Greenheck VSU Installation, Operation And Maintenance Manual page 17

IMPORTANT
Setting the maximum firing rate during mild weather
conditions may cause the high limit to trip out during
extreme conditions requiring manual resetting.
Gas trains are equipped with either separate
regulators and modulating valves or with a combined
modulating valve.
Clockwise rotation increases the temperature rise,
counterclockwise rotation decreases the temperature
rise.
The minimum setting for the maximum firing rate
may be higher than required. This is acceptable. The
burner will modulate as needed.
Regulators and Modulating Valves
Remove cap to access
maximum firing rate
adjustment
Separate Regulator and Modulating Valves
Minimum firing
rate adjustment
Remove one wire to send the unit
Combined Modulating Regulator
®
NOTE
NOTE
NOTE
Remove one wire to
send the unit to the
minimum firing rate
Minimum
firing rate
adjustment
Maximum firing
rate adjustment
to the minimum firing rate
Set the Minimum Firing Rate
Disconnect and isolate one of the wires running to the
modulating valve to send the unit to its minimum firing
rate. Set the minimum firing rate by adjusting the needle
valve indicated.
After setting the minimum firing rate, shut off the pilot
to ensure that the flame safeguard can still read the
main flame signal. Reconnect the wire to the modulation
valve and open the pilot shut-off valve.
IMPORTANT
The proper minimum firing rate setting results in a
small ribbon of continuous flame which covers the
flame rod and runs across the entire burner.
IMPORTANT
Do not allow the disconnected wire to come in
contact with a potential ground. Damage to the
amplifier or transformer could result.
IMPORTANT
On units with a 42 inch or greater burner, the flame
safeguard will automatically shut off the pilot after the
burner has been ignited.
Gas trains are equipped with either separate
regulators and modulating valves or with a combined
modulating regulator.
Adjusting the maximum and minimum firing rate
requires the inlet air sensor to be set higher than the
outdoor air temperature in order to start the burner(s).
Once high and low fire have been set, the inlet air
sensor should be set to the desired temperature.
Counterclockwise rotation increases the minimum fire
rate setting, clockwise rotation decreases the setting.
NOTE
NOTE
NOTE
Model VSU Make-Up Air 17