![background image](http://html1.mh-extra.com/html/carrier/50tc-series/50tc-series_product-data_2561619087.webp)
87
SEQUENCE OF OPERATION
General
The sequence below describes the sequence of operation
for an electro--mechanical unit with and without a factory
installed EconoMi$er
t
IV (called “economizer” in this
sequence). For information regarding a direct digital
controller,
see
the
start--up,
operations,
and
troubleshooting manual for the applicable controller.
Electro--mechanical units with no economizer
Cooling —
When the thermostat calls for cooling, terminals G and Y1
are energized. As a result, the indoor--fan contactor (IFC)
and the compressor contactor (C1) are energized, causing
the indoor--an motor (IFM), compressor #1, and outdoor
fan to start. If the unit has 2 stages of cooling, the
thermostat will additionally energize Y2. The Y2 signal
will energize compressor contactor #2 (C2), causing
compressor #2 to start. Regardless of the number of
stages, the outdoor--fan motor runs continuously while
unit is cooling.
Heating
NOTE
: The 50TC is sold as cooling only. If electric
heaters are required, use only factory--approved electric
heaters. They will operate as described below.
Units have either 1 or 2 stages of electric heat. When the
thermostat calls for heating, power is applied to the W1
terminal at the unit. The unit control will energize the
indoor fan contactor and the first stage of electric heat. On
units with two--stage heating, when additional heating is
required, the second stage of electric heat (if equipped)
will be energized when power is applied at the W2
terminal on the unit.
Electro--mechanical units with an economizer
Cooling —
When free cooling is not available, the compressors will
be controlled by the zone thermostat. When free cooling is
available, the outdoor--air damper is modulated by the
EconoMi$er IV control to provide a 50
_
F (10
_
C) to 55
_
F
(13
_
C) mixed--air temperature into the zone. As the mixed
air temperature fluctuates above 55
_
F (13
_
C) or below
50
_
F (10
_
C) 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 (9
_
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). The
power exhaust fans will be energized and de--energized, if
installed, as the outdoor--air damper opens and closes.
If field--installed accessory CO
2
sensors are connected to
the EconoMi$er IV control, a demand controlled
ventilation strategy will begin to operate. As the CO
2
level in the zone increases above the CO
2
setpoint, the
minimum position of the damper will be increased
proportionally. As the CO
2
level decreases because of the
increase in fresh air, the outdoor--air damper will be
proportionally closed. For EconoMi$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$er IV control, it will
take the damper up to 2 1/2 minutes before it begins to
position itself. After the initial power--up, further changes
in damper position can take up to 30 seconds to initiate.
Damper movement from full closed to full open (or vice
versa) will take between 1 1/2 and 2 1/2 minutes. If free
cooling can be used as determined from the appropriate
changeover command (switch, dry bulb, enthalpy curve,
differential dry bulb, or differential enthalpy), then the
control will modulate the dampers open to maintain the
mixed--air temperature setpoint at 50
_
F (10
_
C) to 55
_
F
(13
_
C). If there is a further demand for cooling (cooling
second stage -- Y2 is energized), then the control will
bring on compressor stage 1 to maintain the mixed--air
temperature setpoint. The EconoMi$er IV damper will be
open at maximum position. EconoMi$er IV operation is
limited to a single compressor.
Heating
The sequence of operation for the heating is the same as
an electromechanical unit with no economizer. The only
difference is how the economizer acts. The economizer
will stay at the Economizer Minimum Position while the
evaporator fan is operating. The outdoor--air damper is
closed when the indoor fan is not operating.
Optional Humidi--MiZer Dehumidification System
Units with the factory--equipped Humidi--MiZer option
are capable of providing multiple modes of improved
dehumidification as a variation of the normal cooling
cycle. The Humidi--MiZer option includes additional
valves in the liquid line and discharge line of each
refrigerant circuit, a small reheat condenser coil
downstream of the evaporator, and Motormaster
variable--speed control of some or all outdoor fans.
Operation of the revised refrigerant circuit for each mode
is described below.
NOTE
: x = refrigerant circuit A, B, or C.
50TC
Summary of Contents for 50TC Series
Page 23: ...23 CURBS WEIGHTS DIMENSIONS CHASSIS 1 C08529 Fig 1 Dimensions 50TC 04 07 50TC ...
Page 25: ...25 CURBS WEIGHTS DIMENSIONS CHASSIS 2 C08531 Fig 6 Dimensions 50TC 08 12 50TC ...
Page 27: ...27 CURBS WEIGHTS DIMENSIONS CHASSIS 3 C08533 Fig 11 Dimensions 50TC 14 50TC ...
Page 84: ...84 C08536 Fig 25 2 Stage Cooling Typical Power Diagram 50TC ...
Page 86: ...86 C08576 Fig 27 2 Stage Typical Wiring Diagram 50TC ...