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TROUBLESHOOTING GUIDE
TROUBLESHOOTING GUIDE
Modulating Room Temperature (MRT, MRT-PRO or MRT-EXPERT) Controls
Portions reproduced with permission from Maxitrol
®
Company
Symptom
Possible Cause
Field Test
Remedy
1. Install properly.
1. If proper resistance values
are not observed, replace
modulator head or repair
wiring.
2. Clean or replace plunger if
necessary.
3. Replace diaphragm if
ruptured.
1. Prove the power source.
2. Correct the wiring.
3. If item B1 checks out and
modulating voltages are
still not obtained, ampli
fi
er
(RE-26) may be assumed
faulty. Replace.
4. Contact Factory.
1. Adjust to proper low
fi
re.
2. If greater than 1.5" negative
pressure, check equipment
for clogged
fi
lters and other
inlet air restrictions. For other
solutions, consult factory.
1a. Replace Sensors if reading is
incorrect or correct wiring.
1b. Change to correct setpoint.
1c. Change to correct setpoint.
1. Change to correct setpoints.
A. No Gas Flow with
DO-2 on UC-01
energized.
B. Continuous Low
Fire (Electronics
OK).
C. Continuous Low
Fire (Electronics
Problem).
D. Incorrect
Low Fire.
E. Continuous
Minimum
Discharge Air
Temperature.
F. Incorrect
Maximum
or Minimum
Discharge Air
Temperature.
Control circuits external to MRT Controls can cause burner malfunction.
Always check manual valve to be certain gas is on, and check limit controls for normal operation.
1. Arrow on side of valve
should point in direction
of gas
fl
ow.
1. Remove wires connected
to ampli
fi
er terminals and
measure resistance. MR212
(60-80 ohms),
M611 (45-55 ohms).
2. Inspect - plunger should be
installed to operate freely in
solenoid sleeve.
3. Disassemble valve for
inspection of internal parts.
1. Check for 24V AC at
ampli
fi
er (RE-26) terminals
7 & 8.
2. Inspect.
3. Check item B1. Check
for 2-10 VDC input signal
from (UC-01) at terminals
1 & 2. Check for 0-20 VDC
output signal to gas valve at
terminals 5 & 6.
4. Check DC Voltage on AO-1.
1. See Valve Adjustments
Section X.
2. Close main gas supply and
measure manifold pressure
with blower operating.
Should be less than 1.5" w.c.
negative pressure.
1a. Check Outside Air Sensor
(TS-01),Space Temperature
Sensor (TS-02) and
Discharge Air Sensor
(TS-03) for correct readings.
See Thermistor curve.
1b. Check Space Temperature
Sensor (TS-02) setpoint.
1c. Check Heating Occupied
and/or Unoccupied setpoint.
1. Install a BACview 6 or PC.
1. Valve improperly
installed.
1. Open circuit in
modulator coil.
2. Plunger missing,
jammed or improperly
installed.
3. Ruptured main or
balancing diaphragm.
1. Short circuit or no
voltage to the ampli
fi
er
(RE-26).
2. Jumper not connected
across ampli
fi
er (RE-26)
terminals 3 & 4.
3. Faulty ampli
fi
er (RE-26).
4. No output voltage on
UC-01.
1. Incorrect by-pass metering
valve adjustment.
2. Excessive negative
burner pressure.
1. Incorrect room
temperature.
1. Maximum or minimum
heating discharge
temperature setpoint
not set correctly.
(Refer to Digital Control System User Manual for additional troubleshooting suggestions)
