McQuay IM 685, SuperMod IM 685 Installation Manual
Installation & Maintenance Manual
®
SuperModTM Forced Draft Gas Fired Furnace
on McQuay Applied Rooftop Systems
HT****A* with RM7895A Flame Safeguard
(Gas Burner)
IM 685
Group: Applied Systems
Part Number: 629948Y-00
Date: March 1998
©1998 McQuay International
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.
Table of Contents
General
Warranty Exclusion ........................................................ 3
Ventilation and Flue Pipe Requirements ........................ 3
Factory Mounting .......................................................... 3
Factory Checkout ........................................................... 3
Installation
General ........................................................................... 3
Flue Box ......................................................................... 4
Wind Deflector .............................................................. 4
Electrical ......................................................................... 5
Gas Pressure Requirements ............................................. 5
Gas Piping ...................................................................... 5
Valve and Regulator Venting .......................................... 6
Normally Open Vent Valve ............................................ 6
Gas Piping Routing Into Unit
On-the-Roof Piping (Models 020-140) ...................... 7
Through-the-Curb Piping (Models 020-140) ............. 7
Typical Piping Connections ........................................ 7
Gas Piping (Models 150-200) ..................................... 8
Gas Piping Within the Vestibule ................................ 8
Field Gas Piping Required .......................................... 8
Condensate Drain ....................................................... 8
Vestibule (Models 150-200) ....................................... 8
Start-up & Operating Procedures
Start-up Responsibility ................................................... 9
Start-up Procedure.......................................................... 9
Before Start-up ............................................................... 9
About This Burner ......................................................... 9
Prepurge is Low-High-Low ......................................... 9
Low Fire Start ............................................................. 9
“Pilot” is Main Flame Modulated Down
to Pilot Rate ............................................................ 9
Set Control System to Enable Heating ......................... 10
Start-up Preliminary ..................................................... 10
Preliminary "Dry" Run................................................. 10
Flame Start-up .............................................................. 11
Modulate Firing Rate ................................................... 11
Combustion Tests ........................................................ 11
Cycle the Unit .............................................................. 11
Record Data ................................................................. 11
References
Typical Electrical Schematic ......................................... 12
Typical Sequence of Operation..................................... 12
Typical Piping Schematic ............................................. 13
Typical Burner Control Box ......................................... 14
Flame Safeguard
Keyboard Display Module ............................................ 14
Operation ..................................................................... 14
LED Display................................................................. 15
Service
General ......................................................................... 16
Gun Assembly .............................................................. 16
Gun Assembly Removal and Installation ...................... 16
Flame Rod Adjustment ................................................. 16
Flame Rod Installation ................................................. 17
Ignition Electrode Adjustment ..................................... 17
Air and Gas Adjustments .............................................. 17
Gas Supply Pressure...................................................... 17
High Pressure Regulator ............................................... 17
Gas Adjustment ............................................................ 17
Air Adjustment ............................................................. 17
Air and Gas Control Linkage ........................................ 18
Actuator Crankarm....................................................... 19
Switch Adjustment ....................................................... 19
Altitude Considerations ................................................ 19
Gas Valve Pressure Regulator Adjustment .................... 19
Adjustment Procedure for Parallel Valves ................. 20
Check Manifold Pressure at Minimum Rate ............. 20
Combustion Testing ..................................................... 21
Verify Input Rate .......................................................... 21
Check CO2, CO and Stack Temperature ..................... 21
Cleaning Heat Exchanger (Models 032-020) ............... 21
Cleaning Heat Exchanger (Models 020-025) ............... 22
Leakage Symptoms ....................................................... 22
Checking for Leaks ....................................................... 23
Causes of Failures ......................................................... 23
Replacing Heat Exchanger ............................................ 23
Furnace Condensation .................................................. 24
Rear Cleanout Port ....................................................... 24
Combination Fan and Limit Control ........................... 25
Maintenance
Monthly, Twice Yearly, Yearly ..................................... 25
Troubleshooting Guide ............................................. 26
Typical Parts List – 60 Hz ....................................... 28
Capacities & Adjustments Table ............................ 29
Performance & Service History ............................ 30
SERVICED BY:
TELEPHONE NO: INSTALLATION DATE:
Installer: Leave this manual with owner. It is to be posted and maintained in legible condition.
