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05TA Service Manual

SERVICE OPERATIONS

7/24/13

9-13

Sentronic Sensor

(2D, 3D, 4D & 6D compressors before March 2011). The same oil pressure

sensor  is  used  for  all  Sentronics.    It  mounts  directly  into  the  oil  pump.    The  Sentronic  sensor
measures oil pump differential pressure.  It has an internal contact that opens on low oil pressure
and signals the Sentronic electronic control module to begin time out.  The same contact closes
when  proper  oil  pressure  is  present  and  stops  the  module  time  out.    Should  oil  pressure  fall
below 7-9 PSID for a period of two minutes, the Sentronic module will open the control circuit,
using its Normally-Closed (N) contact, and shut the compressor off.

Approximate oil pressure can be measured in the field.  Oil pumps are furnished with a Schrader
valve  mounted  on  the  oil  pump  discharge  port.    To  measure  oil  pressure,  subtract  crankcase
pressure from discharge oil pressure.  Tripping of the oil pressure safety switch is a warning that
the  system  has  been  without  proper  lubrication  for  too  long  a  time.    Repeated  trips  of  the  oil
pressure  safety  control  are  a  clear  indication  that  something  in  the  system  requires  immediate
remedial action.

Sentronic Module

(2D, 3D, 4D & 6D compressors before March 2011). The Sentronic has in

addition to the (N) contact, used for compressor shutdown, a Normally Open (N.O.) contact that
can be used in an alarm circuit.  The Single Pole Double Throw (S.P.D.T.) contact of Sentronic
can  be  electrically  isolated  from  the  control  circuit  power  supply,  and  used  to  control  a  circuit
with a different voltage. Sentronic has a timing circuit that actually compares the amount of time
with good oil pressure to that with insufficient oil pressure and has a memory that will shut the
compressor down after a period of more than two minutes if the compressor has a "history" of oil
pressure fluctuations with more unacceptable than acceptable pressures.

Sentronic  also  has  a  memory  that  retains  the  compressor  oil  pressure  "history"  for  up  to  one
minute in the event of a power loss.  Sentronic uses a permanent magnet integral with the reset
button to reset its output control relay in the event of a trip.  When the reset button is depressed,
it magnetically pulls the Sentronic relay's armature to its original, reset position.  Sentronic needs
no voltage present to reset.

Coresense Protection

Discus compressors manufactured after March 2011 will be supplied with CoreSense Protection.
CoreSense replaces the Sentronic Oil Pressure Safety Module on all Discus compressors and the
Electronic Motor Protector Module on 4D & 6D compressors.  Note: 2D & 3D compressors will
continue to have Internal Line Break overload protection.

The oil pressure monitoring portion of the CoreSense will act very similar to the Sentronic Oil
Pressure Safety switch.  A current transformer (CT) in the compressor junction box determines
when  the  compressor  is  running  and  starts  monitoring  oil  pressure.    Note:    Wire  “T1”  passes
through CT before connecting to compressor terminal.