Installation manual

035-16682-000-E-0303
76 Unitary Products Group
thus forcing the inlet guide vane dampers to fully open.
Contact FR2 makes contact between terminals D1 and
D2 to signal the remote VAV boxes to open. Contacts
HR1-2 opens to disable the CM-VAV and ELM (optional
Economizer Logic Module), so cooling is disabled and
the optional economizer outside air dampers are closed.
This operation is maintained until the space temperature
rises above the NSB STAT heating setpoint or DAY
MODE is engaged.
Gas Heat Option, Stage 1:
A call for heat engages Igni-
tion Control 1 (IC1-terminal TH). Once APS (supply air
proving switch) closes to acknowledge supply airflow,
IC1 is powered. IC1 closes contacts between terminals
L1 and IND to engage Draft Motor 1. The W1 call also
routes to IC1 terminal PSW through PS1 (draft fan air
proving switch) and LS1 (limit switch). Switch PS1 closes
to prove combustion airflow and powers normally closed
switch LS1 which opens only with excessive heat
exchanger temperature. When LS1 and PS1 are closed,
IC1 will attempt ignition. IC1 provides direct spark igni-
tion with flame verification and controls the GV1 gas
valve through manual reset switch RS1 (rollout switch). If
RS1 has tripped, GV1 is locked out and IC1 will electron-
ically lockout after 3 failed ignition attempts.
When the W1 call is canceled, power is removed from
IC1 terminals TH and PSW which directs IC1 to close
GV1. As long as APS continues to prove supply fan air-
flow, IC1 remains powered and keeps the L1 to IND con-
tacts closed for 45 seconds to maintain the operation of
Draft Motor 1 for a post-purge of the heat exchanger.
11. Gas Heat Option, Stage 2:
A call for W2 engages Ignition
Control 2 (IC2-terminal TH). Once APS (supply air prov-
ing switch) closes to acknowledge supply airflow, IC2 is
powered. IC2 closes contacts between terminals L1 and
IND to engage Draft Motor 2. The W2 call also routes to
IC2 terminal PSW through PS2 (draft fan air proving
switch) and LS2 (limit switch). Switch PS2 closes to
prove combustion airflow and powers normally closed
switch LS2 which opens only with excessive heat
exchanger temperature. When LS2 and PS2 are closed,
IC2 will attempt ignition. IC2 provides direct spark igni-
tion with flame verification and controls the GV2 gas
valve through manual reset switch RS2 (rollout switch). If
RS2 has tripped, GV2 is locked out and IC2 will electron-
ically lockout after 3 failed ignition attempts.
When the W2 call is canceled, IC2 directs GV2 to close.
As long as APS continues to prove supply fan airflow,
IC2 remains powered and keeps the L1 to IND contacts
closed for 45 seconds to maintain the operation of Draft
Motor 2 for a post-purge of the heat exchanger.
12. Electric Heat Option: A call for heat engages all stages of
electric heat.
On units with the Electric Heat Option, a call for heat
(W1) will initiate the main blower. The blower will pro-
duce static in the supply and the Air Proving Switch
(APS) contacts will close. The APS will complete the cir-
cuit to the first stage of electric heat. If additional heat is
required, a signal (W2) will energize the second stage of
electric heat. When the call for heat (W2) has been satis-
fied, W3 will be de-energized and de-energize second
stage heat. As the call heat (W1) has been satisfied, W2
will be de-energized and the APS will open disconnect-
ing power to the first stage of electric heat.
All electric heat modules have an auto-reset primary limit
and non-restartable back-up limits. Dirty filters, broken
belts, Fan motor burn-out or running this unit below
6,000 CFM will cause the limit to trip on the auto-reset
primary limit. In addition to the primary limit. Back-up lim-
its may trip under these conditions. The back-up limits
are one-trip devices and will have to be replaced should
they trip.
13. When the space temperature rises above the NSB STAT
cooling setpoint, NSB STAT makes contact between ter-
minals N and Y1, which powers relay CCR (Night Set-up
Cooling Relay). When the CCR-1 contacts close, the
duct pressure controller is activated, the optional power
exhaust system is activated, power is applied to the air-
flow proving switch (APS) and to the coil of starter 5M to
engage the supply fan motor. 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 allow mechanical cooling
operation. Contact CCR-2 closes to engage relay HR2
and power CM-VAV and ELM (optional). The unit oper-
ates as though it were in the DAY COOLING MODE (see
above) until the space temperature falls below the cool-
ing setpoint or DAY MODE is engaged.
14. Duct Pressure Control - Inlet Guide Vane Option: The
duct pressure controls are powered with a call for the
supply fan. Once powered, null pressure switch SSP2
(Switch, Static Pressure - Duct) provides floating point
control of the inlet guide vanes. A contact closure is pro-
vided (COM to HI) whenever the duct pressure exceeds
the adjustable setpoint of SSP2, which applies a 24 VAC
signal to wire 3 of the Inlet guide vane actuator (ACT3,
Open vanes). A contact closure is provided (COM to LO)
whenever the duct pressure falls below the duct pres-
sure setpoint minus the null span adjustment of SSP2,
which powers wire 2 of ACT3 (Close vanes). As long as
Disconnect all power supplies before checking and
or servicing the electric heat section.