Instructions
8 | © Danfoss | DCS (CC) | 2018.07
FRCC.PI.059.A1.02
• Check that all safety devices are operational
and properly set (safety pressure switch set
point, mechanical relief valve if necessary, etc.).
Make sure that these devices comply with both
generally - and locally - applicable regulations
and standards (e.g. EN 378-2:2016).
• When using high-pressure switches or relief
valves, the setting must not exceed maximum
service pressure of any system component. Re-
fer to the Application Guidelines for relevant
condensing unit pressure safety limits.
• A low-pressure switch is recommended to
prevent operation under vacuum. Use a mini-
mum setting of 1.2 bar (absolute).
• Verify that all electrical connections are proper-
ly fastened and in compliance with local safety
regulations.
• A compressor crankcase heater is factory ins-
talled, ensure that it has been energized for a
minimum of 12 hours before initial start-up and/
or during prolonged shutdown periods.
10 - Start up
Never start the compressor in the absence of
a refrigerant charge.
• Do not bypass the LP or any other safety swit-
ches during start-up
• Check current draw and voltage levels.
• Monitor the oil sight glass to ensure proper oil
return to the compressor.After 2 to 4 hours of
operations under established conditions, check
the oil level and add oil if necessary (refer to TI
bulletin 3-025).
If oil return continues to perform poorly, further
investigation of the piping design is required.
• In all cases, the application limits of the compressor
must be respected; moreover, high superheat values
lead to high discharge temperatures and decrease
compressor capacity. The maximum discharge tem-
perature is 130°C: operating at a higher temperature
may result in refrigerant decomposition.
• Under steady-state operating conditions, check
refrigerant piping or capillary tubes for abnor-
mal vibrations (refrigeration line movement in
excess of 1.5 mm necessitates corrective actions,
pipe brackets, etc.).
• Ensure that refrigerant flow through the liquid
line sight glass (when mounted) is adequate and
that operating temperatures correspond with
system specifications.
• When needed, refrigerant may be added in the
liquid phase, carefully throttling the refrigerant
on the low-pressure side and as far as possible
from the compressor.The compressor must be
operating during this process.
Do not overcharge the system.
11 - Troubleshooting
•
Compressor failure to start:
verify that the
compressor is hooked up to the power supply;
check the power lead connections and all sui-
table capacitors on single-phase models. If these
verifications reveal no abnormality, control the
motor windings with an ohmmeter.
Note: when the internal motor protector has
tripped out, it may take up to several hours to
reset and restart the compressor.
• Compressor failure to build up pressure:
check to make sure that all bypass valves in the
system have not been opened. Also check that
all solenoid valves are in their proper position.
If the internal pressure relief valve is open, the
compressor sump will be warm and the com-
pressor will trip out on the motor protector. If
this happens, it may take up to 2 or 3 hours to
reset and automatically restart the compressor.
• Abnormal running noise on the system:
- Ensure the absence of any liquid flood-back
to the compressor by means of measuring the
return gas superheat and compressor sump
temperature. The sump should be at least 10K
above the saturated suction temperature under
steady-state operating conditions.
- Check that the fans are running free and wit-
hout vibration.
• The high-pressure switch trips out:
check
condenser operations (condenser cleanliness,
fan operations, etc.). If above check out OK, the
problem may be due to either refrigerant over-
charging or the presence of a non-condensable
(e.g. air, moisture) in the circuit.
• The low-pressure switch trips out:
check eva-
porator operations (coil cleanliness, fan opera-
tions, water flow, water filter, etc.), liquid refrige-
rant flow and pressure drops (solenoid valve, filter
dryer, expansion valve, etc.), refrigerant charge.
• Low refrigerant charge:
the correct refrige-
rant charge is given by the liquid sight glass
indication, the condenser delta T in relation to
the refrigerant pressure tables (pressure-tempe-
rature), the superheat and the sub-cooling, etc.
(if additional charge is deemed necessary, refer
to the
«Filling the system»
section).
• Compressor maximum short cycling:
there
must be a minimum delay of five minutes
between two compressor starts. DCC recom-
mends the compressor should run at least two
minutes after each start, and between each stop
and start must be three minutes standstill. Only
during pump down cycle, the compressor may
run much shorter until the pumpdown pressure
has been reached or when safety devices will
prohibit compressor further operation.
12 - Maintenance
• Proper operations and maintenance of the
condensing units serve to prevent against sys-
tem-related problems.The following preventive
maintenance checks, to be performed at regular
intervals, are highly recommended:
- Control operating conditions (evaporating
temperature, condensing temperature, com-
pressor discharge temperature, temperature
difference on heat exchangers, superheat,
sub-cooling). These conditions must always re-
main within compressor operation limits.
- Verify that safety devices are operational and
properly set.
- Check the compressor oil level and quality;
this step may include an acid test, humidity
check, spectrometer analysis, etc. whenever the
oil becomes discolored.
- Ensure that the circuit is leak tight.
- Verify the proper operation of heat exchan-
gers and, if necessary, clean them.
- Check that the fans are running free (without
vibration) and current draw on the compressor
motor as well as proper voltage balance between
phases.
- Note 1: The condenser must be checked at
least once a year for clogging and be cleaned if
deemed necessary. Access to the internal side of
the condenser takes place through the fan pa-
nel.
Microchannel coils tend to accumulate dirt on
the surface rather than inside, which makes
them easier to clean than fin-&-tube coils.
- Change the filter dryer when necessary.
- Check that all electrical connections are still
adequately fastened.
- Make sure the condensing unit is clean and
in good working order; verify the absence of rust
or corrosion on components under pressure and
electrical connections.
- Make sure the refrigerant charge is suitable
for both winter and summer operation.
• Ensure that periodic in-service inspections re-
quired by local regulations are performed.
- Note 2: Remove surface dirt, leaves, fibers,
etc. with a vacuum cleaner, equipped with a
brush or other soft attachment. Alternatively,
blow compressed air through the coil from the
inside out, and brush with a soft bristle.
Do not use a wire brush. Do not impact or scrape
the coil with the vacuum tube or air nozzle.
13 - Replacement
Precaution must be taken when disconnec-
ting any components, cutting or drilling holes in
the tubing to ensure that no refrigerant under
pressure is present in the system.
The refrigerant shall not be discharged direc-
tly into the atmosphere; rather, it must be remo-
ved using approved reclamation techniques and
equipment and then safely stored, inaccordance
with applicable legislation.
The presence of refrigerant vapor can displace
air and lead to suffocation. Proper ventilation is
mandatory at all times when servicing the equip-
ment.
A condensing unit component change must be
carried out in compliance with local regulations.
• Make sure that the main power supply has
been switched off.
• Before replacement, it is necessary to deter-
mine the cause of failure and implement reme-
dial action. If such analysis and repair are not
performed, repetitive failure may occur. Note
that an oil acidity test always proves helpful in-
diagnosis when undertaking compressor repla-
cement.
• Check that the replacement component has
the same electrical and refrigeration perfor-
mance characteristics as the original one.
