Service Manual

PRODUCT DESIGN
20
Direct Spark Ignition (DSI) Systems
APD/GPD units are equipped with a direct spark ignition
system. Ignition is provided by 22,000 volt electronic spark.
A flame sensor then monitors for the presence of flame and
closes the gas valve if flame is lost.
HEATING CYCLE
On a call for first stage heat, the contacts of the room
thermostat close. This energizes terminals R to Y and R to
G, the low voltage circuit to the contactor is completed
starting the compressor and outdoor fan motor. This also
energizes the EEM motor after approximately 6-seconds.
When the thermostat is satisfied, breaking the circuit be-
tween R to Y and R to G, the compressor and outdoor fan
motor will stop. The indoor blower will stop after a pro-
grammed 60 second off delay.
NOTE: Should the second stage heating contacts in the room
thermostat close, a W1 signal will be sent to the ignition
control and the Y signal would be removed. A normal gas
heating sequence would then follow.
HEATING/ GAS & L.P.
The heating cycle is accomplished by using a unique tubular
design heat exchanger which provides efficient gas heating
on either natural gas or propane gas fuels. The heat
exchangers compact tubular construction provides excellent
heat transfer for maximum operating efficiency.
Inshot type gas burners with integral cross lighters are used
eliminating the need for adjustable air shutters. The same
burner is designed for use on either natural or propane gas
fuels.
The induced draft blower draws fuel and combustion air into
the burners and heat exchanger for proper combustion. A
pressure switch is used in conjunction with the I. D. blower
to detect a blocked flue condition.
Blower operation is controlled by the ignition control module.
The module allows for field adjustment of the blower delay at
the end of the heating cycle. The range of adjustment is for
90, 120, 150 or 180 seconds. The factory delay setting is 30
seconds delay on 150 seconds delay off.