Operating Sequence - York YCAQ10 Manual

perature, and the unit is running fully loaded. Correct
superheat setting is 10°-12°F (5.5°-6.6°C).
The superheat is the difference between the actual tem-
perature of the returned refrigerant gas entering the com-
pressor and the temperature corresponding to the suc-
tion pressure as shown in a standard pressure/tempera-
ture chart.
Example:
Suction Temperature
Minus Suction Pressure 60 PSIG (413.4 kPg)
Converted to Temperature
Superheat
The suction temperature should be taken 6" before the
compressor service valve, and the suction pressure is
taken at the compressor suction service valve.
Normally, the thermal expansion valve need not be ad-
justed in the field. If, however, an adjustment is to be
made, the expansion valve adjusting screw should be
turned not more than one turn at a time, allowing suffi-
cient time (approximately 15 minutes) between adjust-
ments for the system and the thermal expansion valve
to respond and return to settled operation.
If the unit has been functioning satisfactorily during the
initial operating period, it is ready for continuous opera-
tion.

OPERATING SEQUENCE

(ALSO SEE COMPRESSOR CAPACITY CONTROL)
NOTE: The operating sequence described below relates
to operation after power has been applied on a
hot water start (such as start-up commissioning).
On compressor start-up, internal timers limit mini-
mum time between compressor starts to 1
minute, time between compressor start and load-
ing to 2 min., and time between optional stages
of loading to 2 min. which may make the chiller
initially appear to deviate from normal operation
described on pages 29-30.
1. For the system compressors to run, all Manual Re-
set Cut-outs must be reset, the Flow Switch must be
closed, and any remote cycling contacts must be
closed.
2. As long as power is applied, the Crankcase Heater
will be on and stay on as long as the compressor is
not running.
3. When the System Power Switch is applied, the unit
will start a 2 minute start-up timer.
4. At the end of the 2 minute timer, the 10 minute anti-
recycle timer will start at T = 0. At this time the Micro
Board will check all system conditions. If no safeties
are tripped and cooling demand is present, the com-
pressor will start (unloaded). If a safety is tripped or
YORK INTERNATIONAL
SINGLE CIRCUIT UNITS
no cooling demand is present, the timer will stay at
T = 0 until proper conditions exist. Coincident with
the start of the compressor, the liquid line solenoid
will open after pumpdown to 13 PSI over suction pres-
sure cut-out is completed.
5. T = 4 sec. The motor current of the compressor
must be > 24% FLA and < 115% FLA. Oil pressure
must be ³ 10 PSID (68.9 kPaD). If these conditions
44°F (6.7°C)
are not met, the compressor shuts down.
34°F (1.1°C)
6. T = 30 sec. At this time the oil pressure of the com-
10°F (5.6°C)
pressor must be a minimum of 25 PSID (172.2 kPaD)
and suction pressure must be 80% cutout.
7. T = 2 min. The compressor will load if cooling de-
mand requires.
8. T = 4 min. The compressor's suction pressure must
be ³ cut-out (cut-out = 44 PSIG (303 kPa)). At the
same time, the oil pressure of the compressor must
be ³ 20 PSID (137.8 kPaD).
9. T = 10 min. The anti-recycle timer times out. This
places the timer at T = 0 position. The compressor
will run as long as cooling demand exists.
10. If cooling demand drops and the compressor shuts
down, restart cannot occur until the 10 minute anti-
recycle timer times out and a minimum time of 2 min-
utes passes. This assures a minimum time of 2 min-
utes passes between starts, even if a power failure
occurs. At restart, the 10 minute anti-recycle starts
at T = 0.
11. Crankcase Heater – Any time the compressor stops
the crankcase heater will be energized.
12. Pumpdown – The system is equipped with a pump-
down on start-up routine which eliminates the need
for a recycling pumpdown. On start-up of the com-
pressor, the system will pumpdown to 13 lb. (89.3
kPa) above the suction pressure cut-out before the
liquid line solenoid opens. As a result of this, no
pumpdown mode is included in the system switch.
STANDARD FAN CYCLING
Condenser Fans are cycled by the Micro in response to
outside ambient temperature and Condenser (Dis-
charge) Pressure.
Standard chillers are equipped to operate at ambients
down to 35°F (1.7°C). Below 35°F (1.7°C), a Low Ambi-
ent Kit is required to eliminate nuisance faults (trips).
Fan operation with a Low Ambient Kit is discussed in
the "Options" Section, Page 85. Standard fan operation
and fan placement are shown at the top of page 36.
FORM 150.40-NM25
35