Service manual

SYSTEM OPERATION
19
DEFROST CYCLE
Package Heat Pumps
The defrosting of the outdoor coil is jointly controlled by the
defrost control board, defrost (30/60) control and compres-
sor run time.
Solid State Timer
The defrost timer board can be connected for one of three
(3) time intervals. 30 minutes, 60 minutes, and 90 minutes
(Factory connected @ 60 min.). Package heat pumps manu-
factured after May 1999 (9905 Serial date code) will be
factory set @ 30 min.
The timing interval can not begin until the outdoor coil tem-
perature reaches approximately 30°F. (initiation tempera-
ture) at the defrost (30/60) control point of contact. As long
as this point of contact does not reach 60°F. (termination
temperature) the defrost timer board will count the number
of minutes that the compressor runs.
At the end of this (one of three) time interval, the defrost
board will call for defrost and enter the defrost mode. In this
mode the control board will energize the reversing relay,
de-energize the outdoor fan motor and energize the supple-
mental electric heat relay (if installed). When this occurs,
the outdoor fan motor stops and the reversing valve changes
to the cooling position sending hot refrigerant gas to the
outdoor coil, which will melt any frost accumulation.
The defrost control board will stay in the defrost mode until
the outdoor coil temperature reaches approximately 60°F.
at the point of contact with the defrost (30/60) control or a
maximum of 10 minutes compressor run time.
If the defrost cycle is terminated by temperature, then a
new time interval count can not begin until the defrost (30/
60) control again reaches approximately 30°F. at the point
of contact. If the defrost cycle was terminated by time, then
a new time interval could would begin immediately.
HEATING CYCLE
Package Gas Units
The heating cycle is accomplished by using a unique tubu-
lar design heat exchanger which provides efficient gas heat-
ing on either natural gas or propane gas fuels. The heat
exchangers compact tubular construction provides excel-
lent 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 combus-
tion. 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 mod-
ule. The module provides for field adjustment of the blower
delay at the end of the heating cycle. The range of adjust-
ment is for 60, 90, 120, or 180 seconds. The factory delay
setting is 30 seconds delay on 120 seconds delay off.
Honeywell Smart Valve Systems
Ignition is provided by an electronic ignition control and ce-
ramic glow bar or direct spark ignitor which heats to ap-
proximately 2500°F. A flame sensor then monitors for the
presence of flame and closes the gas valve if flame is lost.
The system may be controlled by most good heating and
cooling thermostats with an adjustable heat anticipator.
Some night setback thermostats that do not have a com-
mon terminal, use a power robbing circuit in the off cycle to
maintain the batteries. This type of thermostat may inter-
fere with the operation of the ignition control and should
not be used.
Direct Spark Ignition (DSI) Systems
Amana PGA__C, PGB__C and PGD__C units built after
July, 1999, are equipped with a direct spark ignition sys-
tem. Ignition is provided by 20,000 volt electronic spark. A
flame sensor then monitors for the presence of flame and
closes the gas valve if flame is lost.
The system may be controlled by most good heating and
cooling thermostats with an adjustable heat anticipator.
Some night setback thermostats that do not have a com-
mon terminal, use a power robbing circuit in the off cycle to
maintain the batteries. This type of thermostat may inter-
fere with the operation of the ignition control module and
should not be used.
HEATING SEQUENCE (Smart Valve and DSI Systems)
In order to illustrate the heating sequence, the following
has been simplified to give a better understanding of the
pressure switch operation.
Pressure Tap
Figure 8
Figure 8 is a view of the induced draft blower showing the
location of the pressure tap. The induced draft blower is
mounted on the the collector box, the Heat Exchanger ter-
minates into the collector box.