PREVOST X3-45 Multiplex, Maintenance Manual

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Section 22: HEATING AND AIR CONDITIONING
PA1562
31
PROBABLE CAUSE PROBABLE REMEDY
HIGH DISCHARGE PRESSURE
Air or non-condensable gases in condenser. Purge and recharge system.
Overcharge or refrigerant. Bleed to proper charge.
Condenser dirty. Clean condenser.
7.10.2 A/C
TROUBLE CAUSE
Low suction pressure and frosting at dryer outlet. Clogged filter.
Low Oil Level. Check for oil leaks and for leaking oil seal. Do not
attempt to check oil level unless system has been
stabilized at least 20 minutes. See oil level
verification.
Excessively cold suction line. Loss of contact between the expansion valve
bulb and the suction line or sticking of the
expansion valve.
Check for foreign matter and clean, repair or
replace the valve.
Excessively cold suction line and noisy
compressor. Check superheat adjustment. Check remote bulb
contact. Check expansion valve for sticking.
Compressor squeaks or squeals when running. Check oil level. Replace oil seal.
Noisy or knocking compressor. Check for broken internal parts. Overhaul if
required.
Compressor vibrates. Check and tighten compressor mounting bolts
and belt tension.
Low refrigerant level Check for refrigerant leaks and add refrigerant if
required.
Suction pressure rises faster than 5 pounds per
minute after shutdown. Check compressor valve for breakage or
damage.
Insufficient cooling. Check for refrigerant leaks. Check condition of air
filter and motors.
Insufficient air flow. Dirty or iced evaporator. Dirty air filter. Blowers
inactive. Clogged ducts.
No flow of refrigerant through expansion valve. Filter dryer is clogged. Remote bulb has lost
charge or expansion valve is defective.
Expansion valve hisses. Bubbles in moisture and
liquid indicator. Gas in liquid line. Add refrigerant.
Loss of capacity Clogged filter. Obstructed or defective expansion
valve.
Superheat too high. Reset superheat adjustment. Check for clogged
external equalizer line, or filter dryer.
Reduced air flow:
a. Dirty or clogged air filter;
b. Evaporator motor inoperative; or
c. Plugged return air ducts. Dirty or iced evaporator coil. Clean air filter
screen. Check return ducts for obstructions.
Check blower motor.
Frequent starting and stopping on low pressure
control switch. Lack of refrigerant. Check for leaks. Recharge.