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5151094-UIM-H-0220
Table 15: Additional Static Resistance
Size (Tons)
CFM
Wet Indoor Coil Economizer
700
0.01
800
0.02
900
0.03
1000
0.04
B36 (3.0)
1100
0.05
1200
0.06
1300
0.07
1400
0.08
1100
0.02
1200
0.03
1300
0.04
1400
0.05
1500
0.06
B48 (4.0)
1600
0.07
1700
0.07
1800
0.08
1900
0.09
2000
0.09
1100
0.02
1200
0.03
1300
0.04
1400
0.05
1500
0.06
B60 (5.0)
1600
0.07
1700
0.07
1800
0.08
1900
0.09
2000
0.09
1. The pressure drop through the economizer is greater for 100% outdoor air than
for 100% return air. If the resistance of the return air duct is less than 0.25 IWG,
the unit delivers less CFM during full economizer operation.
Note: Filter pressure drop based on standard filter media tested at velocities not
to exceed 300 ft/min.
SECTION VI: OPERATION
The following sequences of operation are based on using a single-
stage heat pump thermostat.
COOLING SEQUENCE OF OPERATION
1. When the fan switch on the thermostat is in the ON position, the 24 V
at G bring on the indoor blower motor at the selected airflow. When
the fan switch on the thermostat is in the AUTO position, the blower
operates only when there is a call for cooling or heating by the ther-
mostat.
2. On a call for cooling, the thermostat sends 24 V to Y and O to the
defrost control board. The reversing valve solenoid is energized,
and after the antishort cycle period is complete, contactor coil M is
energized. Power is supplied to the compressor and outdoor fan
motor, and the reversing valve switched to the cooling position.
When the fan switch on the thermostat is in the AUTO position, the
indoor blower motor is energized at the YSPD airflow.
3. When the demand for cooling has been satisfied, the 24-V Y signal
is removed, and the M contactor is de-energized. When the fan
switch on the thermostat is in the ON position, the indoor blower
motor continues to run at GSPD. If the fan switch is in the AUTO
position. the indoor motor ramps down after a 60-s delay.
14
HEATING SEQUENCE OF OPERATION
1. When the fan switch on the thermostat is in the ON position, the
1
Filter/Frame Kit
0.00
0.04
0.01
0.06
0.01
0.08
2. On a call for heating, the thermostat sends 24 V to Y on the defrost
0.01
0.10
0.01
0.13
0.02
0.16
0.03
0.17
0.04
0.18
3. For units equipped with supplementary electric heat, when the heat
0.02
0.04
0.02
0.04
0.02
0.05
0.03
0.05
4. When the heating demand is satisfied, the electric heat is de-ener-
0.04
0.06
0.04
0.07
0.04
0.08
0.04
0.09
0.05
0.10
See Table 14 for more information.
0.05
0.11
DEFROST OPERATION
0.02
0.04
0.02
0.04
The demand defrost control implements a temperature differential
(delta-T) demand defrost algorithm. The heat pump is allowed to oper-
0.02
0.05
ate in the heating mode until the combination of outdoor ambient and
0.03
0.05
outdoor coil temperatures indicate that defrosting is necessary. When
0.04
0.06
coil temperature is below the initiate point for the ambient temperature
0.04
0.07
continuously for 4-1/2 min, the heat pump is put into a defrost cycle.
0.04
0.08
This 4-1/2 min timer eliminates unnecessary defrost cycles caused by
refrigeration surges such as those that occur at the start of a heating
0.04
0.09
cycle.
0.05
0.10
A timed inhibit feature prevents the system from responding to a call for
0.05
0.11
defrost less than 40 min after the initiation of the previous defrost. After
the 40-min inhibit time has expired, temperature conditions must call for
defrost continuously for 4-1/2 min before a defrost cycle is initiated. A
temperature inhibit feature prohibits defrost if the coil temperature is
above 40°F.
A forced-defrost feature puts the system into a defrost period every 6 h
and 4 min of accumulated compressor run-time to recirculate lubricants,
unless the coil temperature is above 40°F and the ambient temperature
is above 50°F. All defrost timing occurs only while the compressor is on.
Defrost curve selection maybe switched to pin 4 if a more aggressive
defrost cycle is necessary.
During the defrost mode, the reversing valve is energized, the outdoor
fan is de-energized, the compressor is energized, and the defrost con-
trol provides a 24-V signal from terminal W out to energize electric heat
stage 1, if the unit is so equipped.
For troubleshooting purposes, the defrost cycle can be manually initi-
ated by shorting the TEST pins together for 5 s while Y is energized.
After removing the short, defrost terminates normally during the TEST
mode.
Table 16: Demand Defrost Selection
24 V at G brings on the indoor blower motor at the GSPD. When the
fan switch on the thermostat is in the AUTO position, the blower
operates when there is a call for heating by the thermostat.
control board. After the anti-short cycle period is complete, the 24-V
signal energizes contactor coil M and power is supplied to the com-
pressor and outdoor fan motor. The reversing valve remains in the
heating position. When the fan switch on the thermostat is in the
AUTO position, the indoor blower is energized at the YSPD.
pump cannot meet the demand, the thermostat W sends 24 V. This
signal is sent through the defrost control terminals W to Wout and
energizes the WSPD. The 24-V signal energizes 1st stage of elec-
tric heat.
gized when the 24-V W signal is removed, and the M contactor is
de-energized when the 24-V Y signal is removed. When the fan
switch on the thermostat is in the ON position, the indoor blower
continues to run. When the fan switch is in the AUTO position, the
indoor blower motor ramps down after a 60-s delay.
Unit
024 — 060
024 — 060
*
For extreme environments as necessary only.
Pin Position
2
4*
Johnson Controls Ducted Systems
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