Carrier WEATHERMASTER 50HJQ004-016 Product Data page 164

Controls (cont)
Sequence of operation — 50TFQ004-012 and
50HJQ004-012
Cooling, units without economizer — When thermo-
stat calls for cooling, terminals G and Y1 are energized.
The indoor-fan contactor (IFC), reversing valve solenoid
(RVS1 for sizes 004-007) (RVS1 and RVS2 for
sizes 008-012) and compressor contactor are energized
and indoor-fan motor, compressor, and outdoor fan starts.
The outdoor fan motor runs continuously while unit is
cooling.
Heating, units without economizer — Upon a request
for heating from the space thermostat, terminal W1 will be
energized with 24 v. The IFC, outdoor-fan contactor
(OFC), C1, and C2 will be energized. The indoor fan, out-
door fans, and compressor no. 1, and compressor no. 2
are energized and reversing valves are deenergized and
switch position.
If the space temperature continues to fall while W1 is en-
ergized, W2 will be energized with 24 v, 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 deen-
ergized first, and the electric heater(s) will be deenergized.
Upon a further rise in space temperature, W1 will be
deenergized.
→
Cooling, units with EconoMi$er IV — When free cool-
ing is not available, the compressors will be controlled by
the zone thermostat. When free cooling is available, the
outdoor-air damper is modulated by the EconoMi$er IV
control to provide a 50 to 55 F mixed-air temperature into
the zone. As the mixed-air temperature fluctuates above
55 or below 50 F, 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, then the outdoor-air damper position will be de-
creased to the minimum position. If the mixed-air temper-
ature continues to fall, the outdoor-air damper will close.
Control returns to normal once the mixed-air temperature
rises above 48 F.
If optional power exhaust is installed, as the outdoor-air
damper opens and closes, the power exhaust fans will be
energized and deenergized.
If field-installed accessory CO
the EconoMi$er IV control, a demand controlled ventila-
tion strategy will begin to operate. As the CO
zone increases above the CO
sition of the damper will be increased proportionally. As
the CO level decreases because of the increase in fresh
2
air, the outdoor-air damper will be proportionally closed.
For EconoMi$er IV operation, there must be a thermo-
stat call for the fan (G). If the unit is occupied and the fan is
on, the damper will operate at minimum position. Other-
wise, the damper will be closed.
164
sensors are connected to
2
level in the
2
set point, the minimum po-
2
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$er IV control, it will
take the damper up to 2
sition itself. Any change in damper position will take up to
30 seconds to initiate. Damper movement from full closed
to full open (or vice versa) will take between 1
minutes.
If free cooling can be used as determined from the ap-
propriate changeover command (switch, dry bulb, enthalpy
curve, differential dry bulb, or differential enthalpy), then
the control will modulate the dampers open to maintain
the mixed-air temperature set point at 50 to 55 F.
If there is a further demand for cooling (cooling second
stage — Y2 is energized), then the control will bring on
compressor stage 1 to maintain the mixed-air temperature
set point. The EconoMi$er IV damper will be open at max-
imum position. EconoMi$er IV operation is limited to a
single compressor.
Heating, units with EconoMi$er IV — When the room
temperature calls for heat through terminal W1, the indoor
(evaporator) fan contactor (IFC) and heater contactor no. 1
(HC1) are energized and the reversing valve(s) deenergize
and switches position. On units equipped for 2 stages of
heat, when additional heat is needed, heater contactor no.
2 is energized through W2. The economizer damper
moves to the minimum position. When the thermostat is
satisfied, the damper moves to the fully closed position.
Cooling, units with EconoMi$er2, PremierLink™
control and a thermostat — When free cooling is not
available, the compressors will be controlled by the
PremierLink control in response to the Y1 and Y2 inputs
from the thermostat.
The PremierLink control will use the following informa-
tion to determine if free cooling is available:
• Indoor fan has been on for at least 30 seconds.
• The SPT, SAT, and OAT inputs must have valid
readings.
• OAT must be less than 75 F.
• OAT must be less than SPT.
• Enthalpy must be LOW (may be jumpered if an
enthalpy sensor not available).
• Economizer position is NOT forced.
Pre-cooling occurs when the is no call from the thermo-
stat except G. Pre-cooling is defined as the economizer
modulates to provide 70 F supply air.
When free cooling is available the PremierLink control
will control the compressors, energize the reversing valve(s)
and economizer to provide a supply-air temperature deter-
mined to meet the Y1 and Y2 calls from the thermostat.
If optional power exhaust is installed, as the outdoor-air
damper opens and closes, the power exhaust fans will be
energized and deenergized.
905
1 / minutes before it begins to po-
2
1
/
2
1
and 2 /
2