McQuay IM-685-1 Installation Manual
Installation and Maintenance Manual IM-685-1
TM
SuperMod
Forced Draft Gas Fired Furnace
on McQuay Applied Rooftop Systems
HT***A* with RM7895A Flame Safeguard
Group:
Part Number:
Date:
Applied Systems
June 2001
IM685
© 2001 McQuay International
IM 685-1 1
When writing to McQuay for service or replacement parts, refer to the model number of the unit as stamped on the serial plate,
attached to the unit. If there is an in-warranty failure, state the date of installation of the unit and the date of failure along with an
explanation of the malfunctions and the description of the replacement parts required. Parts are warranted for ninety (90) days
unless covered by original unit warranty.
General
Warranty Exclusion .......................................................... 3
Ventilation and Flue Pipe Requirements.......................... 3
Factory Mounting............................................................. 3
Factory Checkout ............................................................. 3
Installation
General ............................................................................. 3
Flue Box ........................................................................... 3
Wind Deflector................................................................. 4
Electrical........................................................................... 4
Gas Pressure Requirements.............................................. 4
Gas Piping ........................................................................ 4
Valve and Regulator Venting............................................ 5
Normally Open Vent Valve .............................................. 6
Gas Piping Routing into Unit........................................... 6
On-the-Roof Piping (Models 020-140) ........................ 6
Through-the-Curb Piping (Models 020-140)................ 6
Typical Piping Connections.......................................... 6
Gas Piping (Models 150-200)....................................... 7
Gas Piping Within the Vestibule................................... 7
Field Gas Piping Required............................................ 7
Condensate Drain.......................................................... 7
Vestibule (Models 150-200) ......................................... 7
Start-up & Operating Procedures
Start-up Responsibility..................................................... 8
Start-up Procedure............................................................ 8
Before Start-up ................................................................. 8
About This Burner............................................................ 8
Prepurge is Low-High-Low.......................................... 8
Low Fire Start............................................................... 8
"Pilot" is Main Flame Modulated Down
to Pilot Rate ................................................................ 8
Set Control System to Enable Heating............................. 8
Start-up Preliminary ......................................................... 8
Preliminary "Dry" Run..................................................... 9
Flame Start-up .................................................................. 9
Modulate Firing Rate ....................................................... 9
Combustion Tests ........................................................... 10
Cycle the Unit................................................................. 10
Record Data.................................................................... 10
References
Typical Electrical Schematic .......................................... 10
Typical Sequence of Operation ...................................... 10
Typical Piping Schematic................................................11
Typical Burner Control Box........................................... 12
Flame Safeguard
Keyboard Display Module..............................................12
Operation.........................................................................12
Normal Start-up ..............................................................12
LED Display ...................................................................12
Service
General............................................................................13
Gun Assembly.................................................................13
Gun Assembly Removal and Installation .......................13
Flame Rod Adjustment ...................................................13
Flame Rod Installation....................................................13
Ignition Electrode Adjustment........................................13
Air & Gas Adjustments...................................................14
Gas Supply Pressure .......................................................14
High Pressure Regulator .................................................14
Gas Adjustment...............................................................14
Air Adjustment................................................................14
Air and gas Control Linkage...........................................14
Actuator Crankarm..........................................................15
Switch Adjustments ........................................................15
Altitude Considerations ..................................................15
Gas Valve Pressure Regulator Adjustment .....................16
Adjustment Procedure for Parallel Valves ......................16
Check Manifold Pressure at Minimum rate ....................16
Combustion Testing ........................................................17
Verify Input Rate .............................................................17
Check CO
, CO and Stack Temperature .........................17
2
Cleaning Heat Exchanger (Models 032-200) .................17
Cleaning Heat Exchanger (Models 020-025) .................18
Leakage Symptoms.........................................................18
Checking for Leaks.........................................................18
Causes of Failures ...........................................................18
Replacing a Heat Exchanger...........................................19
Furnace Condensation ....................................................19
Rear Cleanout Port..........................................................20
Furnace Condensate Drain Kit........................................20
Considerations.............................................................20
Install .875 Copper Drain Line....................................20
Install the Cover Over Drain Pipe ...............................20
Combination Fan and Limit Control...............................20
Maintenance
Monthly, Twice Yearly, Yearly........................................21
Troubleshooting Chart ....................................................22
Typical Parts List - 60 Hz ...............................................24
Capacities & Adjustments Table
Performance & Service History
..........................25
............................26
SERVICED BY:
TELEPHONE NO: INSTALLATION DATE:
Installer: Leave this manual with owner. It is to be posted and maintained in legible condition.
