YORK INTERNATIONAL
55
FORM 150.40-NM25
DUAL CIRCUIT UNITS
2. Flow Switch/Remote Cycling Device: The Micro
Board monitors the closure of the Flow Switch Con-
tacts to assure that water flow is present in the
evaporator. The Micro Board senses the Flow
Switch input to the R.P. Relay whose contacts con-
nect to J19 of the Combo Board. If the Flow Switch
opens, an “A” code will be displayed and both sys-
tems will shut down and will not restart until flow is
present. The Flow Switch is connected to termi-
nals 3 & 4 of the terminal block (TB5) at the lower
left of the Power Panel. See Fig. 34.
Remote EMS/BAS/Time Clock devices are wired
in series with the Flow Switch and can be used to
start and stop the unit. Anytime these contacts open,
an “A” Code will appear on the display indicating a
Flow Switch problem or an EMS/BAS/Time Clock
stop.
OTHER SAFETY CONTROLS
1. Suction Pressure: If SYS 1 Suction Pressure exceeds
105 PSIG (723 kPaG), the Micro Board will not allow
loading or will unload SYS 1 compressor. It will auto-
matically allow reloading of SYS 1 when suction pres-
sure drops below 95 PSIG (654 kPaG). If SYS 2 Suc-
tion Pressure exceeds 95 PSIG (654 kPaG), the Mi-
cro Board will not allow loading or will unload SYS 2
compressor. It will automatically allow reloading of
SYS 2 when suction pressure drops below 85 PSIG
(585 kPaG). Since high suction pressure relates to
high discharge pressure, this feature reduces the
chance of faulting on high discharge pressure by un-
loading or inhibiting loading which reduces the dis-
charge pressure.
2. Discharge Pressure: If SYS 1 Discharge Pressure
exceeds 390 PSIG (2687 kPaG), the Micro Board will
not allow loading or will unload SYS 1 compressor. It
will automatically allow reloading of SYS 1 when suc-
tion pressure drops below 330 PSIG (2274 kPaG). If
SYS 2 Discharge Pressure exceeds 380 PSIG (2618
kPaG), the Micro Board will not allow loading or will
unload SYS 2 compressor. It will automatically allow
reloading of SYS 2 when discharge pressure drops
below 320 PSIG (2205 kPaG). This feature reduces
the chance of faulting on high discharge pressure by
unloading or inhibiting loading which reduces the dis-
charge pressure.
3. Lead System Fault Override: Whenever the lead sys-
tem faults, the Micro automatically switches the lag
system to the lead in an effort to keep chilled water
temperature nearer to setpoint.
ANTI RECYCLE TIMER
Any time a compressor shuts down for any reason, re-
start cannot occur until the 10-minute anti-recycle timer
has timed out (Timer starts with Compressor start) and
a minimum of 2 minutes (2-minute start-up timer) has
expired since compressor shutdown.
Ex. Anti-recycle timer has 8 min. left at shutdown:
Restart can occur in 8 minutes (Anti-recycle time
greater than 2 min.)
Ex. Anti-recycle timer has 1 min. Ieft at shutdown:
Restart can occur in 2 min. (Anti-recycle time less
than 2 min.)
Ex. Anti-recycle timer has timed out at shutdown:
Restart can occur in 2 min. (Anti-recycle time less
than 2 min.)
Ex. Power failure has occurred: Restart can occur
2 min. after the return of power (Anti-recycle time
less than 2 min.)
Both compressors can never start simultaneously un-
der any condition. A one minute time delay will always
separate compressor starts.
EMS/BAS/TIME CLOCK CONTROLS
REMOTE START/STOP BY A TIME CLOCK,
BUILDING AUTOMATION, OR ENERGY
MANAGEMENT SYSTEM
Remote starting and stopping is accomplished by open-
ing and closing dry contacts, controlled by a remote
source, connected to the R.P. Relay. These contacts will
be wired in series with the Flow Switch which is con-
nected to terminals 3 & 4 of the terminal block (TB5) at
the lower left of the Power Panel. (See Fig. 34.) The
Micro Logic Board looks for the closure of the contacts
as a signal to start the system. Opening the contacts is
a signal to stop the system.
Since the remote contacts are wired in series with the
Flow Switch, an “A” code will appear on the display when
a REMOTE STOP command is given (contacts open).
If an Optional Digital Input Board is installed, Remote
START/STOP can be accomplished by connecting “dry”
contacts between terminals 71 & 72 of TB8 on the lower
left of the power panel. Opening the contacts stops the
compressors and displays an “A” code. Closing the con-
tacts allows starting the compressors and extinguishes
the “A’’ code. See Fig. 50 and 51 to properly configure
the switches on the Micro Logic Board (SW4; ON) to
make this option active. If this function is not used, ter-
minals 71 & 72 on TB8 must be jumpered or an “A”
code will result and the compressors will not run. See
EMS/BAS Option in “OPTIONS” Section for more in-
formation.
