JOHNSON CONTROLS
160
FORM 150.72-ICOM7
ISSUE DATE: 10/22/2020
SECTION 8 – UNIT OPERATION
ANTI-COINCIDENCE TIMER
This timer is not present on single-system units. Two
timing controls are present in software to ensure com-
pressors within a circuit or between systems, do not
start simultaneously. The anti-coincidence timer en-
sures there is at least a one minute delay between sys-
tem starts on 2-circuit systems. This timer is NOT pro-
grammable. The load timers further ensure that there
is a minimum time between compressor starts within
a system.
EVAPORATOR PUMP CONTROL AND YORK
HYDRO KIT PUMP CONTROL
The evaporator pump dry contacts (XTBC2 – Termi-
nals 23 and 24) are energized when any of the follow-
ing conditions are true:
1. Low Leaving Chilled Liquid Fault
2. Any compressor is running
3. Daily Schedule is ON, Unit Switch is ON and Re-
mote Stop is closed
The pump will not run if the microprocessor panel has
been powered up for less than 30 s or if the pump has
run in the last 30 s to prevent pump motor overheating.
Whenever the option “YORK HYDRO KIT PUMPS =
1” is selected under the OPTIONS key, the pump con-
trol will be as described above. DO NOT SELECT the
option “YORK HYDRO KIT PUMPS = 2” under the
OPTIONS key. If a dual pump option is installed, the
active pump is selected by the selector switch.
EVAPORATOR HEATER CONTROL
The evaporator heater is controlled by ambient air tem-
perature. When the ambient temperature drops below
40°F (4.4°C) the heater is turned ON. When the tem-
perature rises above 45°F (7.2°C) the heater is turned
OFF. An under voltage condition will keep the heater
OFF until full voltage is restored to the system.
PUMPDOWN CONTROL
Each system has a pump-down feature upon shut-off.
Manual pumpdown from the keypad is not possible.
On a non-safety, non-unit switch shutdown, all com-
pressors but one in the system will be shut OFF. The
LLSV will also be turned OFF. The final compressor
will be allowed to run until the suction pressure falls
below the cutout, or for 180 s, whichever comes first.
STANDARD CONDENSER FAN CONTROL
Condenser fan operation must be programmed with
the OPTIONS key under “Fan Control.” Condenser
fan must be selected for Discharge Pressure only. Fan
control by discharge pressure will work according to
the tables on the following pages (see Table 27 on page
162 and Table 28 on page 163). The fan control on
pressure and fan differential off-pressure are program-
mable under the PROGRAM key. Standard fan control
operates down to a temperature of 25°F.
The delay between turning ON and OFF fan stages is
always fixed at 5 s.
When a fan stage is turned ON by pressure, the on pres-
sure for the next stage is increased 20 psig and ramped
back to the programmed on pressure over the next 20 s.
Typically, standard ambient control on pressure should
be programmed at 385 psig with a differential of 125
psig.
When a fan stage is turned OFF (programmed on pres-
sure minus programmed differential), the off pressure
for the next stage is decreased 20 psig and ramped back
to the programmed off pressure minus the differential
over the next 20 s.
Condenser fan locations are shown in Figure 36 on
page 161. Detailed Standard Fan Control operation
is shown in Table 27 on page 162 and Table 28 on
page 163.
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