MUA-SVX01A-EN • Direct-Fired Make-up Air
85
Trouble Shooting
b. If erratic
operation is
noted only
over a small
range of 2 or
3-volts, the
voltage
sources may
contain surges.
Consult factory
for other
solutions.
9. Incorrect discharge
air temperature.
Inlet air sensor is used. Inlet air sensor changes
1° for each 3.5°, 5° and
8° outside temperature
change from 60°
(predetermined -
turndown varies with
model used).
a. Sensed
temperature
will vary from
remote
temperature
selector
settings. This
is intentional.
Incorrect wiring.
Check wiring diagram for
heater.
a. Correct
wiring.
System out of
calibration.
Sensed temperature
(thermometer next to
discharge air sensor does
not respond to remote
temperature selector
setting.
a. See
calibration
procedure.
Improper discharge air
sensor location.
Sensed temperature
(thermometer next to
discharge air sensor) does
not represent average
discharge air
temperature.
a. Move
discharge air
sensor to
location where
average
representative
temperature
can be sensed.
Room override
thermostat circuit
closed.
Remove override
thermostat lead form
terminal 2 of remote
temperature selector.
a. Check
remote
temperature
selector dial
setting, then
verify
thermostat
setting and/or
wiring for
shorts.
10. Burned out
transformer.
Short circuit in
modulator coil.
Measure resistance across
modulator terminals with
red lead wires
disconnected.
a. Replace
modulator
head if less
than 40 ohms.
Short circuit between
amplifier and modulator
valve.
Inspect wiring.
a. Correct
wiring if short
is found.
Table 17.
Trouble shooting guide for Modulating Discharge Temperature (MDT)
Controls (continued)
Symptom
Probable Cause
Field Test
Solution
