IM 685 / Page 9
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, CO
2
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.
