High Pressure Safety Switch - MCi MC8 Crusader Maintenance Manual

MAINTENANCE
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MC-8
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MANUAL
3) Open valve slowly and note pressure when light
goes on. (34-36 psi.)
ADJUSTMENT
Turn adjusting screw "A" (Fig. 16-48) to obtain
low pressure cut-out of 2 7 psi.
Turn adjusting screw "B" to obtain a low pressure
cut-in of 35 psi.
For refrigerant 500 the capacity control switch cut
out should be set at 33-35 psi. The cut-in setting
should be 42-44 psi.
HIGH PRESSURE SAFETY SWITCH
A high pressure safety switch is connected to the
high pressure side of the refrigerant system at the
receiver tank.
This switch provides protection from excessive
refrigerant pressure. When a malfunction occurs
within the compressor unloading system the switch is
activated and turns on the condenser blower when
refrigerant pressure is in excess of 275 psi. regardless
whether the A/C master switch is "ON" or "OFF".
B A
Figure 16-49: High Pressure Safety Swf tch
/v\ounted in the Condenser
Compartment.
Such action removes heat from the condenser coil
and reduces refrigerant pressure. The operation is
automatic, and will operate regardless of the heating
and air conditioning switch position.
In the normal position, the switch contacts enable
the operator to control the condenser blower motor
by the A/C & Heating switch.
In a high pressure condition, the safety switch con-
tacts feed power directly from the battery buss bar to
the condenser motor magnetic switch and the A/C
warning light.
In turn, the magnetic switch feeds power directly
from the buss bar to the condenser blower motor. As
pressure falls to approximately 250 psi. the switch
returns to normal operation.
TESTING HIGH PRESSURE SAFETY SWITCH
To test for proper operation under high pressure:
I) Turn A/C & Heating switch to "OFF" position.
2) Lift off Circuit No. 57 from Stud No. 57 at front
junction panel (IO Ga. Yellow-Gree_n).
Temporarily tape end of this wire.
3) Jumper a hot buss bar and Stud No. 9 in the rear
junction box to feed power directly to the com-
pressor unloading solenoid. Jumper buss bar to
Stud 36 to energize the scavenge solenoid.
4) Install a 0-300 (min.) gauge at the compressor
discharge service valve.
5) Run engine at fast idle and watch the discharge
line pressure. If condenser motor does not cut-in
at 275 psi., shut off the system IMMEDIATELY
and recheck wiring. The condenser motor should
then cut-out when refrigerant pressure drops to
250 psi.
ADJUSTMENT
Turn adjusting screw "B" (Fig. 16-49) to obtain a
cut-out pressure of 275 psi.
Turn adjusting screw "A" to obtain a cut-in
pressure of 250 psi.
For refrigerant 500 the High Pressure safety switch
cut in should be at excess of 335 psi.
PURGE COCK
The purge cock is located in the upper R.H. side
l .
Purge Cock