Installation and Maintenance Manual SuperMod Forced Draft Gas Fired Furnace on McQuay Applied Rooftop Systems IM 685-2 Group: Applied Systems TM Part Number: IM685 Date: February 2007 HT***A* with RM7897A Flame Safeguard © 2007 McQuay International IM 685-2 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. Table of Contents General Warranty Exclusion .............................
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.
Figure 1. Flue Box 1 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.
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.
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.
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.
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” on page 17. 2. The furnace must not operate at an airflow below the specified Minimum Airflow CFM.
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.
Combustion Tests These tests should be run when the furnace is at normal operating temperature (after the furnace has been running 10 to 15 minutes), and should be run at several firing rates including maximum and minimum. Cycle the Unit Cycle the unit through several start-ups with the temperature controls calling for first minimum rates and finally maximum rates. Be alert for any hints of trouble or unexplained inconsistencies that could indicate future problems. a.
Typical Sequence of Operation When the rooftop unit is energized 120 volt power is supplied to the system on/off switch (S1), to burner on/off switch (S3) and 24 volts to the (BO#11) contacts on the main control board (MCB). Note: On field supplied controls, 120V power is supplied through the system on/off switch (S1) to burner on/off switch (S3) and to the field supplied gas heat on/off contacts.
Flame Safeguard See manufacturer's bulletin for more detailed information on flame safeguard RM7897A. The Honeywell RM7897A is a microprocessor based integrated burner control that will perform self-diagnostics, troubleshooting, and status indication, as well as the burner sequencing and flame supervision. Keyboard Display Module The Honeywell S7800A1001 module is an optional device available for use with the RM7897A.
Service General Before starting service on this burner take the time to read the sections “About This Burner” on page 8 and “Typical Sequence of Operation” on page 11 to get an overview. Gun Assembly The McQuay gas burner gun assembly is easily removable and includes the ignition electrode assembly, the flame rod assembly, and a “Base Air” fitting with orifice. The positioning of this assembly is not considered field adjustable.
Air and Gas Adjustments The burner has been adjusted and tested at the factory with accurate instruments. There should not be a need to readjust the burner after the unit has been installed. Verify that the gas supply pressure is correct, the electrical power is correct, and test the burner thoroughly. Do no make adjustments unless there is a clear indication that there is a problem, and proper instruments are available so the adjustments can be made correctly.
Grasp the rod and while applying some thrust to the rod in the direction of the actuator to take up any free play, and with the bracket in alignment with the linkages that connect to it, tighten the two set screws. Return the actuator to the minimum rate position. The adjustable plate (2) in Figure 10 is positioned to provide an opening per dimension “F.” Figure 10.
Gas Valve Pressure Regulator Adjustment The high turndown burner uses combination gas controls to provide redundant on-off gas control and pressure regulation. A burner will have from one to six of these controls piped in parallel depending on the BTU rating of the burner. When two or more valves are in parallel their pressure regulators must be adjusted so the valves maintain the specified manifold pressure and are balanced so each valve handles its share of the load.
Generally a valve will he found that has an effect, and very little adjustment will cause a reduction in the minimum rate manifold pressure. Reduce the pressure adjustment of that dominant valve by slowly rotating the adjuster CCW until the manifold pressure no longer drops in response to that adjuster movement.
Models 020 thru 025 (see Figure 14) 1. To gain access to the inside of the combustion chamber, detach the burner from the furnace and set it on the floor of the vestibule (see Figure 14, Item (3)). The burner is attached to the furnace studs with four nuts. Conduit lengths allows this movement of the burner without disconnecting wiring. The union on the gas line must be opened. 2. Remove the flue box front wrap (1). 3. Remove and clean the turbulator (2) from each tube and clean the flue box. 4.
3. Excessive Condensation - Applications which will produce condensation require an all stainless steel heat exchanger that is resistant to the effects of this condensation and that will give long heat exchanger life. The likelihood of condensation increases with: a. Colder supply air temperature across the secondary tubes, as on units taking in a lot of outdoor air in colder weather. b. Lower heat flow through the secondary tubes, as on modulating burners when operating at reduced input. c.
