Heating Operation And Adjustments; Electric Heat Start-Up - Lennox LHT078H Installation Instructions Manual

Heating Operation and Adjustments

(Gas Units)
A-Heating Sequence of Operation
1- On a heating demand the combustion air inducer
starts immediately.
2- Combustion air pressure switch proves inducer
operation. After a 30-second pre-purge, power is
allowed to ignition control. Switch is factory set and
requires no adjustment.
3- Spark ignitor energizes and gas valve solenoid
opens.
4- Spark ignites gas, ignition sensor proves the flame
and combustion continues.
5- If flame is not detected after first ignition trial, ignition
control will repeat steps 3 and 4 two more times
before locking out the gas valve.
6- For troubleshooting purposes, an ignition attempt
after lock out may be re-established manually. Move
thermostat to "OFF" and return thermostat switch to
"HEAT" position.
B-LDT Heating Stages
TABLE 10
Outdoor Ambient
Temperature
Above Balance Point Compr. 1 & 2 On*
Temperature Setting** Gas Heat Off
Below Balance Point Compr. 1 & 2 Off
Temperature Setting** Gas Heat Low
*L1 and L2 reversing valves are de-energized with a
heating demand. The heat pump will heat only, not cool.
**Balance Point temperature setting can be adjusted
using the following mobile service app menu path:
RTU MENU>SETUP>INSTALL>??
W1 Demand W2 Demand
Compr. 1 & 2 Off
Gas Heat High
Compr. 1 & 2 Off
Gas Heat High
C-Limit Controls
Limit controls are factory-set and are not adjustable. The
primary limit is located on the blower deck to the right of
the blower housing.
D-Heating Adjustment
Main burners are factory-set and do not require adjustment.
The following manifold pressures are listed on the gas valve.
Natural Gas Units - Low Fire - 1.6" w.c.
Natural Gas Units - High Fire - 3.7" w.c.
LP Gas Units - Low Fire - 5.5" w.c.
LP Gas Units - High Fire - 10.5" w.c.
Electric Heat Start-Up (LHT Units)
Factory- or Field-Installed Option
A W1 demand will energize compressors 1 and 2. An
increased W2 heating demand will energize electric heat.
W1 will also energize electric heat during defrost to
maintain discharge air temperature.
Note - L1 and L2 reversing valves are de-energized with a
heating demand. The heat pump will heat only, not cool.
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(not adjustable)
(not adjustable)