Fault Message:

CAB HUMIDITY SENSOR /WRG

Fault Code:

2163619ECS

Associated CAS:

HUMIDIFIER FAIL
(Advisory)

Air-Conditioning System Controller (ACSC) 2 does the Humidifier Control Unit (HCU) senses one of the conditions that follow:

• The humidity sensor (HHS) is out of range (5800 Hz)
• The temperature difference between the temperature sensor (HTS) and the ventilated temperature sensor (sensed by ACSC) is >10°C

ACSC 2 does not recognize the pin programming for the Humidifier option.

• Humidifier Control Unit (HCU) (A248)
• Humidifier Cabin Humidity Sensor (MT215)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Humidity Sensor MT215 actually contains Humidity Sensor (HHS) and Temperature Sensor (HTS).

1. Perform a wiring checks between HCU and HHS including the power and grounds.

   1. If wiring checks are not good, repair the defective associated wiring and do close out.
   2. If wiring checks are good, continue with next step.

2. Using a Scope, measure the Humidity signal coming out of the MT215 between MT215P1-5(+) and MT215P1-6(-). Signal should be a square wave with an amplitude of approximately 5 VDC with a frequency as per the table below:
   

   Number of pulse per second (Hz)	Humidity (%)
   < 5771	105
   5874	100
   6063	90
   6233	80
   6388	70
   6532	60
   6668	50
   6801	40
   6933	30
   7070	20
   7214	10
   7370
   > 7453	-5

3. Using a DC Voltmeter, measure the Temperature signal coming out of the MT215 between MT215P1-3(+) and MT215P1-4(-). Temperature Output (VDC) = 0,05T where T = Temperature in °C.
4. If one of the signals from previous steps 2 or 3 is missing, continue with next step.
5. Replace HHS.

   1. If the system check is good, do close out.
   2. If the fault remains, continue with next step.

6. Replace HCU.
7. Do close out.

NOTE: Perform Functional Test of the Humidifier System (TASK 21-71-00-720-801) to confirm the system integrity. This task is the approved Return to Service (RTS) Test for the Humidifier System.

If the operator which to operate the humidifier on the ground as it operates in flight, then use the following attached procedure. Please note that the attached procedure is not approved for RTS and can only be used for troubleshooting purpose. Please note that the 3.5 hours delay can not be bypassed in this procedure.

Humidifier Operation with Aircraft W off W (3.5 hours delay activation).