SECTION 22: HEATING AND AIR CONDITIONING
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version – Rev.1 Feb 2015)
39
7.12.2 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 or replace air
filter. Check return ducts for obstructions. Check
blower motor.
Frequent starting and stopping on low pressure
control switch.
Lack of refrigerant. Check for leaks. Recharge.
Compressor intermittently starts and stops.
Intermittent contact in electrical control circuit.
Compressor valves not in operating position.
Non-condensable in the refrigeration system.
Leak on system, system in vacuum in low temp.
Specific symptom, pressure in system will not
correspond to ambient temperature on shutdown.
Only non-condensable will cause this.
(Example: Pressure of idle R-134a system in
80°F (26.6°C) room should be 86.4 psi (595.7
kPa). See temperature chart in this section.)
