7
Accessories requiring 120 VAC power
sources such as electronic air cleaners
and humidifier transformers may be
powered from the ST9103 EFT. Do not
use the direct drive motor connections as
a power source, since there is a high risk
of damaging the accessories by expo-
sure to high voltage from the auto-
generating windings of the direct drive
motor.
Thermostat wiring connections and air
conditioning contactor low voltage con-
nections are shown in the wiring dia-
grams. Some micro-electronic thermo-
stats require additional controls and wir-
ing. Refer to the thermostat manufac-
turer's instructions.
The thermostat should be located ap-
proximately 5 feet above the floor, on an
inside wall where there is good natural
air circulation, and where the thermostat
will be exposed to average room tem-
peratures. Avoid locations where the
thermostat will be exposed to cold drafts,
heat from nearby lamps and appliances,
exposure to sunlight, heat from inside
wall stacks, etc.
Normal heat anticipator setting: 0.1 A.
For more precise adjustment, the heat
anticipator may be adjusted to the am-
perage draw of the heating control circuit
as measured between the "R" and "W"
terminals of the thermostat. To reduce
the risk of damaging the heat anticipator,
do not measure circuit without first re-
moving one of the two wires first. To
determine the heating circuit amperage
draw:
1. Disconnect one of the “R” or “W”
wires from the thermostat terminal.
2. Connect an ammeter between the
wire and the thermostat terminal to
which it was attached.
3. Note the amperage reading when
the heating contacts are closed.
(System switch must be on “
HEAT
” if
so equipped.
4. Re-connect the thermostat wire. If
the thermostat is serving a combina-
tion heating and air conditioning sys-
tem, pay particular attention to
polarity.
5. When the thermostat is reconnected
and re-plumbed, adjust the heat an-
ticipator setting to match the ob-
served amperage reading.
CIRCULATING AIR BLOWER
All P*HMX and P3LBX furnace models
are equipped with a direct drive blower
system. Direct drive blower speed ad-
justments are not normally required in
properly sized extended plenum duct
systems. The motor RPM and air CFM
delivery will vary automatically to ac-
commodate conditions within the usual
range of external static pressures typical
of residential duct systems. Under-sized
duct systems may require a higher
blower speed to obtain a reasonable
system temperature rise. Some older
duct systems were not designed to pro-
vide static pressure. They typically fea-
ture special reducing fittings at each
branch run and lack block ends on the
trunk ducts. These systems may require
modification to provide some resistance
to the airflow to prevent over- amping of
the direct drive blower motor. Selecting a
lower blower speed may correct this
problem.
Direct drive blower speeds are adjusted
by changing the "hot" wires to the motor
winding connections. Please refer to
wiring diagram in Appendix B or the wir-
ing diagram label affixed to the furnace.
THE NEUTRAL WIRE (normally the
white wire) IS NEVER MOVED TO AD-
JUST THE BLOWER SPEED
.
DO NOT CONNECT POWER LEADS
BETWEEN MOTOR SPEEDS. THE
NEUTRAL WIRE MUST ALWAYS BE
CONNECTED TO THE MOTOR'S DES-
IGNATED NEUTRAL TERMINAL.
It is possible and acceptable to use a
single blower speed for both heating and
cooling modes. The simplest method to
connect the wiring from both modes is to
use a "piggy-back connector" accommo-
dating both wires on a single motor tap.
It is also acceptable to connect the se-
lected motor speed with a pigtail joined
to both heating and cooling speed wires
with a wire nut. As a safety precaution
against accidental disconnection of the
wires by vibration, it is advisable to se-
cure the wire nut and wires with a few
wraps of electricians tape.
If the joining of the blower speed wiring
is done in the furnace junction box, tape
off both ends of the unused wire.
In the heating mode, the circulating fan
start-up is delayed 45 seconds from the
initial call for heat; 30 seconds from the
start of the oil burner.
The circulating fan start-up and shut-
down is immediate in the cooling mode.
The heating mode “fan off” delay may be
field adjusted by manipulating the dip-
switches. See Figures 3.
Fig. 3: Heating “Blower Off” Timings
DISCONNECT THE POWER SUPPLY
TO THE FURNACE BEFORE OPEN-
ING THE BLOWER ACCESS DOOR
TO SERVICE THE AIR FILTER, FAN
AND MOTOR. FAILURE TO SHUT OFF
POWER COULD ALLOW THE
BLOWER TO START UNEXPECT-
EDLY, CREATING A RISK OF DEATH
OR PERSONAL INJURY.
Do not use the blower speed wires as
a source of power to accessories as
electronic air cleaners and humidifier
transformers. The unused motor taps
auto-generate sufficiently high volt-
ages to damage accessory equip-
ment. Use the terminals provided on
the ST9103 EFT
Do not start the burner or blower fan
unless the blower access door is se-
curely in place.
Additional ST9103 Fan Timer Control
information is in Appendix A, Tables, and
in Appendix B, Wiring Diagrams.
Summary of Contents for P2HMX12F08001
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