Installation manual

035-16682-000-E-0303
Unitary Products Group 71
NOTE: The economizer may function, but all mechanical
cooling stages are locked out if LOR1 and LOR2 are
de-energized.
3. A call for Compressor 1 powers the high pressure safety
switch (HP1), the coil of contactor 6M (contactor, con-
denser 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 discharge pressure of Compressor 1). If the
system pressures are within HP1 and LP1 (high and 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.
4. 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.
5. 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.
6. 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.
7. Gas Heat Option, Stage 1: A call for W1 energizes the
WR1 coil, closing contact WR2-1, which engages Igni-
tion Control 1 (IC1-terminal TH) and the coil of BR (Sup-
ply Fan Override Relay) which closes contacts BR-1 to
assure that MR (Supply Fan Motor Relay) is engaged.
Once APS (supply air proving switch) closes to acknowl-
edge 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 pow-
ers 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 ignition 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 electronically lockout after three failed igni-
tion attempts.
When the W1 call is canceled, power is removed from
the coil of BR1 and from IC1 terminals TH and PSW
which directs IC1 to close GV1. As long as APS contin-
ues to prove supply fan airflow, IC1 remains powered
and keeps the L1 to IND contacts closed for 45 seconds
to maintain the operation of Draft Motor 1 for a post-
purge of the heat exchanger.
8. 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, IC1 directs GV1 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.
9. 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
TABLE 40: 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 & 40
ton only)
COOL4
Compressor 3
(RY2-3)
Compressor 4
(RY2-4, 40 ton
only)
Disconnect all power supplies before checking or
servicing the electric heat section.