M-Series Technical Manual
67
Cambridge Engineering, Inc.
DAMPER MOTOR
The damper motor operates on 24
Volts AC and transmits power to
the motor starter when the damp-
er blades are fully open by the
closure of the damper end switch.
The damper end switch is an
adjustable internal auxiliary
switch which has been factory set to operate when the
damper is fully open. The damper motor will power closed
when the heater cycles off. The damper motor will not
close unless the blower service switch is in the
“
REMOTE
”
position. Refer to detailed instructions
regarding the replacement and adjustment of the damper
motor (see page 53).
DISCHARGE TEMPERATURE SENSOR
The discharge temperature sensor is
mounted on the fan housing and is a
component of the Maxitrol Series 14
and Series 44 temperature control sys-
tems. It senses the average fan dis-
charge temperature and transmits a
resistance signal back to the ampli-
fier that corresponds to the dis-
charge temperature. The Maxitrol
Series 44 and Maxitrol Series 44/Tamperproof tempera-
ture control systems use the Maxitrol Series 44 sensor
(TS144). The Maxitrol Series 14 control systems use the
Maxitrol Series 14 sensor (TS114).
DISCONNECT SWITCH
The non-fused disconnect switch
is provided on all heaters and
includes a lockable operating
knob. The disconnect must be off
before accessing the electrical con-
trol enclosure. Once the control enclo-
sure is open, experienced service
technicians may activate the electrical circuit to assist in trou-
bleshooting.
EXHAUST FAN CONTACT
The exhaust fan contact is an auxiliary dry contact that
is mechanically interlocked to operation of the heater’s
motor starter and is provided with terminals located in
heater’s electrical enclosure. The dry contact is typically
wired into an exhaust fan control circuit to activate the
exhaust fan as a slave to the make-up air heater.
FLAME SAFEGUARD RELAY
The flame safeguard relay supplies
24 Volts AC to the igniter for 4
seconds prior to the gas valve
being energized. If the burner
does not light (flame is not estab-
lished within 7 seconds), this control
will lock out. If flame signal is lost
during burner operation, the control will allow one retry
for ignition.
FLAME ROD
The flame rod senses the pres-
ence of flame, and signals the
flame safeguard relay. The pres-
ence of flame is detected by the
flame rectification of the AC sig-
nal that is supplied to the flame
rod, thus creating the DC response. The resulting current
flow produced can be measured with a DC microamme-
ter. The reading should be steady and between 2.0 and
6.0 microamps (
m
A).
FUSE BLOCK
The fuse block provides line fusing for
branch circuit protection. It is wired in
conjunction with the non-fused discon-
nect switch.
HIGH GAS PRESSURE SWITCH
The high gas pressure switch is a manual reset
safety device to lock out the burner operation
should large gas pressure fluctuations
occur. The high gas pressure switch
should be set at 25% above manifold gas
pressure. The adjustment screw is located
under the top plate.
HIGH PRESSURE REGULATOR
The high pressure regulator is required
when the gas supply pressure exceeds
the nameplate rating for the heater.
The high pressure regulator assembly
is also furnished with a high gas pres-
sure manual shut-off valve and a tap for
measuring the upstream gas pressure. The high pressure
regulator is a positive lock-up type regulator which must
be vented to the outdoors. It is sized according to the gas
supply pressure and the capacity requirements of the heater.
