M-Series Technical Manual
35
Cambridge Air Solutions
f. Verify that the minimum fire flame signal
is steady and above 2.0 microamps (
m
A).
IMPORTANT
If any of the conditions in steps 10.e and 10. f are not
met, an adjustment is required.
g. Minimum Fire Adjustment
i. On M511 or M611 modulating
valves, to adjust the minimum
fire, remove cap (A) exposing the
minimum fire adjusting screw. On
the MR212 modulating/regulating
valve, remove the housing cover,
then cap (A), and then loosen lock
screw (C). Turn the adjusting screw
(B) to obtain the desired minimum
fire setting. A clockwise rotation
decreases the flame size and reduces
minimum flow rate. Repeat steps
10.e and 10.f.
Modulator
ii. Replace the cap (A). Tighten the lock
screw (C) on the MR212 valve prior
to reinstalling the cap and housing
cover.
iii. Turn the blower and burner service
switches to the
“
OFF
”
position.
iv.1. For units with an A1014 or an A1044
amplifier: Reinstall the #8 wire on
the amplifier that was removed in
Step 10.d.1 (See page 34).
iv.2. For units with an SC25S signal
conditioner: Reinstall the push on for
terminal #3 on the signal conditioner
that was removed in Step 10.d.2 (See
page 34).
v. Remove the meter and reattach the red
wire to terminal FP on the FSR board.
11. LOW FIRE START ADJUSTMENT
The Low Fire Start control setting is preset at the
factory to provide a fixed, repetitive, initial firing
rate that equates to the following for most burner
applications:
• 20˚F to 30˚F temperature rise
• 0.10 to 0.30 inches WC manifold differential
pressure (above blower pressure)
• Voltage to the modulating valve of 9 to 11 Volts
DC for the Maxitrol M511 or M611 valve and 10
to 13 Volts DC for the Maxitrol MR212 valve.
• Flame length of 3" to 5"
The Low Fire Start function lasts for 15 seconds
before returning to the control of the temperature
control system. It is important that the flame travels
across the burner length fast enough (within 2
seconds) to establish the flame signal during the trial for
ignition period. If adjustment is required, proceed as
follows:
a. Connect a meter in the flame sense circuit
as in step 10.b (page 34).
b. Connect a manometer to the burner static
pressure port. Turn the blower service
switch to the “LOCAL” position and
the burner service switch to the “OFF”
position and measure the burner static
pressure.
c. Connect a DC voltmeter to terminals “MV
OUT” on the multi-functional PC board.
d. Turn the burner service switch to the
“
LOCAL
”
position and monitor the
modulating valve voltage, flame length,
manifold differential pressure, and the time
required to establish flame signal after the
gas valves are energized. (This may need
to be repeated several times to note all of
the above information)
e. If adjustment is required, the Low Fire
Start adjustment screw is located on the
multi-functional PC board as shown in
the drawing. Only minor adjustments are
normally required to obtain the proper
setting.
