These caution messages show if hydraulic system pressure is below 1200 psi:
*
HYD PRESS SYS L

*
HYD PRESS SYS C

*
HYD PRESS SYS R

*
HYD PRESS SYS L+C

*
HYD PRESS SYS R+C

*
HYD PRESS SYS L+R

*
HYD PRESS SYS L+C+R.

Hydraulic Pump Pressure Indications
The maintenance page shows hydraulic pump pressure in psi.
Advisory messages show if hydraulic pump pressure is less than 1200 psi for ACMPs or 1800 psi for ADPs and EDPs. These are the advisory messages:
*
HYD PRESS PRI L

*
HYD PRESS PRI C1

*
HYD PRESS PRI C2

*
HYD PRESS PRI R

*
HYD PRESS DEM L

*
HYD PRESS DEM C1

*
HYD PRESS DEM C2

*
HYD PRESS DEM R.

These advisory messages do not show for a demand pump when the demand pump selector is in AUTO and there is no control signal from HYDIM to operate the pump.
29-30-00

Page 11 D633W101-BEJ Sep 05/2003

HYDRAULIC INDICATING SYSTEM -PRESSURE INDICATING

Also, these advisory messages do not show if the system pressure is low.
Status messages show if there is a signal for a pump to operate and the pump pressure is less than 1200 psi for ACMPs or 1800 psi for ADPs and EDPs. These are the status messages:
*
HYD PUMP PRI L

*
HYD PUMP PRI C1

*
HYD PUMP PRI C2

*
HYD PUMP PRI R

*
HYD PUMP DEM L

*
HYD PUMP DEM C1

*
HYD PUMP DEM C2

*
HYD PUMP DEM R.

These status messages also show if there is a pump overheat condition.
The status and advisory low pressure messages for the EDPs do not show if the related engine speed for the EDP is less than idle.
Low pump pressure also makes the pump fault light on the hydraulic control panel come on. The pump fault light does not come on for a demand pump when the demand pump selector is in AUTO and there is no control signal from HYDIM to operate the pump.
Reservoir Pressure Indications
Hydraulic reservoir pressure (LO or NORM) shows on the hydraulic maintenance page. LO shows when the pressure is 21 psia or less. NORM shows when the pressure is 25 psia or more.
These status messages show if the hydraulic reservoir pressure is low:
*
HYD RSVR PRESS L

*
HYD RSVR PRESS C

*
HYD RSVR PRESS R.

EFFECTIVITY BEJ ALL  29-30-00 
Page 12 
D633W101-BEJ  Sep 05/2003 

HYDRAULIC INDICATING SYSTEM -PRESSURE INDICATING

EFFECTIVITY BEJ ALL  29-30-00 
Page 13 
D633W101-BEJ  May 05/2003 

777 AIRCRAFT MAINTENANCE MANUAL

THIS PAGE IS INTENTIONALLY LEFT BLANK

29-30-00

Page 14 D633W101-BEJ May 05/2003

HYDRAULIC INDICATING SYSTEM -TEMPERATURE INDICATING

General

Temperature transducers for each hydraulic reservoir and each hydraulic pump send analog temperature signals to the HYDIM cards. The HYDIM cards convert the analog signals to digital values and detect overheat conditions. The temperature and fault data are sent over the ARINC 429/629 bus to the EICAS, the AIMS, and the CMCS for flight deck display and maintenance support.
Each ACMP has a temperature switch that is a part of the pump.
BEJ ALL PRE SB 777-29-0024
The ACMP temperature switch is not used.
BEJ ALL POST SB 777-29-0024

The ACMP temperature switch provides an overheat signal that is independent of the temperature transducer.
NOTE: The ACMP temperature transducer is located in the ACMP pressure/case drain filter module, approximately 15 inches from the ACMP. Some ACMP failure modes can stop the flow of hydraulic fluid from the case drain and cause a pump overheat condition that is not detected by the case drain temperature transducer.
BEJ ALL
EFFECTIVITY
BEJ ALL

Sensor Functional Description
The temperature transducers are RTD (resistance temperature detector) type transducers. The transducer provides an electrical signal to the HYDIM card that varies from 4 to 20 milliamperes to indicate temperatures between -54C and 149C (-63.6F to 300F).
The HYDIM temperature value is fixed at -54C for an electrical signal that is less than or equal to 4 milliamperes.
BEJ ALL PRE SB 777-29-0024
The HYDIM temperature value is fixed at 149C for an electrical signal that is equal to or greater than 20 milliamperes.
An electrical signal of less than 1 milliampere or more than 23 millamperes indicates a temperature transducer fault.
BEJ ALL POST SB 777-29-0024
For the EDP and ADP, the HYDIM temperature value is fixed at 149C for an electrical signal that is equal to or greater than 20 milliamperes.
　
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