Heating Components; Ignitor; Flame Sensor; Harmony Iii - Lennox G71MPP SERIES Unit Information

Harmony IIIt
When the G71MPP is installed in Harmony III applications,
the Harmony III signal is connected to the DS terminals on
the integrated control (figure 4). In this application dip
switch one and dip switch two (which configures to various
thermostats), is overridden. The discharge air temperature
(if used) is also ignored. In order for proper operation on
board jumper W914 must be clipped.
The PWM signal (70−90 Hz with a 3−97% duty cycle) con-
trols the indoor blower motor linearly between the minimum
(shown in table 28) and the maximum CFM set by COOL-
ING dip switches eight through 13. (3% duty cycle = MIN,
97% duty cycle = MAX).
TABLE 28
Minimum CFM
Cool Speed
High
Medium−High
Medium−Low
Low
If there is a W1 heat call while the indoor blower is con-
trolled by Harmony III PWM signal, the integrated control
will after a successful ignition sequence and stabilization
period, modulate the correct firing rate.
Note − All on / off heating and cooling indoor blower
delays are still present with Harmony III.
PWM signal is present at all times with a default value of 3%
duty cycle. Upon the need for a higher duty cycle (more
CFM), the duty cycle will step up at a rate of 1% per second.
Upon a need for less duty cycle, (less or no CFM) the duty
cycle will immediately step down to the demanded % or de-
fault 3% (off).
Along with the PWM signal is a 24VAC Enable signal that is
connected on the integrated control terminal G". The inte-
grated control will not obey the PWM signal unless the en-
able signal is present.
1/2HP 1HP
250 450
250 450
250 450
250 450
C−Heating Components

1. Ignitor

The ignitor is made of durable silicon nitride. Ignitor longev-
ity is enhanced by controlling voltage to the ignitor. The
®
SureLight control provides a regulated 95 volts to the igni-
tor for consistent ignition and long ignitor life. Ohm value
should be 25 to 47. See figure 12 for ignitor location.

2. Flame Sensor

A flame sensor is located on the left side of the burner sup-
port. See figure 11. The sensor is mounted on the flame rol-
lout plate and the tip protrudes into the flame envelope of
the left−most burner. The sensor can be removed for ser-
vice without removing any part of the burners. During op-
eration, flame is sensed by current passed through the
flame and sensing electrode. The SureLight control allows
the gas valve to remain open as long as flame signal is
sensed. To check flame sense signal use the push−button
found on the integrated control and go to Field Test Mode.
The menu will display the flame signal. Table 29 shows the
flame signal for the G71MPP unit.
Flame Signal in Microamps
Normal
2.6 or greater
NOTE − A much higher than normal micro amp reading
(15 for example) may appear when checking flame signal.
5/16"
Page 31
TABLE 29
Low Drop Out
2.5 or less 1.1
Sensor
FIGURE 11