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SYMPTOM
Control signal is not at full range.
There is no control signal.
The controller is out of calibration.
Humidity sensor is not installed properly.
Humidity exceeds set
point
Actuator is not working.
There is high steam pressure.
Boiler is not operating correctly.
Control signal is not at full range.
Control polarity has been reversed.
Controller is out of calibration.
Humidity sensor is not installed properly.
Actuator is not working.
Humidity remains below
set point
There is high steam pressure.
Boiler is not operating correctly.
There is an airflow switch fault.
The high limit controller is not in
the correct location.
The humidifier is too small.
The humidifier is too large.
There is a high limit controller fault.
Evaporation distance is too short.
Condensate in unit
Steam valve is leaking.
The trap height is incorrect.
Valve sizing is incorrect.
Steam leaks from P-traps
There is excessively high steam pressure.
LEGEND
AHU — Air-Handling Unit
Table 50 — Humidifier Troubleshooting (cont)
POSSIBLE CAUSES
POSSIBLE REMEDIES
Verify and, if necessary, correct compatibility of the full range control sig-
nal to the valve actuator.
Verify and, if necessary, correct control signal polarity to the valve
actuator.
Check and, if necessary, correct calibration of controller.
Ensure that humidity sensors are installed correctly and not located in
drafts (wall). If necessary, correct sensor installation.
Remove actuator and test to verify that it is operational. If not, clean or
replace jammed valve.
Verify that the steam pressure has not changed. Excessively high pres-
sure could jam the valve.
Verify stable boiler pressure. Wide swings in pressure could affect the
humidity controls.
Verify and, if necessary, correct compatibility of the full range control sig-
nal to the valve actuator.
Verify and, if necessary, correct control signal polarity to the valve
actuator.
Check and, if necessary, correct calibration of controller.
Ensure that humidity sensors are installed correctly and not located in
drafts (wall). If necessary, correct sensor installation.
Remove actuator and test to verify that it is operational. If not, clean or
replace jammed valve.
Verify that the steam pressure has not changed. Excessively high pres-
sure could jam the valve.
Verify stable boiler pressure. Wide swings in pressure could affect the
humidity controls.
Ensure that airflow switch is not fluttering. If necessary, correct
fluttering airflow switch.
Verify that high-limit controller is not located too close to steam
discharge manifolds. If necessary, correct location of controller.
Humidifier is undersized. Check humidity load calculations.
Verify humidifier capacity versus air volume.
Verify that high limit controller is working. If necessary, correct problem.
Verify and, if necessary, correct evaporation distance to obstructions or
elbows.
Verify steam valve is not leaking. If necessary, correct leaking steam
valve.
Ensure that height of trap exceeds the static pressure of the duct/AHU,
especially if under negative pressure.
Check valve sizing to maximum manifold capacity. If necessary, resize
valve within manifold capacity.
Check that inlet steam pressure does not exceed humidifier capability.
268
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