Lennox Harmony III Installation Instructions Manual page 24

Gas Heating Checkout − Central Control − Dual Fuel Option and BPS
Prerequisites:
S
Central mode switch on
S
Red LED on the central mode fan switch on
S
Zone 1 thermostat set to Heat
S
Balance Point Sensor set at higher temperature than
outdoor BPS-sensed temperature
central mode On
DAMPER 2,3,4 OFF
Discharge Probe Checkout (All Systems)
The discharge air sensor is a temperature-dependent re-
sistor; the higher the temperature, the lower the resist-
ance. To confirm the sensor is functioning, disconnect both
sensor leads from the circuit board. Using a digital voltme-
ter (DVM) set to read resistance, touch the leads from the
sensor to the probes of the DVM.
Do not touch both probes with your fingers doing so will
produce a faulty reading. At 77°F, the resistance of the
sensor will be 10K ohm; at lower probe temperatures, ex-
pect higher resistance; at warmer probe temperatures, ex-
pect lower resistance.
After reading the resistance at room temperature, warm
the tip of the sensor by holding it in the palm of your hand,
and take another resistance reading. This reading should
be noticeably lower than the room temperature reading.
The zone control system will monitor the operation of the
probe and determine if a failure has occurred. The probe is
an integral (but replaceable) part of the zone control sys-
tem. The zone control system will indicate if the probe is
operating improperly and needs to be replaced.
The discharge air temperature probe serves several pur-
poses:
1. In cooling systems (and heat pump systems in cooling
mode) the probe varies the speed of the compressor
505023M 04/06
(W) RED on
W1 on
fan on hEATING on
OUTPUT STATUS LEDs
1. Set zone 1 thermostat for a heat demand; check:
Zone 1 thermostat W LED on (heating demand).
D
Output Heat W1 LED on (furnace on).
D
D Heating LED on.
All damper LEDs off (damper open).
D
2. The furnace will begin its ignition sequence after Zone
1 has demanded heat. The zone control system will
start the furnace blower on low speed (0 PIAB air) 45
seconds after the combustion cycle has begun.
3. When warm air is sensed by the discharge air sensor,
the fan LED will light and the blower will slowly in-
crease to speed. The blower will operate at a speed
equivalent to the PIAB calculated for all zones calling,
taking into account the heating air reduction jumper
position. It may take the blower 60 to 90 seconds to
reach this speed.
4. Remove the heat demand from zone 1 (no heat input
or output and no blower demand). Upon removal of the
demand from zone 1, check:
D Zone 1 thermostat W LED off (no heat demand).
Output Heat W1 LED off.
D
Fan LED off.
D
Heating LED off.
D
After 3−1/2 minute purge time, furnace blower turns off.
from high to low to off in order to maintain a constant
discharge air temperature and prevent coil freezing.
2. In gas heating systems, it is responsible for increasing
the speed of the blower to the setting of the CFM jump-
ers after the heat exchanger has warmed up to about
100_F. Also stages equipment up and down to control
discharge air temperature.
3. In heat pump systems operating in the heating mode,
the probe varies compressor speed and stages of aux-
iliary heat in order to maintain a constant discharge air
temperature.
Pressure Switch Checkout (Heat Pump Sys-
tems Only)
The high pressure switch is a normally closed (N.C.) auto-
reset high pressure switch located in the compressor dis-
charge line or on the suction valve service port. The R−22
switch is factory set to open when operating pressures rise
above 375 psig and closes when the pressure drops below
275 psig. The R−410A switch opens at 550 psig and closes
at 425 psig. The intent of the switch is to protect the outdoor
unit from abnormally high operating pressures during mild
weather heating days.
1. Connect refrigerant gauges to the outdoor unit vapor
line.
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