Air Shutter Adjustment; Control Operating Sequence - Modine Manufacturing IFS Installation And Service Manual

START-UP PROCEDURE

Air Shutter Adjustment

Proper operation provides a soft blue flame with a well-defined
inner core. A lack of primary air will reveal soft yellow-tipped
flames. Excess primary air produces short, well-defined flames
with a tendency to lift off the burner ports. For both natural
and propane gas, the air shutters can be adjusted to control
the burner flame height. The air shutters can be accessed by
reaching behind the manifold tee shown in Figure 23.1. The
larger models may require the removal of the manifold (see
Manifold Assembly Removal).
Natural Gas Flame Control
Control of burner flames on duct furnaces utilizing natural gas
is achieved by resetting the primary air shutters (See Figure
23.1) to either increase or decrease primary combustion air.
Prior to flame adjustment, operate duct furnace for about fifteen
minutes. The main burner flame can be viewed after loosening
and pushing aside the gas designation disc on the side of the
burner box.
To increase primary air, loosen the air shutter set screws and
move the air shutters closer to the manifold until the yellow-
tipped flames disappear. (See Figure 23.1 for air shutter and
heat exchanger support locations.) To decrease primary air,
move the air shutters away from the manifolds until flames
no longer lift from burner ports, but being careful not to cause
yellow tipping. Retighten set screws after adjustment.
Propane Gas Flame Control
An optimum flame will show a slight yellow tip. Prior to flame
adjustment, operate furnace for at least fifteen minutes. Loosen
air shutter set screws and move the air shutters away from the
manifold to reduce the primary air until the yellow flame tips
appear. Then increase the primary air until yellow tips diminish
and a clean blue flame with a well defined inner cone appears.
14
IMPORTANT
To prevent premature heat exchanger failure, with all control
systems, a blower starting mechanism must be provided so
that the blower is running or energized within 45 seconds of
the gas control operation.

Control Operating Sequence

Duct furnaces are supplied with intermittent pilot systems with
continuous retry, which both the main burner and pilot burner
are turned off 100% when the thermostat is satisfied. On a call
for heat, the system will attempt to light the pilot for 70 seconds.
If the pilot is not sensed for any reason, the ignition control will
wait for approximately six minutes with the combination gas
control closed and no spark. After six minutes, the cycle will
begin again. After three cycles, some ignition controllers lockout
for approximately one hour before the cycle begins again. This
will continue indefinitely until the pilot flame is sensed or power
is interrupted to the system.
Note: Gas Control Options (see page 16) could change the
listed sequence of operation based on their function.
The descriptions given are for the basic duct furnace.
Single Furnace Controls
Staged Control (Digit 12=1 or 2):
These units utilize a single- or two-stage combination gas valve,
an ignition control, and a low voltage thermostat.
Electronic Modulating Control (Digit 12=4, 7, or 8):
These units utilize a single-stage combination gas valve, an
electronic modulating gas valve, a modulating amplifier, an
ignition control, and one of the following:
• Modulating room thermostat
• Modulating duct thermostat with remote temperature set point
adjuster
• Building Management System (BMS) signal by others (an
inverted signal where 0 VDC or 4 mA is high fire and 10 VDC
or 20 mA is low fire).
The control operating sequence for all units is as follows:
1. The thermostat calls for heat. For BMS controlled units, the
BMS closes a heat enable contact at the unit.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed, the
differential pressure switch closes. The power exhauster pre-
purge time delay relay then closes after 20 to 40 seconds and
energizes the gas control circuit.
3. The pilot valve opens and the spark igniter sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts).
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark igniter from sparking.
5. The main gas valve is opened and the main burner is
controlled as follows:
a. Single-Stage Units: The main burner is lit to 100% full fire.
b. Two-Stage Units: The main burner is lit to 50% fire. If
the temperature at the thermostat continues to fall, the
thermostat will call for high stage heat and the main burner
is lit to 100% full fire.
c. Modulating Thermostat (Room or Duct): The main
gas valve is opened 100% and the burner firing rate is
modulated between 40% and 100% full fire. A resistance
AIR 5-593.9