2 IM 685-1
General
This forced draft gas burner is specifically designed for use
with the furnace on McQuay applied rooftop heating and air
conditioning units which are for outdoor installation only.
Each model size has unique burner head components to tailor the shape of the flame to each particular stainless steel
combustion chamber, to match the capacity requirement, and
to offer a desirable turndown potential when arranged for
modulation. This is a forced draft burner with a high pressure combustion air fan and will operate against pressure.
This eliminates the need for draft inducers, chimneys, draft
hoods, barometric dampers, and Breidert caps.
Warranty Exclusion
Warranty is void if furnace is operated in the presence of
chlorinated vapors, if the airflow through the furnace is not
in accordance with rating plate, or if the wiring or controls
have been modified or tampered with.
WARNING
Units equipped with gas heating must not be operated
in an atmosphere contaminated with chemicals which
will corrode the unit such as halogenated hydrocar-
bons, chlorine, cleaning solvents, refrigerants, swim-
ming pool exhaust, etc. Exposure to these compounds
may cause severe damage to the gas furnace and result
in improper or dangerous operation. Operation of the
gas furnace in such a contaminated atmosphere consti-
tutes product abuse and will void all warranty coverage
by the manufacturer. Questions regarding specific con-
taminants should be referred to your local gas utility.
Ventilation & Flue Pipe Requirements
The McQuay applied rooftop unit is equipped with an outdoor air louver to supply adequate combustion air. The unit
also has a flue outlet assembly and requires no additional
chimney, flue pipe, Breidert cap, draft inducer, etc.
Factory Mounting
This burner and gas train has been installed and wired at the
factory. See "Gas Piping." Also note that models 150
through 200 have the burner removed for shipment; see
"Installation: Models 150-200."
Factory Checkout
This complete heating plant was fired and tested at the factory. It was adjusted to the required capacity and efficiency.
Modulating air and gas linkages, pressure regulators, and
stops were adjusted for proper operation at all firing levels.
The unit was fired through several complete start-up through
shutoff sequences to check operation. A check was made of
the air switch, gas pressure switch, high limit operation, and
combustion characteristics including C0
and CO (at several
2
firing rates on modulating burners).
If the burner was specified for operation at higher altitudes,
combustion air adjustments were compensated to result in
proper settings at the higher altitude. This checkout normally eliminates on-the-job start-up problems; however, the
equipment is subject to variable job conditions and shipping
shocks can change adjustments, cause damage, and loosen
connections and fasteners. Therefore, it is necessary to go
through the complete start-up procedure even though the
unit may appear to be operating properly.
Installation
General
The installation of this equipment shall be in accordance
with the regulations of authorities having jurisdiction and all
applicable codes. It is the responsibility of the installer to
determine and follow the applicable codes. Sheet metal
parts, self-tapping screws, clips, and such items inherently
have sharp edges, and it is necessary that the installer exercise caution. This equipment is to be installed by an experienced professional installation company that employs fully
trained technicians.
Flue Box
The flue box is not installed at the factory because it would
increase the width of the unit beyond the allowable shipping
width. All holes are prepunched, the fasteners are furnished
and everything is shipped inside the burner vestibule of the
unit. On Models 150 through 200 it is shipped in the same
crate as the vestibule. Remove and discard the shipping
cover installed over the furnace tube outlets before installing
the flue box.
