Cambridge Air Solutions.
42
M-Series Technical Manual
IMPORTANT
If any of the conditions in steps 10.f and 10.g are not
met, an adjustment is required. Please refer to drawing
below.
h. Minimum Fire Adjustment
i. To adjust the minimum fire on a maxitrol
M411, M511 or M611, 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. Repeat steps 11.e and
11.f until a consistent flame signal of 2-5uA or above is
observed.
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.
12. GAS VALVE LEAK CHECK
All heaters should be evaluated for the gas tightness
of the gas valve seat. Heaters with separate redundant
valves are equipped with a leak test facility to assist in
checking this seal. A momentary switch and a gas port
for measuring pressure between valves are provided
as the leak test hardware. Refer to the Individual
Component Description Section in the Technical Manual
for more information regarding the leak test switch. The
procedures for the gas valve leak check are as follows:
a. Connect a 0 to 10 inches water column
(inch WC) manometer to the 1/8" NPT
tapped fitting on the manual shut-off
valve located just prior to the burner for
the purpose of monitoring an increase in
pressure. Verify that the manometer is
properly zeroed.
b.1. On single redundant valve applications
(heaters rated less than 400,000 Btu/
hr), close the manual burner shut-off
valve and wait 30 seconds to read the
manometer. If the reading is greater than 0
inch WC, replace the gas valve and retest.
If the reading is 0 inch WC, remove the
manometer and reinstall the pipe plug.
b.2. On heaters with separate redundant valves,
close the manual burner shutoff valve,
hold the momentary leak test switch in
the closed position, and wait 30 seconds
to read the manometer. If the reading
is greater than 0 inch WC, refer to the
Maintenance Instruction Section for
information on Gas Valve Cleaning for
cleaning the second gas valve and retest.
If the reading is 0 inch WC, remove the
manometer and reinstall the pipe plug.
c. To check the gas tightness of the first
valve in the gas train on heaters with
separate redundant valves, connect the
manometer to the leak test port between
the valves and verify that the manometer
is properly zeroed. Wait 30 seconds
to read the manometer. If the reading
is greater than 0 inch WC, refer to the
Maintenance Instruction Section in the
Technical Manual for information on Gas
Valve Cleaning for the first gas valve and
retest. If the reading is 0 inch WC, remove
the manometer and reinstall the pipe plug.
13. GAS TRAIN LEAK CHECK
a. Turn the blower and burner service
switches to the “LOCAL” position.
b. With the burner operating, spray the
complete gas train with leak detector
solution, checking all pipe connections
and plugs.
c. Turn the blower and burner service
switches to the “REMOTE” position.
14. PRELIMINARY REMOTE CONTROL STATION
OPERATIONAL CHECK
a. Turn the blower and burner service
switches to the “REMOTE” position and,
if applicable, turn the Remote Control
Station mode selector switch to the
“HEATING” position.
b. Identify the type of Remote Control
Station, if applicable, that is utilized on
this application.
Refer to Individual Component Description Section for
additional information.
