M-Series Technical Manual
77
Cambridge Engineering, Inc.
TROUBLESHOOTING GUIDE
Problem
Possible Cause
Corrective Action
VIII. MODULATING
VALVE DOES NOT
MODULATE;
CONTINUOUS
HIGH FIRE
(Continued)
4. Space thermostat (Series 14 only)
a) Thermostat out of calibration
b) Thermostat located improperly
c) Thermostat differential setting too wide
d) Thermostat defective
a) Recalibrate thermostat or replace.
b) Thermostat in cold draft - relocate.
c) Reduce differential setting.
d) Replace thermostat.
5. Remote Heat Adjust (TD114)
a) Short in Remote Heat Adjust circuit
b) Induced voltage in field wiring
a) Replace Remote Heat Adjust if resistance
measure between terminals 1 and 3 of
Remote Heat Adjust is less than 6,000 Ω.
b) Utilize shielded, twisted pair wiring.
6. Modulating Valve (M511, M611 or
MR212)
a) Foreign material holding valve open
b) Modulating valve misassembled
a) Disassemble valve and remove foreign
material.
b) Disassemble valve and assemble correctly
IX. MODULATING VALVE
DOES NOT
MODULATE;
CONTINUOUS
LOW FIRE
1. Class II Transformer
a) No voltage output to amplifier
a1) Check for short in modulating valve coil.
a2) Replace transformer.
2. Modulating Valve
a) Valve coil is open or shorted
b) Plunger jammed
c) Ruptured main or balancing diaphragm
a) Replace valve coil if its resistance is less
than 40 Ω or greater than 85 Ω.
b) Clean or replace plunger.
c) Check diaphragm condition and replace if
defective.
3. Amplifier
a) No output voltage to valve
a) With the wire removed from terminal 3
of amplifier, replace amplifier if the valve
voltage does not exceed 18 Volts DC.
4. Discharge Temperature Sensor
(TS114 or TS144)
a) Short in sensor circuit
b) Temperature control system out of cali-
bration
a) Replace the sensor if the resistance mea-
sured at: terminals 1 and 2 on TS114 is
less than 8,000 Ω; terminals 1 and 3 or 2
and 3 on TS144 is less than 2,900 Ω.
b) Perform temperature control system cali-
bration.
