Installation manual

035-16682-000-E-0303
Unitary Products Group 75
NOTE: The economizer may function, but all mechanical
cooling stages are locked out if LOR1 and LOR2 are
disengaged.
3. When the return air temperature climbs above the
MWUP setpoint, relay HR2 (Morning Warm-up Lockout
Relay) is engaged and relays FR1 and FR2 are disen-
gaged. Contact FR-3 closes to restore SSP2 control, so
that the fan volume is now controlled to maintain the duct
pressure at setpoint. Heating is disabled, the CM-VAV
(Control Module, VAV) and ELM (Economizer Logic
Module) are powered. Contact HR2-1 closes to maintain
DAY COOLING MODE operation while contact HR2-2
opens to disable heating should the return air tempera-
ture fall below the MWUP setpoint. CM-VAV calls for
cooling stages to maintain the discharge air temperature.
4. A call for first stage cooling powers terminal Cool1, A
and signals the optional economizer logic module (ELM)
that cooling is required. When conditions are suitable for
economizer use, ELM powers the coil of staging relays
RY1 and RY2. These relays shift the staging of mechani-
cal cooling as listed in the table below. A call for second
stage cooling powers terminal Cool2, A, third stage pow-
ers Cool3, A and fourth stage powers Cool4, A of CM-
VAV.
The controlling RY1/RY2 contact is indicated in paren-
theses after the controlled device.
For units without an economizer, the compressor opera-
tion corresponds to the Mechanical Cooling Mode listed
above and relays RY1 and RY2 are not installed.
The CM-VAV (Control Module) provides a minimum of 4
minutes between each cooling stage call, a 4 minute
minimum ON time for each cooling stage and a 4 minute
minimum OFF time for each cooling stage. As allowed by
the staging timers, CM-VAV engages an additional stage
of cooling each time the discharge air temperature rises
more than 1°F above the discharge setpoint plus 1/2 the
control band setpoint. As allowed by the staging timers,
CM-VAV disengages a stage of cooling each time the
discharge air falls more than 1°F below the discharge
setpoint minus 1/2 the control band setpoint. When the
supply air reset accessory is installed, the stage ON/OFF
control points move upwards as the setpoint is reset by
either the outside air temperature or the space tempera-
ture.
5. A call for Compressor 1 powers the high pressure safety
switch (HP1), the coil of contactor 6M (condenser fan
#1), and the coil of contactor 7M (contactor, condenser
fan #2) through condenser fan cycling switch PS5 (PS5
disables condenser fan #2 operation based upon the dis-
charge pressure of the Compressor 1). If the system
pressures are within HP1 (high refrigerant pressure) and
LP1 (low refrigerant pressure) switch settings and the
solid state compressor motor protector (Compressor
Module No. 1) is not tripped, contactor 1M is engaged to
start scroll Compressor 1.
6. A call for Compressor 2 powers contactor 2M (contactor,
compressor #2) if HP2, LP2 (high and low refrigerant
pressure) and Compressor Module 2 (compressor motor
protector) contacts are closed.
7. 30 and 40 ton only: A call for Compressor 3 powers the
coils of contactors 8M (contactor, condenser fan #3) and
9M (contactor, condenser fan #4 - 40 ton only). If HP3,
LP3 (high and low refrigerant pressure) and Compressor
Module 3 contacts are closed, power is applied to the
coil of Contactor 3M, which starts compressor 3.
8. 40 Ton Only: A call for Compressor 4 powers the coils of
contactor 4M if HP4, LP4 (high and low refrigerant pres-
sure) and Compressor Module 4 contacts are closed.
9. When the time clock contact made between TC and R is
broken, the unit enters night mode. Contact TCR-1
opens to disable the supply fan, the optional power
exhaust, cooling, heating, and the economizer. The
optional outside air dampers are closed with the optional
inlet guide vanes. Contact TCR-2 closes to power termi-
nal N and enable the field installed night mode thermo-
stat (NSB STAT).
10. When the space temperature falls below the NSB STAT
(Night Setback) heating setpoint, NSB STAT makes con-
tact between terminals N and W1, which powers relay
HR1 (NSB Heat Relay). When the HR1-1 contacts close,
the duct pressure controller is activated, the optional
power exhaust system is activated, power is applied to
the airflow proving switch (APS), and power is applied to
starter 5M to engage the supply fan motor. If the supply
fan operates correctly (proper rotation) the pressure dif-
ference between the heating section and the supply fan
section increases and APS closes to enable heating
operation. Contact HR1-3 closes to engage relays FR1
and FR2. Contact FR1-1 closes to engage the unit heat
(optional) at full capacity. Contact FR1-3 closes (FR1-2
opens) to replace the SSP2 (Switch, Static Pressure -
Duct) damper open signal with a constant 24 VAC signal,
TABLE 41: COOLING STAGE RELAYS
CALL
ECONOMIZER
MODE
MECHANICAL
COOLING MODE
COOL 1 Economizer (N/A)
Compressor 1
(RY1- 2)
COOL 2
Compressor 1
(RY1-3)
Compressor 2
(RY1- 4)
COOL 3
Compressor 2
(RY2-1)
Compressor 3
(RY2- 2, 30 and 40
ton only)
COOL4
Compressor 3
(RY2-3)
Compressor 4
(RY2-4, 40 ton
only)