MUA-SVX01A-EN • Direct-Fired Make-up Air
87
Trouble Shooting
2. Continuous low fire
(electronics problem).
No voltage to the
amplifier.
Check for 24V AC at
amplifier terminals 8 & 9.
a. Provide 24V
AC to the
amplifier.
Short in modulator coil
circuit.
Measure resistance in
modulator coil.
a. If proper
resistance
values are not
observed,
replace the
modulator
head or repair
wiring.
Short circuit in
discharge air sensor
circuit or wiring.
Remove wires connected
to amplifier terminals 1, 2
& 3. Measure resistance
across wires 1 & 3, then 2
& 3. Meter should read
greater than 2500 ohms.
a. If readings
are incorrect,
replace the
discharge air
sensor or
repair the
wiring.
Faulty amplifier.
Follow procedures
outlined in the
a. If power
source and
modulator coil
check out, but
proper
modulating
voltages
cannot be
obtained, then
amplifier may
be assumed at
fault. Install
replacement
amplifier.
3. Continuous low fire
(electronics ok).
Open circuit in
modulator coil.
Remove wires connected
to amplifier terminals 6 &
7 and measure
resistance. MR212 (60-80
ohms), M611 (45-55
ohms).
a. If proper
resistance
values are not
observed,
replace
modulator
head or repair
wiring.
Ruptured main or
balancing diaphragm.
Disassemble valve for
inspection of internal
parts.
a. Replace
diaphragm if
ruptured.
Plunger missing,
jammed or improperly
installed.
Inspect. Plunger should
be installed to operate
freely in solenoid sleeve.
a. Clean or
replace
plunger if
necessary.
4. Incorrect low fire.
Incorrect bypass
metering valve
adjustment.
a. adjust to
proper low fire.
Table 18.
Trouble shooting guide for Modulationg Room Temperature (MRT)
controls
Symptom
Probable Cause
Field Test
Solution
*
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.
