Service manual

20
SYSTEM OPERATION
The pressure tap has a predetermined orifice size for read-
ing static pressures. The induced draft blower motor as-
sembly is mounted to the collector box. When the motor is
in operation, a negative pressure will be created on the
pressure tap, collector box and heat exchanger flue pas-
sages.
A pressure control using a single pole, single throw electri-
cal switch is used as a safety device in case of a blocked
flue.
The figure 9 illustrates the pressure control in an off posi-
tion.
CONNECTOR
COMMON
TERMINAL
NORMALLY OPEN
TERMINAL
NEGATIVE PRESSURE
Figure 9
With the furnace in the off position the induced draft blower
motor will not be running. Atmospheric pressure will there-
fore be on both sides of the diaphragm and the electrical
switch will be open between (C) common and (NO) nor-
mally open terminals.
When the induced draft blower motor is in operation, the J-
tube hose will create a negative pressure on one side of
the diaphragm and atmospheric pressure will be on the other
side causing the diaphragm to move toward the negative
pressure.
This in turn will close the switch and make the (C) common
to the (NO) normally open terminals.
In the event of partially restricted or blocked flue the in-
duced draft blower will create less negative pressure and
at approximately -0.32" +.06 W.C. negative pressure would
open the contacts (C) to (NO).
OPERATING INSTRUCTIONS
1. Close the manual gas valve external to the unit.
2. Turn off the electrical power supply to the unit.
3. Set the room thermostat to its lowest possible setting.
4. Remove the heat exchanger door on the side of the
unit by removing screws.
5. This unit is equipped with an ignition device which auto-
matically lights the pilot. DO NOT try to light burner by
any other method.
6. Turn the gas control valve knob to the OFF position. Do
not force. Some Gas valves may have a different off/on
style switch.
OFF
ON
Figure 10
7. Wait five minutes to clear out any gas.
8. Smell for gas, including near the ground. This is impor-
tant because some types of gas are heavier than air. If
you have waited five minutes and you do smell gas,
immediately follow the instructions on the Page 8 of
this manual. If having waited for five minutes and no
gas is smell is noted, turn the gas control valve knob to
the ON position.
9. Replace the heat exchanger door on the side of the
unit.
10. Open the manual gas valve external to the unit.
11. Turn on the electrical power supply to the unit.
12. Set the thermostat to desired setting.
NOTE: There is approximate 20 second delay between
thermostat energizing and burner firing.
FAN OPERATION
Continuous Fan Mode
If the thermostat calls for continuous fan without a call for
heat or cool, the indoor blower will be energized at the heat
speed after a 7 second on delay. The fan remains ener-
gized as long as there is not a call for heat or cool. Once
the call for continuous fan is de-energized, the indoor blower
will go through a 30 second off delay.
If a call for cool occurs during continuous fan operation, the
blower will switch to the cooling speed after the 7 second
cool on delay.
If a call for heat occurs during continuous fan operation,
the indoor blower will de-energize when the heat on blower
delay begins. The heat cycle will control the indoor blower
operation until the heat blower off delay is over. The con-
tinuous fan mode will function normally even while the con-
trol is in heat lockout.