M-Series Technical Manual
39
Cambridge Air Solutions
a. Document the nominal motor current
from parameter 9906 of the VFD. This
is the blower motor full load amps
(FLA). To access the VFD parameters,
press the “MENU” button on the VFD
keypad and use the arrows to scroll to
“PARAMETERS” and press “ENTER”.
Then scroll to group “99” and press
“ENTER”. Then use the arrows to scroll
to parameter 9906 to view.
b. Locate the “VFD SPEC’S” sticker located
on the subpanel to the right of the VFD
and document the “AMPS @ DESIGN”.
c. Document the actual “AMPS” from the
VFD display. The amps on the VFD
display should be within 10% of the
“AMPS @ DESIGN”.
d. If amps on VFD display are greater / less
than 10% of “AMPS @ DESIGN”, please
contact the Cambridge Customer Service
Group at 1-800-473-4569. In order for
the unit to operate at the specified CFM,
the High Speed amps need to be at the
“AMPS @ DESIGN”.
IMPORTANT
The average amps must not exceed the motor nameplate
FLA. High amperage may indicate excessive blower
RPM. Call the Cambridge Air Solutions Customer
Service Group at 800-473-4569 if unable to obtain
acceptable Amperage readings.
7. BURNER PROFILE DAMPER PRESSURE
CHECK – LOW SPEED
IMPORTANT
-Note: The burner service switch must remain in the
“OFF” position.
-Note: The VFD should still be in “HAND” mode.
a. Press the down arrow on the VFD keypad
and hold till the Hz reach the low speed
programmed in the VFD; the hertz will
stop at the programmed low speed hertz.
Document the low speed Hz read on the
VFD display.
b. Document the pressure read on the
photohelic gauge.
IMPORTANT
If the pressure on the photohelic gauge is less than
.62” (NG) or .84” (LP), please contact the Cambridge
Customer Service Group at 1-800-473-4569. If the low
speed pressure measured on the photohelic is too low,
the low speed airflow is inadequate and may cause
equipment resets or burner short cycling.
8. 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 11 to 14 VDC
• Flame length of 3" to 5"
• Flame signal of 3-5uA
The Low Fire Start function lasts for 15 seconds before
returning control to the temperature control system. It is
important that the flame travels across the burner length
fast enough (within 1 second) to establish the flame
signal during the trial for ignition period. If adjustment is
required, proceed as follows:
a. Connect a meter set to read DC micro
amps (A) in order to verify the minimum
fire flame signal during the adjustment
process. Connect the meter by removing
the red wire from terminal FP of the flame
safeguard relay (FSR) and attaching the
positive lead of the meter to terminal FP
and the negative lead to the red wire.
b. Verify the blower service switch is in the
“LOCAL” position and the burner service
switch is in the “OFF” position.
c. Connect a DC voltmeter to terminals “MV
OUT” on the multi-functional PC board.
d. Press and hold the “UP” arrow on the
VFD keypad and increase the Hz to 60
Hz (or the max programmed Hz. The max
Hz may have been changed in step 6.d in
order to reach the “AMPS @ DESIGN).
e. Place the burner service switch in the
“LOCAL” position. Once the burner fires,
monitor the voltage measured on the “MV
OUT” terminals of the multi-functional PC
board and the time required to establish
flame signal after the gas valves are
energized.
