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ST9120B,U UNIVERSAL ELECTRONIC FAN TIMERS
Location and Mounting
Mount the ST9120B,U Electronic Fan Timer in the
appliance wiring compartment using the two # 8 1/2-in.
self-tapping screws.
Wiring
CAUTION
Explosion or fire hazard.
When installing the ST9120B,U, carefully check all
appliance wires to make sure they are all
connected to desired terminals at ST9120B,U.
Incorrect wiring can lead to explosion hazard, fire,
or equipment damage.
Make sure that all wiring complies with local codes and
ordinances. Disconnect power before making wiring
connections. Refer to Fig. 1–6 for standard wiring
connections. Refer to Fig. 7–9 for schematic of provided
wiring adapters.
Adjustable DIP Switch
The ST9120B,U control provides a wide variety of
configurable heat on, heat off, cool on and cool off delays.
Set the delay DIP switches as shown in Fig. 10 The heat-
on delay time starts when the main gas valve is energized
at the start of a thermostat call for heat; the heat-off delay
time starts when the main gas valve is deenergized at the
end of a thermostat call for heat. The cool fan-on delay
time starts when the compressor is energized at the start
of a thermostat call for cool. The cool fan-off delay time
starts when the compressor is deenergized at the end of
thermostat call for cool.
Twinning
Twinning mode is used when two ST9120B,U controls
operate in parallel. In this mode blower outputs (heat, cool
and continuous speed) are activated or deactivated at
both controls at the same time. Both ST9120B,U are
synchronized through a communication bridge utilizing
TWIN quick connect terminals, communication hardware
and special software package.
To get into twinning mode both ST9120B,U must share
common 24 VAC ground, both must be supplied off the
same 24 VAC transformer or two identically-phased
transformers and the TWIN terminals must be
interconnected together. One or both ST9120B,U must be
connected to the thermostat.
If two 24 VAC transformers are used (one for each
ST9120B,U) then the transformers must be phased in (24
VAC HOT legs connected to X terminals at each
ST9120B,U unit must be in the same phase relative to the
24 VAC common ground). If the transformers are phased
out the twinning mode will not be achieved.
It is permissible to interconnect just two ST9120B,U to
operate in the twinning mode. The ST9120B,U Twinning
mode is not backwards compatible with legacy Electronic
Fan Timers.
To operate in twinning mode:
1. Interconnect C quick connect terminals at both
twinned ST9120B,U.
2. Interconnect TWIN quick connect terminals at both
twinned ST9120B,U.
69-2252EF—07
3. Use insulate wires of wire gauge at least AWG 24
for the interconnections. Wire lengths shall not
exceed 5 m (15 ft.). Both C and TWIN wires shall
lead in parallel to each other. Keep the wires out of
wires under line voltage, ignition cable and other
sources of electrical noise.
ST9120B,U Wiring Conversion
Instructions
1. Turn off power to appliance. Carefully remove each
wire and connect directly to the corresponding loca-
tion on the new ST9120B,U control board. Be care-
ful to directly connect to the new terminal with the
same labeled identity or label each wire prior to
removing from the original board.
2. Identify the model number of the board being
replaced and set the dip switches based on Table 3.
CAUTION
Explosion Hazard/Fire Hazard
ST9101 wiring harness adapter and ST9141
wiring harness adapter are very similar because
both use identical connectors. Ensure proper
harness is selected for the target system. Using
the wrong wiring harness adapter leads to target
system and/or ST9120B,U control damage.
ST9101 to ST9120B,U Wiring
Conversion Instructions
1. Turn off power to appliance and carefully remove
each wire and connect directly to the new
ST9120B,U control board before removing the
existing control. Use Table 1 to determine the
proper ST9120B,U terminal for each corresponding
ST9101 connection. Connect the wiring in accor-
dance with schematic at Fig. 3. Be careful to directly
connect to the new terminal or label each wire prior
to removal from original board.
CAUTION
Electronic air cleaner use.
If electronic air cleaner is used in systems with
continuous blower speed, connect the electronic
air cleaner to line voltage input L1.
2. Unplug the 9-pin connector and plug existing wiring
harness directly into the 9-pin connector found on
the ST9101 wiring adapter 50011959. See Fig. 7
and Table 4 for further wire harness adapter
description.
3. Plug the 6-pin connector found on the ST9101 wir-
ing adapter directly to the open 6-pin connector on
the new ST9120B,U control board.
4. Take the two remaining white wires on the ST9101
wiring adapter and connect to Neutral quick connect
terminals on the ST9120B,U.
5. Take the black wire on the ST9101 wiring adapter
and connect to the L1 quick connect terminal on the
ST9120B,U.
6. Take the blue wire on the ST9101 wiring adapter
and connect to the IND quick connect terminal on
the ST9120B,U.
7. Identify the model number of the board being
replaced and set the dip switches based on Table 3.
8. Check proper connection using Fig. 3.
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