1. Remove the screws (2) in the casing of the unit that line
up with the bottom lip holes of the flue box tube sheet
(3). These screws will later be replaced, at which time
they will also attach the bottom of the flue box to the
unit.
2. Install the flue box tube sheet (3), attaching top to roof
dam strip with screws (1). Do not attach bottom at this
time.
3. Apply a 1/8 to 3/16 inch bead of high temperature silicone around each tube to seal it to the flue box tube sheet
(3) and prevent condensate from running back toward the
unit along the outside of the tube. See Figure 1. Also
apply a bead of high temperature silicone to seal both
sides to the bottom of the flue box wrapper (4), being
careful not to obstruct the square drain holes in each front
corner.
4. Install flue box wrapper sheet (4) by sliding it up from
below so as not to disturb the silicone seal described in
3 above. Attach with side screws (5). At this time rein-
stall bottom screws (2)
.
IM 685-1 3
Figure 1. Flue Box
4
Seal Around
Each Tube
Seal Side
Seams
Electrical
3
5
The McQuay burner receives its electrical power from the
main unit control panel. No additional power wiring must be
routed to the burner. The sequencing of the burner is also
controlled through this panel and therefore is factory wired.
No additional wiring will be required. Note that models 150
1
through 200 furnaces require reassembly of some electrical
connections as the burner is removed for shipment.
WARNING
Improper installation, adjustment, alteration, service or
maintenance can cause property damage, injury or
death. Read the installation, operating and maintenance
instructions thoroughly before installing or servicing
this equipment.
FOR YOUR SAFETY
If you smell gas:
1. Open Windows
2. Don’t touch electrical switches.
3. Extinguish any open flame.
4. Immediately call your gas supplier.
FOR YOUR SAFETY
Drain Open ing
(both corners)
2
Wind Deflector
The wind deflector is not installed at the factory because it
would increase the width of the unit beyond the allowable
shipping width. The deflector is shipped in the burner vestibule of the unit. Install the wind deflector over the combustion air intake opening of the burner compartment before
operating the burner. Use inner hinge screws on top hinged
door (see Figure 2). Side hinged doors have holes for mounting (see Figure 5). Models 020 and 025 have a different style
wind deflector. It mounts on the door and has a top opening
flush with the roof of the unit (see Figure 14).
Figure 2. Wind Deflector (Models 032 thru 140)
Tube Ends
3
Flue Box
Tube Sheet
4
Flue Box
Wrap
The use and storage of gasoline or other flammable
vapors and liquids in open containers in the vicinity of
this appliance is hazardous.
Gas Pressure Requirements
The pressure furnished to the combination gas control(s)
must not exceed 13.9 in. W.C. When the supply pressure is
above 13.9 in. W.C. a high pressure regulator must precede
the combination gas control(s). The inlet gas pressure cannot
exceed the maximum pressure rating of the high pressure
regulator and the outlet pressure must be such that it will
furnish gas to the appliance pressure regulator within the
pressure range mentioned above, preferably at 7.0 in. W.C.
when firing at maximum rate.
Gas Piping
The connection size at the burner is shown in Table 5 under
Column 13 thru 15. Gas piping must be sized to provide the
minimum required pressure at the burner when the burner is
operating at maximum input. Consult the appropriate local
utility on any questions on gas pressure available, allowable
piping pressure drops, and local piping requirements.
Install all piping in accordance with the National Fuel Gas
Code (ANSI Z223.1), (NFPA 54-1999) and any applicable
local codes.
Wind Deflector
Hinge Inner
Screw
Burner
Access
Door
4 IM 685-1
It is very important that the proper size piping be run from
the meter to the gas burner without reductions. Undersized
piping will result in inadequate pressure at the burner. The
pressure will be at its lowest when it is needed the most, at
times of maximum demand. Therefore, it can cause intermittent hard-to-find problems because the problem may have
left before the service technician has arrived. Avoid the use
of bushings wherever possible.
