Cambridge Engineering, Inc.
76
M-Series Technical Manual
TROUBLESHOOTING GUIDE
Problem
Possible Cause
Corrective Action
VI. HIGH LIMIT TRIPPED
1. High Limit
a) High limit will not reset
a) Replace high limit.
2. Burner Overfiring
a) Manifold pressure too high
a) Adjust manifold pressure regulator to
obtain temperature rise specified on heater
nameplate.
3. Discharge Damper
a) Damper blades partially closed
b) Defective damper motor
a) Adjust damper stroke length.
b) Replace damper motor.
4. Low Airflow
a) Blower running backwards
b) Belts slipping
c) Blocked intake or discharge
a) Reverse motor direction.
b) Tighten or replace belts.
c) Find and remove obstruction
5. Temperature Control System
a) Temperature control system does not
modulate
a) See problem VIII for Electronic Discharge
Control systems.
VII. BLOWER RUNS;
UNIT HEATS;
WILL NOT CYCLE
OFF
1. Operating Thermostat
a) Short in thermistor circuit
b) Thermostat located improperly
c) Thermostat differential setting too wide
d) Defective thermostat
a) Check thermistor wiring and/or replace
thermistor.
b1) Thermostat in cold draft-relocate.
b2) Thermostat not satisfied-turn down
c) Reduce differential setting.
d) Replace thermostat.
2. Burner Service Switch
a) Switch in LOCAL position
a) Place switch in REMOTE position.
3. Auxiliary Control
a) Auxiliary contacts closed
a) Check auxiliary circuit wiring and
contacts
4. Misunderstood Control System
Operation
a) Control system doesn’t function as
expected
a) Review control system operational charac-
teristics.
VIII. MODULATING
VALVE DOES NOT
MODULATE;
CONTINUOUS
HIGH FIRE
1. Amplifier (A1014 or A1044)
a) Wire not connected to amplifier terminal
3 or 4.
b) Jumper not installed between terminals 2
and 3 of A1014 amplifier only.
c) Defective amplifier
a) Reinstall wire.
b) Reinstall jumper.
c) Replace amplifier.
2. Discharge Temperature Sensor
(TS114 or TS144)
a) Open in sensor circuit
b) Sensor cross-wired to amplifier
a) Replace the sensor if the resistance mea-
sured at terminals 1 and 2 on TS114 sen-
sor exceeds 11,000 Ω; terminals 1 and 3
or 2 and 3 onTS144 exceeds 6,000Ω.
c) Correct wiring terminations.
3. Space Temperature Selector
(Series 44 only) (T244 or TS244/TD244)
a) Open in sensor circuit
b) Induced voltage in field wiring
c) Space sensor located improperly
a) Replace the sensor if the resistance mea-
sured is more than: 7,000 Ω for the T244;
5,500 Ω for the TS244; or 2,250 Ω for the
TD244.
b) Utilize shielded, twisted pair wiring
c) Sensor in cold draft - relocate
