Johnson Controls Quantech Millennium QCC3080CZE Installation Operation & Maintenance page 107

FORM QCC3-NM1
ISSUE DATE: 12/19/2023
Form QCC3-CL2
Issue date: 11/10/2023
4. Put the unit into service mode and cycle each con-
denser fan to ensure correct rotation. Refer to Form
QCC3-NM1, Service and Troubleshooting section
for more information. ................................................
5. Before this step, turn system 2 off (if applicable – re-
fer to QCC3 - Installation, Operation, Maintenance
Manual (Form QCC3-NM1) Unit Keys, Option 2 for
more information on system switches). Connect a
manifold gauge to system 1 suction and discharge
service valves. ........................................................
Turn on the control panel unit switch. As each
compressor cycles on, ensure that the discharge
pressure rises and the suction pressure de-
creases. If this does not occur, the compressor
being tested is operating in the reverse direc-
tion and must be corrected. After verifying cor-
rect compressor rotation, turn off the unit switch.
The discharge air or suction pressure
setpoint may need to be temporarily
lowered to ensure all compressors cycle
"on."
This unit uses scroll compressors
which can only operate in one direc-
tion. Failure to observe this will lead
to compressor failure.
6. Turn system 1 off and system 2 on (refer to QCC3 -
Installation, Operation, Maintenance Manual (Form
QCC3-NM1) Unit Keys, Option 2 for more informa-
tion on system switches). ........................................
Turn on the control panel unit switch. As each com-
pressor cycles on, ensure that the discharge pres-
sure rises and the suction pressure decreases. If
this does not occur, the compressor being tested
is operating in the reverse direction and must be
corrected. After verifying the correct compressor
rotation, turn off the unit switch.
The chilled liquid setpoint may need
to be temporarily lowered to ensure
all compressors cycle "ON".
Quantech
Quantech
D. CHECKING SUPERHEAT AND SUBCOOLING
The subcooling temperature of each system can be calcu-
lated by recording the temperature of the liquid line at the
outlet of the condenser and subtracting it from the liquid line
saturation temperature at the liquid stop valve (liquid line
saturation temperature is converted from a temperature/
pressure chart).
Example:
Liquid line press. =
202 psig converted to temp.
minus liquid line temp.
Subcooling =
The subcooling should be adjusted to 15°F at design
conditions.
Record the liquid line pressure and its corresponding tem-
perature, liquid line temperature and subcooling below:
SYS 1
Liquid line press. = _______
Saturated temp. = _______
Liquid line temp. = _______
Subcooling = _______
After the subcooling is verified, the suction superheat
should be checked. The superheat should be checked only
after steady state operation of the condensing unit has been
established, the leaving water temperature has been pulled
down to the required leaving water temperature, and the
unit is running in a fully loaded condition. Correct superheat
setting for a system is 10°F - 15°F (5.56°C - 8.33°C) 18 in.
(46 cm) from the cooler.
Superheat should typically be set for no less than 10°F with
only a single compressor running on a circuit. The super-
heat is calculated as the difference between the actual tem-
perature of the returned refrigerant gas in the suction line
entering the compressor and the temperature corresponding
to the suction pressure as shown in a standard pressure/
temperature chart.
Example:
Suction temp. =
minus Suction press.
60 psig converted to temp. - 34°F
Superheat =
When adjusting the expansion valve (TXV only), the adjust-
ing screw should be turned not more than one turn at a
time, allowing sufficient time (approximately 15 minutes)
between adjustments for the system and the thermal expan-
sion valve to respond and stabilize.
Ensure that superheat is set at a minimum of 10°F (5.56°C)
with a single compressor running on each circuit.
SECTION 6: COMMISSIONING
102°F
- 84°F
18°F
SYS 2
_______ psig
_______ °F
_______ °F
_______ °F
46°F
12°F
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