*
The override valve goes to the OVRD position

*
Forward cargo heat valve closes (except low flow does not effect the valve position)

*
The bulk cargo ventilation fan goes off (only if the equipment cooling switch is in the OVRD position)

*
Vent valve usually goes to the opposite position of the forward cargo heat valve. Vent valve closes if the forward cargo fire system is armed.

The LOW FLOW -OVRD MODE signal applies only to the supply fans, vent fan, and the override valve. The signal does not effect the operation of the forward cargo heat valve or the vent valve.
Flight deck effects that relate to the override mode are controlled by the position of the override valve. When the valve is in the override position, these flight deck effects show:
*
OVRD light in the override switch

*
EQPT COOLING OVRD advisory message.

If the override valve does not go the override position, the flight deck effects for the override mode do not show. See the functional description of the override valve in this section for more information about the override valve.
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A/C -EQUIPMENT COOLING -FUNCTIONAL DESCRIPTION -OVERRIDE MODE

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A/C -EQUIPMENT COOLING -FUNCTIONAL DESCRIPTION -CONTROLLER

General
Control logic for the right equipment cooling controller (ECC) is shown; the left is similar.
The right ECC gives control for the supply fans and the override valve. The ECC normally controls the fans and valve with inputs from the right or left ECSMC. The ECC does not use the inputs from the ECSMC if takeover control logic (see below) is true.
Inputs
The right ECC gets control power from the P210 right power management power. The controller gets inputs from these components for takeover control logic and to control the fans and the valve:
*
Right ECSMC

*
Left ECC, L ECSMC and MEC low flow sensor through the ECC cross talk

*
PSEU 2

*
Flight deck low flow sensor.

The controller uses the inputs to calculate if it should control the fans and override valve. It can use ECSMC inputs for normal control, or it can takeover control and use ECC fan/valve control logic.
EFFECTIVITY BEJ ALL
Takeover Control Logic
The ECC takes control away from the ECSMCs when the airplane is in the air and any one of the following sets of conditions occur:
*
Both ECSMCs try to control the fans and valve at the same time and both ECCs operate normally

*
Left ECC is failed or there is low flow in the MEC supply duct and in the flight deck supply duct and the override valve is in the NORM position for more than 6.5 minutes

*
Left ECC is failed or there is low flow in the MEC supply duct and in the flight deck supply duct and the override valve is in the OVRD position for more than 20 minutes.

Once the controller takes control it will not return control to the ECSMCs until the airplane is on the ground.
ECC Fan/Valve Control Logic
The controller uses the ECC fan/valve control logic to make the low flow condition go away. The controller uses a combination of supply fans on/off and override valve positions to do this. There are six combinations (modes). The controller tries each mode for 60 seconds. After 60 seconds the controller will try the next mode. If the low flow goes away the controller stays in that mode. If the low flow condition returns, the controller will select the next mode. After all modes have been tried, the controller starts over with mode 1. These are the six sets of modes:
* Left supply fan off, right supply fan off, and left override valve motor selected to the OVRD position
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A/C -EQUIPMENT COOLING -FUNCTIONAL DESCRIPTION -CONTROLLER

*
Left supply fan off, right supply fan off, and right override valve motor selected to the OVRD position

*
Left supply fan on, right supply fan off, and left override valve motor selected to the NORM position

*
Left supply fan on, right supply fan off, and right override valve motor selected to the NORM position

*
Left supply fan off, right supply fan on, and left override valve motor selected to the NORM position

*
Left supply fan off, right supply fan on, and right override valve motor selected to the NORM position.

Outputs
The ECC controls the supply fans and the override valve through separate control channels. The right ECC sends output control signals to these items:
　
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