Combination Fan And Limit Control The fan limit control is a hydraulic action type with a remote sensing element and connecting capillary tube. The sensing element is locked into a bracket located on one of the heat exchanger tubes about halfway toward the back of the furnace, on the side away from the blower. One corner of the bracket is bent aside to remove the element. Yearly 1. Gas Train - Check all valves, piping, and connections for leakage. Remove burner gun assembly.
Operation Initiate Period: When the relay module is powered it goes through a 10 second “Initiate” period. It will also enter into the “Initiate” period if electrical power problems such as low voltage or momentary interruption occur while the unit is operating. Operation of the burner fan motor is delayed throughout the “Initiate” period. Standby: After the initiate period is completed, the module will enter the standby mode and await a call for heat by the temperature control system.
Troubleshooting Chart The RM7897A flame safeguard is equipped with an LED to aid in the diagnosis of burner operation and problems. Fault identification is a series of fast- and slow-blinking LED lights. The fast blinks identify the tens portion of the fault code (two fast blinks is 20), while the slow blinks identify the units portion of the fault code (two slow blinks is 2). Two fast blinks followed by two slow blinks would be fault code 22.
MOTOR RUNS, PILOT IGNITES... a. Check Table 6. The LED code may diagnose the problem. 3.1 Burner motor starts. After 30 (60 or 90) seconds the PILOT LED comes on, the FLAME LED comes on momentarily and then goes out. b. The power is only momentarily proving itself to the flame safeguard. It must be proven at the end of the of the 10 second ignition trial. c. On a new start-up, this could indicate the gas lines have not been sufficiently purged of air. d. Improper flame rod position. e.
Table 6. Fault codes BLINKING FAULT CODES... Fault Code System Failure Code 1-1 *Low AC Line Low AC Line detected. Voltage* Code 1-2 *AC Quality Problem* Excessive noise or device running on slow, fast, or AC line dropout a. Check the relay module and display module connections. b. Reset and sequence the Relay Module. c. Check the 7800 power supply and make sure that frequency and voltage meet specifications. d. Check the backup power supply, as appropriate. detected. a.
a. Make sure the purge card is seated properly. Code 4-1 *Purge Card Problem* No purge card or the b. Inspect the purge card and the connector on the relay module for any damage or contaminants. purge card timing has c. Reset and sequence the relay module. changed from the d. If the fault code reappears, replace the purge card. original configuration. e. Reset and sequence the relay module. f. If the fault code persists, replace the relay module.
Typical Parts List - 60 Hz QTY. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 1 1 1 2 1 1 1 1 1 1—6 1 1 1 1 26 MCQUAY PART NO.
IM 685-2 (2) (3) 250 312 400 500 625 800 812 1000 1000 1250 1375 1750 1875 2500 @ Max. Rate 12.5 15.6 20.0 25.0 31.3 40.0 40.6 50.0 50.0 62.5 68.8 87.5 93.8 125.0 Note 4 @ Min. Rate Note 3 Input MBH or CFH 2,300 3,800 2,950 6,000 4,600 9,600 5,970 12,000 7,340 15,000 10,100 21,000 13,700 30,000 (5) 80 61 100 61 100 61 100 61 100 61 100 61 100 61 Max. TR Deg F Furnace Min. CFM (4) Key: (1) Gas Manifold Pressure Tap (1/8 inch l.P.) (2) Gas Line Pressure Tap (1/8 inch l.P.
Reference Number: (1) Initial Startup of Furnace 27 28 (1) * Tap Locations are shown as (2) and (9) on Figure 16. (Summarize any service work performed) Comments Flue Gas CO (PPM) Air Pressure in Box (In. W.C.) Gas Manifold Pressure (In. W.C.)* Gas Line Pressure (In. W.C.)* Flame Signal (DC Volts) Ambient Temperature (Deg. F) Flue Gas Temperature (Deg. F) Flue Gas CO2 (percent) Flue Gas CO (PPM) Air Pressure in Box (In. W.C.) Gas Manifold Pressure (In. W.C.)* Gas Line Pressure (In. W.C.
McQuay Training and Development Now that you have made an investment in modern, efficient McQuay equipment, its care should be a high priority. For training information on all McQuay HVAC products, please visit us at www.mcquay.com and click on training, or call 540-248-9646 and ask for the Training Department. Warranty All McQuay equipment is sold pursuant to its standard terms and conditions of sale, including Limited Product Warranty. Consult your local McQuay Representative for warranty details.
