YORK INTERNATIONAL
82
Sequence of Operation
FORM 100.50-NOM1 (604)
• The Smart Relay continues to keep the Q1 or Q2
contact closed until the pressure switch input to
terminal I4 of the Smart Relay is removed, or for
30 seconds; whichever occurs
Þ
rst.
• The Smart Relay then opens the Q1 or Q2 contact
shutting off the compressor.
REFRIGERANT SAFETY OPERATION
Freezestat Operation
• Freezestat protection only applies if both compres-
sors of the system are energized.
• Both compressors must have been operating for 2
minutes before a lockout can occur.
• The Smart Relay monitors the freezestat input at
terminal I3. If the input is lost, the Smart Relay
turns off the Q2 output and compressor 1B is turned
off.
• The Smart Relay will not close the Q2 contact un-
til 10 minutes has elapsed since the freezestat trip,
provided the freezestat contacts closed during the
10-minute time frame.
Compressor Safety Chain
• Each of the tandem compressor systems has a
compressor safety chain consisting of the following
components. Low Pressure Cutout, High Pressure
Cutout, Compressor Motor Protector, Compressor
Current Overload
• The above safeties are in series and are connected to
the BI1, for system 1; BI 2, for system 2; BI3, for
system 3, inputs to the Primary Unit Controller.
• The Primary Unit Controller monitors the compres-
sor safety chain inputs only when a compressor from
that system is operating.
• When a compressor is started the control shall ig-
nore the compressor safety chain for 30 seconds.
• After the 30 seconds start delay, if the status is not
present for more than one second, the control shall
de-energize all compressors operating in that com-
pressor safety chain.
• The Primary Unit Controller then waits ten minutes
before making the compressors in the tripped sys-
tem available for operation, provided the compres-
sor safety chain has reset.
• Each compressor system shall be assigned two trip
counters, both counters shall start at zero.
• Counter #1 shall:
◦
Increment by 1 any time a trip occurs when either
one or two compressors on the tripped compressor
system are on.
◦
Be reset to zero counts if the compressor system
status input is present for one cumulative hour of
compressor operation following the last compres-
sor safety trip.
◦
Be reset to zero if the power to the Primary Unit
Controller is removed and reestablished.
• Counter #2 shall:
◦
Increment by 1 any time a trip occurs and both
compressors on the system are operating.
◦
Be reset to zero counts if the compressor system
status input is present for one cumulative hour of
compressor operation following the last compres-
sor safety trip.
◦
Be reset to zero if the power to the Primary Unit
Controller is removed and reestablished.
• If the count of either compressor status counter on
a compressor system = 3
◦
The compressors on the system are shut down and
locked out.
◦
A compressor safety lockout fault is declared.
• The power to the Primary Unit Controller must be
removed and reestablished to clear a safety lockout
fault.
FLEXSYS VAV OPERATION
Description of Operation
In the Flexsys mode of operation the unit operates in the
VAV Stand-Alone mode and does not use a thermostat
or space sensor input. See Table 17 for a summary of
the VAV Stand-alone mode of operation. In a Flexsys
system the eco
2
unit supplies condition cool air to a
under
ß
oor delivery system. Compressor operation is
controlled based on the supply air temperature leaving
the evaporator coil. Additional sensors are added to
monitor the temperature of the air off the evaporator coil.
The unit has an opening below the supply air blower
that allows return air to
ß
ow through a bypass duct
and mix with the air off the coil. There is a damper in
the by-pass duct, which modulates to temper the tem-
perature of the mixed air being sent to the under
ß
oor
system. The unit will also accept an analog input from
an under
ß
oor temperature and humidity sensor. These
sensors can be used to monitor the dew point of the air
under the
ß
oor and can reset the SAT temperature if the
air approaches the dew point.