68
YORK INTERNATIONAL
Kit is not required if Discharge Pressure Transducers
are installed.
When the Low Ambient Option is installed, the follow-
ing physical changes are made to the standard chiller:
1.
Discharge pressure transducers and wiring are
added.
2.
Reversing contactors 7M with supporting wiring
is added.
3.
A second Relay Output Board and wiring is in-
stalled.
Programming
The control panel may be programmed for “AMBIENT
& DISCH PR FAN CONTROL” (Ambient & discharge
pressure fan control) or by “DISCHARGE PRESSURE
FAN CONTROL” (Fan control by discharge pressure
only). This is selected by placing SW. 8 on the Micro-
processor to the appropriate position. See page 31.
SW. 2 on the Microprocessor Board must also be pro-
grammed for “LOW AMBIENT CONTROL” to allow op-
eration at temperatures below 25°F. To accomplish this,
place SW. 2 in the CLOSED position. See page 30.
After the switch is properly positioned, the OUTSIDE
AIR TMP LOW CUT-OUT in the PROGRAM mode can
then be programmed between 0° - 25°F. See page 36.
NOTE: For operation below 0°F, program the cut-out
for 0°F. This will cause the microprocessor to
ignore the low ambeint cut-out regardless of
temperature.
Operation of the fans will be discussed in both “Ambi-
ent and Pressure Control” as well as “Pressure Only”
control in the followintg text.
Ambient and Pressure Fan Control
0°F - 25°F
Fan operation below 25°F is controlled only by the dis-
charge pressure. Controlling action by the fans may be
by either system. 4 steps of fan control operate as
follows:
1.
Until discharge pressure reaches 320 PSIG, the
fans will be completely off.
2.
The second stage of fan control will energize fan
1 (7M) in the reverse direction when the discharge
pressure exceeds 320 PSIG. Once the reversing
contactors are energized, they will stay on until
the discharge pressure of the system falls below
120 PSIG, the ambient temperature exceeds 35°F,
or discharge pressure of the system rises above
340 PSIG.
NOTE: The corresponding compressor must be on for
minimum of 4 sec. before the reversing fans
are permitted to start.
3.
The third stage of fan control will energize fan 2
(6M) as well as turn off the reversing fan 1 when-
ever discharge pressure of either system exceeds
340 PSIG. This fan will stay on until discharge
pressure drops below 120 PSIG.
NOTE: The corresponding compressor must be on for
4 sec. before these fans are permitted to start.
4.
The fourth stage of fan control will energize fan 1
(5M) in the forward direction whenever discharge
pressure of either system exceeds 360 PSIG. This
fan will stay on until discharge pressure of either
system drops below 140 PSIG.
NOTE: The corresponding compressor must be on for
4 sec. before this fan is permitted to start. Fan
2 will also be operating.
Ambient and Pressure Fan Control
25° - 45°F
Fan control between 25°and 35°F is controlled by dis-
charge pressure. If the reversing fan is on, the revers-
ing fan will continue to operate until the temperature
reaches 35°F or discharge pressure reaches 340 PSIG.
At 35°F or 340 PSIG, fan 2 (6M) will energize. Between
25°F and 45°F if the reversing fan is not operating,
after 4 seconds of compressor operation fan 2 (6M)
will energize. This is identical to standard fan control
by temperature (page 59). No pressure override ex-
ists. If temperature drops below 25°F, this fan will re-
main on until cycled off by discharge pressure of ei-
ther system dropping below 120 PSIG.
Ambient and Pressure Fan Control
45°F and Higher
Fan control above 45°F is strictly controlled by tem-
perature with no pressure override.
After 4 seconds of operation, fan 2 (6M) will energize
turning the fan in the forward direction.
After 30 seconds of operation, fan 1 (5M) will energize
turning an additional fan on in the forward direction.
This is identical to standard fan control by temperature
(page 59). This fan will de-energize if ambient tem-
perature drops below 40°F.
