Installation manual

035-16682-000-E-0303
70 Unitary Products Group
THERMOSTAT SEQUENCE
The thermostat operates in one of three modes: Occupied,
Unoccupied, and Recovery (Warm-up / Cool-down). The pro-
grammable thermostat allows two independent occupied /
unoccupied schedules for each day of the week. In addition
to the programmed schedule, the thermostat keyboard allows
a single key press to provide a 3 hour schedule override into
the occupied mode or a continuous (until key is pressed
again) override into the unoccupied mode.
When unit power interruption occurs, the thermostat provides
a fixed one minute delay before the supply fan will engage
immediately. A four minute delay before the first heating
stage may engage, and a four minute delay before the first
cooling stage may engage. The thermostat maintains a mini-
mum two minute run time for each heating stage and a two
minute minimum off time between successive heating calls.
The thermostat similarly maintains a four minute run time for
each cooling stage and a minimum four minute off time
between successive cooling calls. The thermostat will not
simultaneously call for both cooling and heating stages.
The supply fan operates continuously in the OCCUPIED
and
RECOVERY
modes. An auxiliary economizer contact closes
to enable the economizer control (ELM) when the supply fan
is engaged during the occupied mode. The thermostat cycles
cooling / heating to maintain the space temperature to the
occupied setpoints.
In the UNOCCUPIED MODE
, the supply fan operates only
with cooling / heating calls. The auxiliary economizer contact
is always open and the economizer is disabled during the
unoccupied mode except when free cooling may be used to
condition the space. Cooling / heating stages are cycled to
maintain the space temperature to the unoccupied setpoints.
The RECOVERY MODE
is a special unoccupied mode which
allows transition to occupied mode. The supply fan operates
continuously and the economizer remains disabled. Instead
of maintaining the unoccupied setpoints, the thermostat
ramps the space temperature toward the occupied setpoints.
Cooling stages (Cool-down) or heating stages (Warm-up) are
cycled to slowly ramp the space temperature to the occupied
setpoints. The thermostat uses a built in algorithm to deter-
mine the appropriate time to start space recovery based upon
the deviation from the occupied setpoints and the rate of tem-
perature change.
UNIT CONTROLS SEQUENCE
The thermostat gives a call for heating or cooling, and this is
acted upon by unit controls according to the sequence out-
lined below. Abbreviations for various components corre-
spond to the labels on the wiring diagram.
1. On a call for the supply fan, terminal G powers the coil of
MR (Supply Fan Motor Relay). When the MR-1 contacts
close, the optional power exhaust system is activated,
power is applied to the airflow proving switch (APS), and
power is applied to the overload relay connected to
starter 5M (Supply Fan Motor Starter). If the overload
relay has not tripped, starter 5M closes and the supply
fan motor is engaged. If the supply fan operates correctly
(proper rotation) the pressure difference between the
heating section and the supply fan section increases and
APS closes to enable heating operation, power the auxil-
iary economizer relay, and the cooling lockout control.
For units without optional head pressure control: If the
outside air temperature rises above 50°F, cooling lockout
switch 1 (CLO1) applies power to the coils of LOR1 and
LOR2 (Low Ambient Cooling Lockout Relays) to enable
all mechanical cooling stages by closing contacts LOR1-
1, LOR1-2, LOR2-1, and LOR2-2. If the outside air tem-
perature falls below 40°F, mechanical cooling stages are
locked out.
For units with head pressure control: Cooling lockout
switch 1 (CLO1) applies power to the coil of LOR2 (Low
Ambient Cooling Lockout Relay) to enable third and
fourth (40 ton only) stage mechanical cooling by closing
contacts LOR2-1 and LOR2-2 when the ambient temper-
ature rises above 50°F. If the outside air temperature
falls below 40°F, mechanical cooling stages 3 and 4 (40
ton only) are locked out. Cooling lockout switch 2 (CLO2)
applies power to the coil of LOR1 to enable first and sec-
ond stage mechanical cooling by closing contacts LOR1-
1 and LOR1-2 when the ambient temperature rises
above 10°F. If the outside air temperature falls below
0°F, all mechanical cooling stages are locked out.
On units with optional heating, relay BR (Supply Fan
Override Relay) is wired in parallel with terminal G on
TB12, so that any call for heating engages the coil of
MR. Operation of heating is still dependent upon the
APS closure as described in the preceding paragraph.
2. A call for first stage cooling, Y1 powers the coil of CR1
(first stage cooling relay) signals the optional economizer
logic module (ELM) that there is a call for cooling. On
units with the optional economizer, ELM is also powered
through the economizer auxiliary relay before becoming
active. When conditions are suitable for economizer use,
ELM powers the coil of staging relays RY1 and RY2
(Cooling Stage Control Relays). These relays shift the
staging of mechanical cooling as listed in the table
below. A call for second stage cooling powers terminal
Y2, third stage powers Y3 and fourth stage powers Y4 of
the coil on CR2, CR3, and CR4.
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 RY1 and RY2 are not installed.