Remove all burrs and obstructions from pipe. Do not bend
pipe; use elbows or other pipe fittings to properly locate
pipe. A drip leg must be installed in the vertical line before
each burner such that it will not freeze. Install unions so gas
train components can be removed for service. All pipe
threads must have a pipe dope which is resistant to the
action of LP gas. After installation, pressurize the piping as
required and test all joints for tightness with a rich soap
solution. Any bubbling is considered a leak and must be
eliminated. Do not use a match or flame to locate leaks.
Table 1. Capacity of pipe natural gas (CFH)
WITH PRESSURE DROP OF .3" W.C. & SPECIFIC GRAVITY OF 0.60
PIPE
LENGTH (FT.)
10 132 278 520 1050 1600 2050 4800 8500 17500
20 92 190 350 730 1100 2100 3300 5900 12000
30 73 152 285 590 890 1650 2700 4700 9700
40 63 130 245 500 760 1450 2300 4100 8300
50 56 115 215 440 670 1270 2000 3600 7400
60 50 105 195 400 610 1150 1850 3250 6800
70 46 96 180 370 560 1050 1700 3000 6200
80 53 90 170 350 530 990 1600 2800 5800
90 40 84 160 320 490 930 1500 2600 5400
100 38 79 150 305 460 870 1400 2500 5100
125 34 72 130 275 410 780 1250 2200 4500
150 31 64 120 250 380 710 1130 2000 4100
175 28 59 110 225 350 650 1050 1850 3800
200 26 55 100 210 320 610 980 1700 3500
½¾ 11¼1½22½3 4
Valve & Regulator Venting
Valve diaphragm vents, pressure regulator vents, and pressure switch vents are located in the outdoor burner vestibule
and therefore vent tubing is not run to the outside of this vestibule. If local regulations require that this be done, it is a
part of the field gas piping hookup. Remove any plastic protector plugs from regulator and valve vents.
Normally Open Vent Valve
Vent valves such as required by IRI for over 1000 MBH
input units must always be routed to the outdoors. This is
field piping.
PIPE SIZE-INCHES (IPS)
Use multiplier below for other gravities and pressure drops.
Note:
Table 2. Specific gravity other than 0.60
SPECIFIC GRAVITY MULTIPLIER
0.50 1.100
0.60 1.000
0.70 0.936
0.80 0.867
0.90 0.816
1.00 0.775
Table 3. Pressure drop other than 0.3"
PRESSURE
DROP
0.1 0.577 1.0 1.83
0.2 0.815 2.0 2.58
0.3 1.000 3.0 3.16
0.4 1.16 4.0 3.65
0.6 1.42 6.0 4.47
0.8 1.64 8.0 5.15
MULTIPLIER PRESSURE MULTIPLIER
IM 685-1 5
Gas Piping Routing Into Unit
On-The-Roof Piping (Models 020-140)
1. Remove knockout (1) at corner of burner vestibule door
and saw out corner of door. See Figure 3b. Make saw cuts
(2) tangent to round hole and square with door edges.
2. Install pipe corner plate (3) on vestibule, locating on prepunched holes. See Figure 3c. This part is shipped inside
the vestibule.
3. Route gas supply pipe through hole. Carefully plan pipe
route and fitting locations to avoid interference with
swinging of doors, etc.
Through-The-Curb Piping (Models 020-140)
1. Remove bottom access panel (5). See Figure 3c.
2. Remove knockout (4) and make an opening (6) through
bottom deck directly below knockout hole.
3. Route gas pipeline through these openings and seal them
off with suitable grommets (7).
See Figure 3a Section A-A.
4. Replace bottom access panel (5).
Figure 3a.
A
2
1
2
See Figure 3c
Figure 3b.
Typical Piping Connections
Figure 4.
Figure 3c.
4
7
7
A
4
6
3
5
Gas Supply
Section A-A
FSG
A
C
D
With Shutoff Cock
Folded Back
Figure 4b. Figure 4a.
