Cold Weather Maintenance - Air Conditioning

TASK 12-31-21-660-001-A
Cold Weather Maintenance - Air Conditioning

1. Reason for the Job
This procedure gives the cold weather maintenance practices for the air conditioning.
2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
TASK 12-31-31-660-001-A	Cold Weather Maintenance - Indicating/Recording systems and Navigation
TASK 12-31-38-660-001-A	Cold Weather Maintenance - Water/Waste
TASK 12-31-49-660-001-A	Cold Weather Maintenance - Auxiliary Power Unit
TASK 12-33-21-618-001-A	Pre-conditioning through the LP Ground Connection (Aircraft Electrical Power Available)
TASK 12-33-21-618-001-A-01	Pre-conditioning through the HP Ground Connection
TASK 12-33-21-618-001-A-02	Pre-conditioning with the APU

3. Job Set-up
Subtask 12-31-21-660-050-A

A. General
(1) To know if pre-conditioning is necessary, refer to tables 1 and 2 in the cold weather practices for the water/waste system (Ref. AMM TASK 12-31-38-660-001).

CAUTION: DO NOT ENERGIZE THE AIRCRAFT ELECTRICAL NETWORK IF:

THE TEMPERATURE IN THE AVIONICS COMPARTMENT IS EQUAL TO OR LESS THAN -40°C (-40.00°F), AND
THE CIRCUIT BREAKERS FOR THE COMPUTERS IN THE AVIONICS COMPARTMENT ARE CLOSED.

BEFORE YOU ENERGIZE THE ELECTRICAL CIRCUITS IN THESE TEMPERATURES, YOU MUST OPEN THE CIRCUIT BREAKERS. IF THE CIRCUIT BREAKERS STAY CLOSED, PERMANENT DAMAGE CAN OCCUR TO THE COMPUTERS.

(2) Avionics Bay Temperature

NOTE: The temperature factor for operation of those computers located in the aircraft avionics bay is the avionics bay temperature.
You must measure the temperature in the avionics bay with a suitable temperature measuring device.

(3) If the temperature in the aircraft avionics bay is between -40 deg.C (-40.00 deg.F) and -15 deg.C (5.00 deg.F):

do not energize the aircraft electrical circuits before the related computer systems circuit breakers are open.

4. Procedure
Subtask 12-31-21-660-051-A

A. Pre-conditioning Recommendations
(1) If the avionics bay temperature is equal to or less than -40 deg.C (-40.00 deg.F) you must do the pre-conditioning through the Low Pressure (LP) ground connector (Ref. AMM TASK 12-33-21-618-001).
(2) If the avionics bay temperature is between -15 deg.C (5.00 deg.F) and -40 deg.C (-40.00 deg.F) you must do the pre-conditioning through:

the LP ground connector (Ref. AMM TASK 12-33-21-618-001) or,
the High Pressure (HP) ground connector (Ref. AMM TASK 12-33-21-618-001).

NOTE: When you do the pre-conditioning through the HP ground connector:

it is possible to operate the avionics bay computers in this temperature range but incorrect operation of the computers can occur (Ref. AMM TASK 12-31-31-660-001).
this may cause the pre-conditioning to stop.
this can be because of the temperature conditions and not necessarily through a technical malfunction.

(3) If the avionics bay temperature is above -15 deg.C (5.00 deg.F)you must do the pre-conditioning:
(a) Through the LP ground connector (Ref. AMM TASK 12-33-21-618-001),
(b) Through the HP ground connector (Ref. AMM TASK 12-33-21-618-001) or
(c) With the APU (Ref. AMM TASK 12-33-21-618-001) and (Ref. AMM TASK 12-31-49-660-001).

[Rev.10 from 2021] 2026.04.01 04:22:10 UTC