M-Series Technical Manual
29
Cambridge Engineering, Inc.
of the disconnect switch. For model M118 - M140
heaters, check the electrical supply voltage at the
disconnect switch.
m
CAUTION:
Do not proceed with start-up unless the supply
voltage agrees with the nameplate voltage. If the
supply voltage does not agree with the name-
plate voltage, check with your local Cambridge
Engineering representative or Cambridge
Engineering’s Customer Service Group at 800-
473-4569 to determine what changes are required.
3. GAS SUPPLY PRESSURE VERIFICATION
Verify that the gas supply pressure complies with the
heater nameplate.
m
CAUTION:
Do not proceed with start-up unless the gas sup-
ply pressure agrees with the nameplate pressure
requirements. If the gas supply pressure is in
excess of the maximum pressure indicated, a sepa-
rate positive shut-off high pressure regulator must
be added upstream of the heater’s individual low
pressure manual shut-off valve. If a high pressure
regulator is needed and has not been installed,
check with your local Cambridge Engineering rep-
resentative or Cambridge Engineering’s Customer
Service Group at 800-473-4569 to determine the
size and capacity requirements that are required.
4. BLOWER ROTATION CHECK
a. Open the access door on the electrical control enclosure
side and turn the disconnect switch on.
m
WARNING:
When the disconnect switch is activated with the
enclosure open, live power is present. Only experi-
enced technicians with knowledge and respect for
live power should proceed beyond this point.
b. Turn the blower service switch to the
“
LOCAL
”
position. The blower motor will start after the
motorized inlet damper opens. Then turn the
blower service switch to the
“
OFF
”
position and
verify the blower is rotating in the proper direction.
(See the directional arrow on the blower housing.)
IMPORTANT
On a three phase system, the rotation direction of the
blower may be reversed by switching any two wires lo-
cated on the downstream side of the service disconnect.
The electrical supply to the heater must be turned off
prior to switching the wiring.
IMPORTANT
Indications of loose belts include barking or squeal-
ing when the blower starts. If these symptoms occur,
please refer to the BELT TENSIONING section of
the MAINTENANCE INSTRUCTIONS (see page 59).
Periodic belt adjustments may be required.
5. BURNER PROFILE DAMPER PRESSURE
DROP CHECK
IMPORTANT
The blower access doors must be in place when adjust-
ing the profile plate.
IMPORTANT
Verify that the inclined manometer, if applicable, is
level and zeroed for proper readings to be obtained.
a. Turn the blower service switch to the “LOCAL”
position. (Note: The burner service switch must
remain in the “OFF” position)
b. Check the pressure drop across the burner profile
plate to ensure that it complies with the table
below:
Profile Plate Pressure Drop -
Blower Only
(inches WC)
Gas
Type
Models
Filters Manual
Adjust
Automatic
Adjust
Min. Max.
Nat-
ural
M110-M140
No
0.68
0.62 0.72
M110-M136
Yes
0.72
M140
Yes
0.75
LP
M110-M140
No
0.90
0.84 0.94
M110-M136
Yes
0.94
M140
Yes
0.97
