M-Series Technical Manual
33
Cambridge Engineering, Inc.
. 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. Reconnect wire #8 to the amplifier.
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 sec-
onds) 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 (see page 33).
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” posi-
tion and measure the burner static pres-
sure.
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 modu-
lating 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 set-
ting.
12. PRELIMINARY REMOTE CONTROL
STATION OPERATIONAL CHECK
a. Turn the blower and burner service switches
to the “REMOTE” position and, if applica-
ble, turn the Remote Control Station mode
selector switch to the “HEATING” posi-
tion.
b. Identify the type of Remote Control Station,
if applicable, that is utilized on this appli-
cation. Refer to Individual Component
Description Section for additional infor-
mation.
c.1. If the Remote Control Station utilizes
a thermostat, refer to the Operating
Instructions for the Electronic Thermostat
(see page 65) or the TSS Controller (see
page 67) to set the thermostat at its high-
est setting.
c.2. If another device in the Remote Control
Station controls the operation of the heater,
activate this device.
