Johnson Controls Quantech Millennium QCC3080CZE Installation Operation & Maintenance page 129

FORM QCC3-NM1
ISSUE DATE: 12/19/2023
chanical high pressure switch located in the refrigerant
circuit. The system can restart when the discharge pres-
sure drops 40 psig (2.76 barg) below the cutout point.
If the optional discharge pressure transducer is not in-
stalled, this programmable safety would not apply. It
should be noted that every system has a mechanical
high pressure cutout that protects against excessive
high discharge pressure regardless of whether or not
the optional discharge pressure is installed.
S U C T I O N
C U T O U T =
The SUCTION PRESSURE CUTOUT protects the
unit from a coil freeze-up or compressor damage. If
the suction pressure drops below the cutout point, the
system will shut down.
There are some exceptions when the suc-
tion pressure is permitted to temporarily
drop below the cutout point. Details are
explained under the topic of System Safe-
ties.
L O W A M B I E N T
C U T O U T
The LOW AMBIENT TEMP CUTOUT allows the
user to select the unit outside ambient temperature cut-
out point. If the ambient falls below this point, the unit
will shut down. Restart can occur when temperature
rises 2°F (1.11°C) above the cutout setpoint.
A N T I R E C Y C L E
= 6 0 0
The programmable anti-recycle timer ensures that
systems do not cycle. This timer is programmable un-
der the PROGRAM key between 300 - 600 seconds.
Whenever possible, to reduce cycling and motor heat-
ing, the anti-recycle timer should be adjusted as high as
possible. The programmable anti-recycle timer starts
the timer when the first compressor in a system starts.
The timer begins to count down. If all the compressors
in the circuit cycle off, a compressor within the circuit
will not be permitted to start until the anti-recycle timer
Quantech
P R E S S U R E
8 0 . 0 P S I G
T E M P
= 2 5 . 0 ° F
T I M E R
S E C
has timed out. If the lead system has run for less than 5
minutes, 3 times in a row, the anti-recycle timer will be
extended to 10 minutes maximum.
F A N C O N T R O L
P R E S S U R E = X X X P S I G
The Fan Control On-Pressure is the programmed pres-
sure value that is used to stage the condenser fans on,
in relation to discharge pressure. See Condenser fan
control on page 145 in the Section 8: Unit operation
and Tables 27, 28 and 29.
The microprocessor will not allow pro-
gramming the "FAN CONTROL ON
PRESSURE" minus the "FAN CON-
TROL DIFFERENTIAL OFF PRES-
SURE" below 160 psig. This ensures
discharge pressure does not drop too low.
F A N D I F F E R E N T I A L
P R E S S U R E =
The Fan Differential Off Pressure is the programmed
differential pressure value that is used to stage the con-
denser fans off, in relation to discharge pressure. See
Condenser fan control on page 145 in the Section 8:
Unit operation and Tables 27 - 31.
The microprocessor will not allow pro-
gramming the "FAN CONTROL ON
PRESSURE" minus the "FAN CON-
TROL DIFFERENTIAL OFF PRES-
SURE" below 160 psig. This ensures
discharge pressure does not drop too low.
T O T A L N U M B E R
C O M P R E S S O R S
The TOTAL NUMBER OF COMPRESSORS are the
amount of compressors in the unit, and determines the
stages of cooling available. Notice in Table 33 on page
131 that the selection available will vary depending
on the unit model.
This MUST be programmed correctly to
ensure proper condensing unit operation.
SECTION 7: UNIT CONTROLS
O N
O F F
X X X P S I G
O F
= 6
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