A = Shutoff Cock (ball valve)
B = Union - Furnished.
C = Gas Pipe - Routed in through front
D = Gas Pipe - Routed in through curb
E = Factory Piped Gas Trains
6 IM 685-1
D
With Shutoff Cock
In Front
C
A
B
E
Gas Piping (Models 150 thru 200)
The gas piping cannot be routed up to the burner from
within the curb on Models 150 through 200. Gas piping
must be routed across the roof to under the burner vestibule, or a pitch pocket can be provided there. The installer
must cut a hole in the bottom panel of the overhanging
burner vestibule through which to route the gas line up to
the burner gas train. The bottom panel of the vestibule is
at approximately the same elevation as the top of the curb.
Gas Piping within the Vestibule
The gas piping layout within the vestibule will vary
according to the complexity and size of the gas train relative to the available room within the vestibule. As an
example, a gas train with a high pressure regulator and an
extra safety shutoff valve (when required for IRI, etc.) will
require careful use of the available space. The examples
shown in Figure 4 indicate typical piping layouts.
Field Gas Piping Required
The gas train components have all been factory installed
and require only a connection to the supply gas line. The
manual shutoff valve is located within the burner vestibule. If local codes require a manual shutoff valve that is
is accessible from outside the unit, that valve must be relocated
or an additional valve added. In locating such a valve, it is to
be readily accessible and located such that no obstructions
interfere with operation of the handle. See Figure 16a, "Valve
and Regulator Venting", and "Normally Open Vent Valves".
Condensate Drain
Models 020 and 025 are equipped with a 3/4" I.P. condensate
drain pipe projecting from the back side of the furnace section
(see Figure 14). If applicable codes or regulations requires this
can be trapped and/or routed to a drain. Also see "Furnace
Condensation" section.
Vestibule (Models 150 thru 200)
These two furnace sizes exceed the allowable shipping width
and for this reason the burner is disconnected and removed for
shipment. A sheet metal vestibule weather enclosure is also
disassembled for shipment. At installation the burner must be
re-mounted, the tagged electrical connections re-attached, and
the vestibule re-assembled and mounted as shown in Figure 5.
These items are packed in a crate and shipped as a separate
item.
Figure 5.
#10 Screw
Fasten Wind Deflector
To Door With #10 Screws,
(Door & Wind Defletor
Part of Vestibule Kit)
Side Panel
Cut Gas Line Opening
Door
Top Panel
Hinge
Side Panel,
With Latch
Door
Bottom Panel
IM 685-1 7
Start-up & Operating Procedures
Start-up Responsibility
The start-up organization is responsible for determining that
the furnace, as installed and as applied, will operate within
the limits specified on the furnace rating plate.
1. The furnace must not exceed the specified "Maximum
MBH Input." See "Verify Input Rate."
2. The furnace must not operate at an airflow below the
specified "Minimum Airflow CFM." On variable air volume systems it must be determined that the furnace will
not be operated if or when system cfm is reduced below
the specified minimum airflow cfm.
3. It must be established that the gas supply is within the
proper pressure range. See "Gas Pressure Requirements."
Start-up Procedure
Only qualified personnel should perform the start-up and
service of this equipment. It is highly recommended that the
initial start-up and future service be performed by McQuay
certified technicians who are familiar with the hazards of
working on live equipment. A representative of the owner or
the operator of the equipment should be present during startup to receive instructions in the operation, care and adjustment of the unit.
WARNING
a prepurge cycle occurs, the air control valve will be repositioned to the maximum position for the prepurge and then
returned to the minimum position for low fire start.
Low Fire Start
The burner is controlled for proven low fire start. The actuator will position the modulating gas valve and the modulating air valve to the low fire position each time the burner is
to light off. Switch LS1 proves the air and gas valves are at
the low fire position. If LSl is not "made" at light off, the gas
valves cannot open and the flame safeguard will lock out,
requiring manual reset.
