Cambridge Engineering, Inc.
30
M-Series Technical Manual
c1. To change the profile plate pressure drop on
model M110 - M115 heaters with a Manual
Profile Adjust mechanism, locate the adjust-
ing mechanism in the electrical control enclo-
sure, loosen the lock-down bolt, and rotate the
adjuster to increase or decrease the pressure
as required. Retighten the lock-down bolt to
secure the mechanism.
c2. To change the profile plate pressure drop on
model M118 - M140 heaters with a Manual
Profile Adjust mechanism, locate the adjusting
mechanism in the gas train enclosure, loosen
the jam nut, and rotate the adjusting nut to
increase or decrease the pressure drops, as re-
quired. Hold the adjusting nut and retighten the
jam nut to secure the mechanism.
c3. For make-up air heaters with an Automatic
Profile Adjust system, check the Differential
Pressure Switch/Gauge and verify that the left
orange needle is set to the Minimum setting and
the right orange needle is set to the Maximum
setting from the table above.
IMPORTANT
Call the Cambridge Engineering Customer Service
Group at 800-473-4569 if unable to obtain the required
pressure drop across the burner profile plate.
o
6. MOTOR AMP DRAW CHECK
IMPORTANT
The heater access doors must be closed for this test.
a. Check the motor current at the overload relay
on all three legs.
b. Turn the blower service switch to the “OFF”
position.
IMPORTANT
The average amps must not exceed the motor nameplate
FLA. High amperage may indicate excessive blower
RPM. Call the Cambridge Engineering Customer
Service Group at 800-473-4569 if unable to obtain ac-
ceptable amperage readings.
o
7. CALCULATING AND ADJUSTING BURNER
MANIFOLD PRESSURE
a. Turn the disconnect switch off.
b. Disconnect #3 wire from the amplifier to drive the
modulating valve to full open.
c. If the ambient temperature is at or above the
Entering Air Thermostat (EAT) setpoint on
the multi-functional PC board, then note the
setpoint position and set the EAT to its highest
