MCi Crusader II 1989 Maintenance Manual page 490

Date
1-1-89
Page· __
1_6-_2_0 _ _
MC-9 MAINTENANCE MANUAL
EXPANSION VALVE TROUBLESHOOTING. (CONT'D)
Suction line too small.
LOW SUCTION PRESSURE, LOW SUPERHEAT
Wrong compressor pulley size.
Uneven or inadequate evaporator loading due to
poor air distribution or liquid flow.
HIGH SUCTION PRESSURE, HIGH SUPERHEAT
Compressor discharge valve leaking.
HIGH SUCTION PRESSURE, LOW SUPERHEAT
Valve superheat setting too low.
Compressor discharge valves leaking.
FLUCTUATING SUCTION PRESSURE
Incorrect superheat adjustment
FLUCTUATING DISCHARGE PRESSURE
Insufficient charge.
HIGH DISCHARGE PRESSURE
Air or non-condensable gases in condenser.
Overcharge of refrigerant.
Condenser dirty.
Insufficient cooling air distribution over air
cooled condenser.
LEAK TESTING LINES AND FITTINGS
All lines are copper tubing or Aeroquip No. 1540 hose.
The copper lines have soldered joints and the large hose
connections have a rubber O-ring seal.
LEAK TESTING - The most common method used is a
halide torch consisting of an acetylene tank, a burner and a
suction test hose.
WARNING: Do not inhale fumes from leak
detector.
The flow of acetylene to the burner causes a suction in
the test line. Any refrigerant gas present will be drawn
through the hose and into the burner where it decomposes
into free acids.
These acids come in contact
with
the hot copper reaction
plate in the burner, causing color reaction in the flame. A
small concentration is indicated by a green tint and a large
concentration by an intense blue.
Do not confuse this change in color
with
the ·change
caused by shutting off the air supply through the hose by
holding the end too close to an object.
Install proper size suction line.
Install proper size pulley.
Balance evaporator load distribution by providing correct air or
liquid distribution.
Replace or repair valve.
Adjust superheat as outlined under Superheat Adjustment.
Replace or repair discharge valve.
Adjust superheat to 8-12°F (4-6°C).
Add charge to system.
Purge and recharge system.
Bleed to-proper charge:
Clean condenser.
Properly_ locate condenser to freely dispel hot discharge air.
The procedure for testing is:
1. Adjust flame so the top of the cone is approximately
level or within
½
inch (12.7 mm) above the plate.
2. Probe end of suction test tube around all joints, valves,
etc. When a leak has been found at a soldered joint, that
section of the system must be pumped
down.
Do not solder
if pressure exists in the joint as pressure will force melted
solder away from joint.
If the system is empty, it is more economical to put in just
enough Freon to produce about 15 psi (103 kPa). The pres-
sure can then be raised to about 150 psi (1,035 kPa) with dry
nitrogen.
NOTE: This gas is put Into the suction and
discharge shut-off valves at the compres-
sor. The receiver valves must also be
opened.
If
no leaks are found, dump this
mixture, evacuate the system and charge
with refrigerant.