84
Direct-Fired Make-up Air •
MUA-SVX01A-EN
Trouble Shooting
5. Incorrect minimum
fire erratic or pulsating
flame.
Incorrect by-pass
metering valve
adjustment.
See valve adjustments on
page 35.
a. adjust to
proper
minimum fire.
Excessive negative
burner pressure.
Close main gas supply,
and measure manifold
pressure with blower
operating. Reading should
be less than 1.5" w.c.
negative pressure.
a. If reading is
greater than
1.5" negative
pressure,
check for
clogged filters
or other inlet
air restrictions.
Consult factory
for other
solutions.
6. Continuous high fire
(electronics ok).
Foreign object holding
valve open.
Remove bottom plate and
inspect valve and seat.
a. Clean seat.
Clean valve or
replace if
necessary.
Plunger jammed.
Inspect. Plunger should
be smooth and clean and
operate freely in solenoid
sleeve.
a. Clean or
replace
plunger.
7. Incorrect maximum
fire.
Inlet pressure too low.
Read pressure at inlet to
modulating valve using a
manometer with unit
operating at full fire.
Pressure should be equal
to the sum of outlet
pressure setting plus
pressure drop of the
valve.
a. Increase
inlet pressure
if possible.
Incorrect outlet
pressure adjustment of
pressure regulator.
Read manifold pressure
using manometer and
compare with the
pressure stated on the
specification plate.
a. See valve
adjustments
on page 37.
8. Erratic or pulsating
flame.
Wiring is run next to
high voltage switching
circuits causing induced
voltages.
Temporarily wire each
selector/sensor and
MR212 externally and
observe heater/
equipment operation.
a. If smooth
operation
results, isolate
effected wiring
from source of
induced
voltage.
Faulty amplifier or
erratic voltage supply.
With test resistor
connected and selector
dial locally connected,
turn selector dial through
entire modulating range.
Observe DC voltage
across modulator
terminals.
a. If erratic or
unstable DC
voltages are
obtained
throughout the
modulating
range, the
amplifier may
be assumed
faulty. Replace.
Table 17.
Trouble shooting guide for Modulating Discharge Temperature (MDT)
Controls (continued)
Symptom
Probable Cause
Field Test
Solution
