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Revision:
WA900-3EO
FAULT ANALYSIS CHART NOTES
7. THERMAL EXPANSION VALVE TOO
SMALL
If the replacement thermal expansion valve is
too small, it cannot pass a sufficient amount
of liquid to satisfy the evaporator.
Under conditions of heavy load, the super-
heat will be excessive and the system will
lose capacity.
Under conditions of light load, the system
may function properly. Too small expansion
valves usually result in abnormally low suc-
tion pressure.
8. THERMAL EXPANSION VALVE IS OB-
STRUCTED
Unless the expansion valve is properly pro-
tected by a strainer or filter, foreign matter
may obstruct the valve port.
If the obstruction is small, the resulting op-
eration will be much the same as though the
valve were undersized as described in 7
above.
If the obstruction holds the valve open during
shutdown, the operation will be as described
in 2 and 3. An obstructed expansion valve is
usually indicated by a partly warm evaporator.
9. SHORTAGE OF REFRIGERANT
A shortage of refrigerant will be initially indi-
cated by bubbles in the sight glass.
Frequently there will be a hissing or whistle at
the expansion valve.
The coil and suction line will be relatively
warm while the suction pressure will be low
due to little or no liquid being supplied to the
evaporator if the shortage is severe.
10. OVERCHARGE OF REFRIGERANT
An overcharge of refrigerant will cause high
head pressure.
Liquid will back up in the condenser and
decrease the amount of surface available for
condensing and as a result the head pressure
will rise.
In extreme cases, it may rise to a point where
high pressure cut-out will stop the compres-
sor. This may result in “short cycling”, (com-
pressor cycles too frequently).
11. AIR IN SYSTEM
If air or other non-condensible gases are
present in the system, they will tend to move
toward and collect at the condenser.
The head pressure will rise to a point above
the pressure corresponding to the tempera-
ture at which the vapour is condensing.
In extreme cases, the pressure may rise to a
point where the high pressure cut-out may
stop the compressor.
12. BROKEN VALVES IN COMPRESSOR
Broken or leaky discharge valves in a com-
pressor are generally indicated by the suction
pressure rising rapidly as soon as the ma-
chine is stopped.
If the suction pressure rises faster than 13
kPa per minute, it is an indication that the
compressor discharge valves are not holding.
Before the compressor is opened, however, it
should be determined that the pressure rise
is not due to other causes such as a leaky
expansion valve.
FAULT DIAGNOSIS
