Komatsu 830E, Shop Manual

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M09010 05/02 Air Conditioning System M9-7
for HFC 134a Refrigerant
TRINARY™ SWITCH
This switch is mounted on the receiver-drier and has
three functions, as implied by the name:
1. Disengage the compressor clutch when sys-
tem pressure is too high.
2. Disengage the compressor clutch when sys-
tem pressure is too low.
3. Engage and disengage the radiator fan drive
clutch during normal variation of system pres-
sure.
The Trinary™ switch performs three distinct functions
to monitor and control refrigerant pressure in the sys-
tem. This switch is installed on the receiver-drier. The
switch functions are:
Terminals 1 & 2 are connected internally through two,
normally closed pressure switches in series, the low
pressure switch and the high pressure switch.
Terminals 3 & 4 are connected internally through a nor-
mally open switch that is used to control the clutch that
drives the radiator fan. This switch closes and causes
the cooling fan clutch to engage when system pressure
rises to 200 - 230 psi. When pressure falls to 140 - 195
psi, the switch contacts open, and the cooling fan
clutch disengages
•
Low Pressure - This switch opens and disen-
gages the compressor clutch if system pres-
sure drops into the 15 -30 psi range. When
pressure rises above 40 psi, the switch contacts
close, and the clutch engages the compressor.
Since temperature has a direct effect on pres-
sure, if the ambient temperature is too cold,
system pressure will drop below the low range,
and the pressure switch will disengage the
clutch.
•
Fan Clutch - The mid-range function actuates the
engine fan clutch, if installed.
•
High Pressure - This switch opens and disen-
gages the compressor clutch if system pressure
rises above the 300 - 350 psi range. After sys-
tem pressure drops to 210 - 250 psi, the switch
contacts will close and the clutch will engage.
The switch functions will automatically reset when sys-
tem pressure returns to normal.
The pressures listed above are typical of pressures
at the receiver-drier. Due to normal system flow
losses and the distance between the service port
and the receiver-drier, it is expected that actual
system pressure displayed on the gauge will nor-
mally be approximately 20 psi higher. This factor
should be observed when checking for proper
operation of the switch.
NOTE: One other pressure controlling device is
installed within the compressor. A mechanical relief
valve is located on the back of the compressor. The
relief valve will open at 500 - 550 psi. The purpose of
this valve is to protect the compressor in the event that
pressure should be allowed to rise to that level. Dam-
age to the compressor will occur if pressure exceeds
550 psi.
OPENS CLOSES
Low
Pressure
15-30 psi -
descending
pressure
40 psi -
rising pressure
High
Pressure
300-350 psi 210-250 psi
Fan Clutch 35-60 psi -
below closing
pressure
200-230 psi -
rising pressure