Maintenance Diagnostic; Refrigeration - Lennox FCM 85 Installation, Operating And Maintenance Manual

MAINTENANCE DIAGNOSTIC

REFRIGERATION

FAULT
LP PROBLEMS AND LP CUT
OUTS
FLEXYII_WSHP-IOM-1307-E
POSSIBLE CAUSE AND SYMPTOMS
Refrigerant charge too low
In Heat Pump Mode the temperature
difference between T outdoor and Tevap.
(Dew) is too high
5°C < Delta T < 10°C excellent
10°C < Delta T < 15°C acceptable
15°C < Delta T < 25°C too high
Refrigeration circuit blocked in distribution
Liquid line drier blocked. High temperature
difference between inlet and outlet of the
drier
Contaminant in the expansion valve
Expansion valve not adjusted properly
Ice plug in the expansion valve
Incorrect insulation of the thermostatic bulb
of the expansion valve
Low Pressure Switch cut out point too high
LP cut out due to not enough defrost on
heat pumps
SOLUTION
Measure the superheat and sub-cooling
Good if 5°C<SC<10°C and 5°C<SH<10°C
Bad if SC>10°C and SH too low
Check superheat adjustment and charge
unit (a leak check must be carried out)
If too high check the coils are clean or
check coil internal pressure drop between
the liquid line and the suction line
Good if < 3bar
Too high > 3 bar (coil blocked)
Stop the fan and create icing of the coil.
Check all circuits freeze evenly across the
whole surface of the coil
If some parts of the coil do not freeze this
could indicate a problem with the
distribution
Change filter drier
Attempt to free the valve adjusting element
by freezing the valve and then heating the
thermostatic element. Replace the valve if
necessary
Adjust the expansion valve
Heat the main body of the valve. If the LP
increases and then decreases gradually,
empty the circuit and replace the drier
Superheat too low: adjust superheat
Move the thermostatic element along the
pipe
Insulate the Thermostatic element of the
valve
Check the cut out pressure of the Low
Pressure switch: It must be 0.7+/- 0.2bar
and must closes at 2.24 +/- 0.2 bar
Adjust the CLIMATIC settings to extend the
defrost cycles or shorten the time between
defrosts
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