"Pilot" is Main Flame Modulated Down to Pilot Rate
The "pilot" is not a separate flame or burner. The "pilot" is
the main flame operating at its minimum rate. That minimum rate is so low that it qualifies as a pilot burner.
Set Control System to Enable Heating
To allow start-up and check-out of the burner, the control
system must be set to call for heating and must he used to
control the amount of heating. Set the control system to call
for heat so MCB-B011 energizes Relay R20. With MCBB011 closed, vary the temperature control set point to
increase, maintain, or reduce the firing rate of the burner as
required for these tests. If MCB-B09 is closed the firing rate
will decrease. If MCB-B010 is closed the firing rate will
increase. If neither are "made" the firing rate will remain
unchanged.
Should overheating occur or the gas supply fail to shut
off, turn off the manual gas valve to the appliance before
shutting off the electrical supply.
Before Start-up
1. Notify any inspectors or representatives that may be
required to be present during start-up of gas fuel equipment. These could include the gas utility company, city
gas inspectors, heating inspectors, etc.
2. Review the equipment and service literature and become
familiar with the location and purpose of the burner controls. Determine where the gas and power can be turned
off at the unit, and upstream of the unit.
3. Verify that power is connected to the unit and available.
4. Verify that the gas piping, meter, and service regulator
has been installed, tested, and is ready to go.
5. Verify that proper instruments will be available for the
start-up. A proper start-up requires the following: voltmeter, manometer or gauges with ranges for both manifold
pressure and inlet gas pressure, keyboard display module
or a 20K ohm/volt meter for flame safeguard signal
strength measurement, CO
indicator, and a stopwatch for timing the gas meter.
About This Burner
Prepurge is Low-High-Low
The burner air control valve will be at the minimum position
during off cycles. Upon a call for heat or any other time that
indicator, carbon monoxide
2
Start-up Preliminary
1. Before energizing the burner verify that the modulating
air and gas valve mechanism moves freely and is not
binding, and check the linkage fasteners for tightness.
This can be accomplished without affecting any adjustments. Remove shoulder screw (12), Figure 16a, that
connects the teflon bushing to the actuator crank arm.
The control rod can now be manually moved back and
forth, it should feel smooth with no binding or scraping.
Always remove shoulder screw (12) and test for binding
after reinstalling the gun assembly on Models HT050-
200.
2. Close the gas line cocks. Install a Keyboard Display
Module, Honeywell Part No. S7800A1001, or connect a
20K ohm/volt meter to the test jack on the flame safeguard (see Figure 7).
3. Check the burner fan wheel for binding, rubbing, or loose
set screws.
4. Check power. Position switch S3 on burner control panel
to AUTO. The LED marked POWER on the flame safeguard should come on and after a 10 second "Initiate"
period the burner motor should start. Check for (CW)
rotation as viewed through the burner fan housing inlet. If
the motor does not start, press the reset button on the
flame safeguard. If the motor still does not start, consult
the appropriate section of the "Troubleshooting Guide".
Continue on to Item 5 when burner motor will run 10 seconds after the switch is positioned to AUTO.
8 IM 685-1
5. Check voltage. With burner switch S3 at AUTO, measure
voltage across burner control box terminals 2 and NB. If
it is not between 114 and 126 volts, check the voltage and
tapping connections to the supplying transformer at the
unit main control panel.
6. Purge the gas lines. Turn off electrical power. Remove
the 1/8 inch pipe plug from the inlet pressure tap of the
first electric gas valve in the line, open the gas line cocks
upstream from there and bleed the gas line of all air.
Replace the1/8 inch pipe plug.
7. Leak check. Using a rich soap-water mixture and a brush,
check the gas lines for leaks. Correct all leaks before
starting burner. After the burner is operating and all the
downstream valves are open, leak check that portion of
the gas train.
8. Connect a manometer to measure gas manifold pressure
at (1), Figure 16a. There is a 1/8 inch pipe size plugged
tapping in the gas line just before it enters the burner
housing.
