressor 2 contactor is
energized; Compressor 2 starts and Circuit 2 operates in
Cooling mode.
When Cooling Stage 2 is satisfied, thermostat Y2 opens.
Compressor 2 contactor is de-energized; Compressor 2
stops. Reversing Valve 2 remains energized.
When Cooling Stage 1 is satisfied, thermostat Y1 opens.
Compressor 1 contactor is de-energized; Compressor 1
stops. Outdoor fan relay is de-energized; outdoor fans
stop. After the Fan Delay period, the Indoor fan contactor
is de-energized; indoor fan stops (unless Continuous Fan
operation has been selected). Reversing Valve 1 remains
energized.
Reversing valve solenoids are energized in Cooling
modes. Each solenoid will remain energized until the next
Heating mode is initiated for this circuit.

Heating, unit without economizer

Upon a request for heating from the space thermostat,
terminal W1 will be energized with 24V. The IFC,
outdoor fan contactor (OFC), C1, and C2 will be
energized. The indoor fan, outdoor fans, and compressor
no. 1, and compressor no. 2 are energized and reversing
valves are de- - energized and switch position.
If the space temperature continues to fall while W1 is
energized, W2 will be energized with 24V, and the heater
contactor(s) (HC) will be energized, which will energize
the electric heater(s).
When the space thermostat is satisfied, W2 will be
de- - energized first, and the electric heater(s) will be
de- - energized.
Upon a further rise in space temperature, W1 will be
de- - energized.
Two compressor models: When the thermostat calls for
heating, terminal W1 is energized. Defrost Board
de-energizes both reversing valve solenoids and reversing
valves move to Heating position. The indoor fan contactor
is energized; indoor fan motor starts. Outdoor fan relay is
energized; both outdoor fan motors run. Compressor
contactors C1 and C2 are energized; both refrigeration
circuits operate in Heating mode.
If Stage 1 heating does not satisfy the space load, the
space temperature will fall until thermostat calls for Stage

SEQUENCE OF OPERATION

2 heating (W2 closes). Terminal W2 is energized. Defrost
Board issues an output at EHEAT. Heater contactor 1 and
heater contactor 2 (if installed) are energized; all electric
heaters are energized.
When space heating load is partially satisfied, thermostat
terminal W2 is de-energized; heater contactors are
de-energized and all electric heat is terminated. Stage 1
heating continues.
When the space heating load is fully satisfied, thermostat
terminal W1 is also de-energized.
Reversing valve solenoids remain de-energized until the
next call for Cooling mode is initiated.

Cooling, unit with EconoMi$er IV

When free cooling is not available, the compressors will
be controlled by the zone thermostat. When free cooling is
available, the outdoor air damper is modulated by the
EconoMi$er IV control to provide a 50 to 55_F (10_ to
13_C) mixed air temperature into the zone. As the mixed
air temperature fluctuates above 55 or below 50_F (13_ to
10_C), the dampers will be modulated (open or close) to
bring the mixed air temperature back within control.
If mechanical cooling is utilized with free cooling, the
outdoor air damper will maintain its current position at the
time the compressor is started. If the increase in cooling
capacity causes the mixed air temperature to drop below
45_F (7_C), then the outdoor air damper position will be
decreased to the minimum position. If the mixed air
temperature continues to fall, the outdoor air damper will
close. Control returns to normal once the mixed air
temperature rises above 48_F (9_C).
If optional power exhaust is installed, as the outdoor air
damper opens and closes, the power exhaust fans will be
energized and de- - energized.
If field- - installed accessory CO
the EconoMi$er IV control, a demand controlled
ventilation strategy will begin to operate. As the CO
level in the zone increases above the CO
minimum position of the damper will be increased
proportionally. As the CO
increase in fresh air, the outdoor air damper will be
proportionally closed.
For EconoMi$er IV operation, there must be a thermostat
call for the fan (G). If the unit is occupied and the fan is
on, the damper will operate at minimum position.
Otherwise, the damper will be closed.
When the EconoMi$er IV control is in the occupied mode
and a call for cooling exists (Y1 on the thermostat), the
control will first check for indoor fan operation. If the fan
is not on, then cooling will not be activated. If the fan is
on, then the control will open the EconoMi$er IV damper
to the minimum position.
On the initial power to the EconoMi$er IV control, it will
take the damper up to 2
position itself. Any change in damper position will take
93
sensors are connected to
2
setpoint, the
2
level decreases because of the
2
1
/ minutes before it begins to
2
2