Page 2 / IM 685
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 20 to 1 turndown ratio. 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.
Units equipped with gas heating must not be operated in an atmosphere contaminated with
chemicals which will corrode the unit such as halogenated hydrocarbons, chlorine, cleaning
solvents, refrigerants, swimming 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 constitutes product abuse and will void all warranty
coverage by the manufacturer. Questions regarding specific contaminants should be referred to
the appropriate local gas utility.
Ventilation and 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 CO2 and CO at several firing rates. 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.
IM 685 / Page 3
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 and all required parts, including fasteners, are
furnished and shipped inside the burner vestibule of the unit. On Models 150 through 200, the flue box
and hardware 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 ➁ in the casing of the unit that line up with the bottom lip holes of the flue box
tube sheet ➂. 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 ➂, attaching top to roof dam strip with screws ➀. 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 ➂ 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 √ , being careful not to obstruct the square drain holes in each front corner.
Three ounce tubes of silicone sealant are included in the envelope which also contains the electrical
schematics, etc. Models 020-100 are shipped with one tube and Models 110-200 are shipped with
two tubes.
4. Install flue box wrapper sheet √ by sliding it up from below so as not to disturb the silicone seal
described in 3 above. Attach with side screws ➄. At this time reinstall bottom screws ➁.
Figure 1. Flue Box
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).
Page 4 / IM 685
Figure 2. Wind Deflector (Models 032 thru 140)
➂
√
Electrical
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
through 200 furnaces require reassembly of some electrical connections as the burner is removed for
shipment.
Improper installation, adjustment, alteration, service or maintenance can cause injury or property
damage. Refer to installation and maintenance information provided with this furnace. For
assistance or additional information, consult a qualified installer, service agency or the gas
supplier.
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 Board of Fire Underwriters’ Pamphlet No. 54 or the
National Fuel Gas Code (ANSI Z223.1), and any applicable local codes.
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.
IM 685 / Page 5
Valve and 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.
Table 1. Capacity of Pipe Natural Gas (CFH)
WITH PRESSURE DROP OF 0.3" 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
Note: Use multiplier below for other specific gravities and pressure drops.
1
⁄2
3
⁄4 11
PIPE SIZE–INCHES (IPS)
1
⁄4 1
1
⁄2 22
1
⁄2 34
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 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
Page 6 / IM 685
Gas Piping Routing Into Unit
On-the-Roof Piping (Models 020 thru 140)
1. Remove knockout ➀ at corner of burner vestibule door and saw out corner of door. See Figure 3b.
Make saw cuts ➁ tangent to round hole and square with door edges.
2. Install pipe corner plate ➂ on vestibule, locating on pre-punched 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 thru 140)
1. Remove bottom access panel ➄. See Figure 3c.
2. Remove knockout √ and make an opening ≈ through bottom deck directly below knockout hole.
3. Route gas pipeline through these openings and seal them off with suitable grommets ∆. See Figure
3a Section A-A.
4. Replace bottom access panel ➄.
Figure 3a. Figure 3c.
Figure 3b.
Typical Piping Connections
Figure 4
Figure 4b. Figure 4a.
With Shutoff Cock Folded Back
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.
With Shutoff Cock in Front
IM 685 / Page 7
Figure 5.
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 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 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 require, 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 sheetmetal 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.
Page 8 / IM 685
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 start-up to receive instructions in the operation,
care and adjustment of the unit.
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, monometer 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, CO2 indicator, carbon monoxide 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 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 LS1 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.
IM 685 / Page 9
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 be used to control the amount of heating. Set the control system to call for heat so OBA3
energizes Relay R20. With OBA3 closed, vary the temperature control set point to increase, maintain,
or reduce the firing rate of the burner as required for these tests. If OBA4 is closed the firing rate will
decrease. If OBA5 is closed the firing rate will increase. If neither are "made" the firing rate will remain
unchanged.
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 CCW 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.
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 the 1⁄8 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 (4), Figure 16b. The 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 measure the burner air box pressure at port (4), Figure 16b. 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 the burner. These problems could include linkages
disturbed during shipment, etc.
Page 10 / IM 685
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