Preliminary "Dry" Run
1. Close the gas line cock, Remove the burner front cover
and open the control panel door. Switches LS1 and LS2
in the lower right hand corner of the control box should
be in view and the modulating actuator VM1 should be at
the minimum rate position. Verify that the right hand
switch LS1 is being held in the 'made' position by the collar on the control rod and that the switch lever is not bottomed out against the plastic switch housing.
2. Position the burner switch S3 to AUTO. The flame safeguard will go through a 10 second "Initiate" period, after
which the burner motor will start. The modulating gas
valve actuator VM1 will drive the air valve and gas valve
to the maximum rate position. Observe the linkage for
any binding, loose fasteners, or other problems that could
have resulted from shipping.
3. When the actuator reaches the maximum rate position,
verify that the left hand switch LS2 is held in the 'made'
position by the collar on the control rod and that the
switch lever is not bottomed out against the plastic switch
housing.
4. Position the burner switch S3 to OFF. Close the control
panel door and reinstall the burner front cover. Prepare to
measure the burner air box pressure by holding a rubber
manometer tube tightly over port
tube must surround the hole and seal tightly against the
burner housing to measure the static pressure through the
hole.
5. Position the burner switch S3 to AUTO and with the
burner actuator VM1 at the maximum rate position mea-
sure the burner air box pressure at port
The actuator will remain at this position for the first 20
seconds of the prepurge period. Typical static pressure
readings are listed in Table 5, Column 6. Any appreciable
deviation from these values would indicate a burner air
problem that should be found before attempting to fire
➃
, Figure 16b. The
➃
, Figure 16b.
the burner. These problems could include linkages disturbed during shipment, etc.
Flame Start-up
1. Open the gas line cocks and position switch S3 to AUTO.
The flame safeguard will go through the 10 second "Initiate" period, after which the burner motor will start. The
modulating air and gas valve actuator VM1 will drive the
air valve to the full open position. At full open the 60 second prepurge period will begin. After 20 seconds at maximum open, the actuator will begin a 30 second stroke to
reposition the air valve back to the minimum position.
Upon completion of the 60 second prepurge cycle, gas
valve GV1 will open (as indicated when the LED marked
PILOT comes on), the ignition transformer is powered
and the flame should come on at minimum rate.
2. Observe the gas manifold pressure manometer during this
sequence. The manifold pressure should be close to zero
(it will indicate a slight heat exchanger pressure caused
by the burner combustion air fan). When gas valve GV1
opens it should indicate a manifold pressure approximate
to the values listed in Table 5, Column 10. Approximately 3 seconds after GV1 is powered the flame will
come on and the flame signal will read 1.5 to 5.0 volts
DC. The LED marked FLAME will come on when flame
is detected and the LED marked MAIN will come on if
flame is being detected at the end of the 10 second trail
for ignition period. When the LED marked MAIN comes
on gas valves GV4-GV8 (when included) will also open
and the firing rate will be determined by the control system. On the initial start-up if the flame does not light and
the flame safeguard locks out, reset it and make several
attempts to light before assuming there are problems
other than more air in the gas lines. If initial flame operation is erratic wait until after a period of main flame operation has further purged the gas lines before trying to
"adjust out" something that may actually be caused by air
in the lines.
Modulate Firing Rates
Set the temperature control system so the burner actuator
VM1 will modulate to increase the firing rate. Observe the
flame signal and the manifold pressure manometer as this is
occurring. The flame signal should remain between 1.5 to
5.0 volts DC through the entire range of the burner, and the
manifold pressure should be between the values indicated by
Table 5, Column 9 and 10. If the manifold pressure shoots
above these values and then slowly returns to normal as the
burner is modulating down to a lower firing rate, isolate
which combination gas control is causing this. Check that
valves pressure regulator adjustment per "Gas Valve Pressure Regulator Adjustment" section. If this condition cannot
be adjusted out, replace the valve. If combustion appears
normal, proceed with the combustion test.
IM 685-1 9
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