MCi MC8 Crusader - High Low Pressure Switch

Crusader
MC-8
[ "°' 16-34
HIGH LOW PRESSURE SWITCH
The. Hi-Lo pressure cut-out switch prevents the
operat10n of the system when refrigerant pressures
are above or below preset limits.
When pressures exceed the limits, the switch in-
terrupts the loading solenoid circuit and unloads
compressor. Low pressure cut-out and cut-in limits
are adjustable; high pressure cut-out limit is ad-
Justable, but the cut-in limit is fixed and non-
adjustable.
B A
C
Figure 16-47: Hi-Low Pressure Switch
Mounted in front of A/C
Compressor
TESTING HI-LO PRESSURE SWITCH
I) Connect test light to stud No. 4 on junction block
to check Hi-Lo pressure switch.
2) Install service gauges at the compressor suction
and discharge shut-off valves.
3) Operate the air conditioning allowing the system
to stabilize. (Approx. IO min.)
Low Pressure: Close suction valve slowly, noting
the pressure when the light goes out (4-6 psi.). Open
valve slowly and note when light goes on (35-38 psi.).
High Pressure: Open condenser door and cover
condenser core if necessary in order to raise the high
pressure. Note the pressure when the light goes out
(275 psi.). Close the condenser door and note
pressure when the light goes on (approx. 220) (psi.
not adjustable).
ADJUSTMENT
To make adjustments; remove control cover to per-
mit viewing direct reading scale plates. Gasketed
MAINTENANCE
DA rE ~Ju:.c_J__I y_L_, --'-19~73~-l MANUAL
screws m control case can be removed for
screwdriver adjustment or adjustment can be made
with a service wrench without removing gasketed
screws.
Set adjusting screw "A" (Fig. 16-47) at 5 lbs. for
the low pressure cut-out limit.
Set adjusting screw "B" at 38 lbs. for the low
pressure cut-in limit. (Tolerances ± 3 lbs.)
Set high pressure cut-out screw "C" at 275 lbs. The
high pressure cut-in differential is factory-set at ap-
proximately 55 lbs. below cut-out pressure.
For refrigerant 500 the hi-low pressure switch cut
out should be set at 325 psi. The cut-in setting should
be 55 psi. below 325 psi.
CAPACITY CONTROL SWITCH
A capacity control switch is mounted on one
bracket to the front of the A/C compressor mount
and is connected electrically in the "Loading Circuit''
and operates a loading solenoid which controls the
operation of one cylinder of the compressor. The
capacity control switch sense suction pressure and
unloads one cylinder when the suction pressure falls
to 27 psi. to reduce refrigeration capacity and driven
horsepower load during moderate to light air con-
ditioning requirements.
TESTING CAPACITY CONTROL SWITCH
I) To check capacity control switch connect test
light to terminal M-2 of that switch.
2) Close suction valve slowly noting pressure when
test light goes out. (26-28 psi.)
8 A
Figure 16-48: Capacity Control Switch
Mounted in front of A/C
Compressor