Carrier DB-S Series Use & Maintenance Instructions page 19

4. Inadequate performance of the unit:
If the unit's performance is not adequate, and no technical causes or anomalies can
be identified, it is necessary to check that the cell doors are perfectly sealed, that
there are no leaks from the cell, that no foodstuffs or non frozen liquids have been
inserted in the low temperature cell and that no ice has formed on the evaporator.
It is therefore advisable to locate the unit away from doors, especially if these are
opened several times a day.
WARNING:
It absolutely forbidden to remove the safety devices provided by the anufacturer
to protect operators while the machine is in operation.
5. Other malfunctions may be due to the triggering of the following electrical
safety devices:
a) Fan thermal protection (incorporated in the motor) - automatic resetting. This
device is designed to safeguard electrical fans against excessive current absorp-
tion due to:
- overheating
- lack of one phase (only for three phase models)
- dirt in the condenser
- ice in the evaporator
b) Discharge Line Thermostat
Protects the compressor against elevated discharge temperatures which can
typically occur in certain conditions such as low gas charge or failed condenser
fan.
c) High pressure switch - manual resetting
It is designed to protect the compressor from excessive pressure, which cause
the pressure switch to be triggered too often, deriving from:
- dirt in the condenser
- condenser fans not working
- excessive temperature in the room where the system is located
- use of the system in unsuitable conditions or with inappropriate products.
To reset press the button on the pressure switch.
d) Low pressure switch - automatic resetting
It is generally used to stop the unit working in pump-down mode.
The triggering of the pressure switch can also indicate excessively low pressure
in relation to the set points, due to one of the following causes:
- lack of gas due to the breakage of a pipe or to loose hub
- clogged up filters
- solenoid valve failure
- ice in the evaporator
The minimum and maximum temperature pressure switches and the oil pressure
switch are located inside the motor casing. Before resetting, disconnect from mains.
e) Thermistors - automatic resetting
These are inserted in the compressor's coil to protect the motor from overheating
(see electrical diagram)
f) Minimum and maximum tension electronic relay (Monitor) - automatic reset
(where applicable). It is used to protect the unit against anomalies in the power
supply (+/-12% of nominal value). The unit starts with a delay of 8 minutes, indi-
cated on the panel by a LED.
The main factors that cause the triggering of the device are anomalies in the
power supply (for further information see attachment)
g) Phase sequencing relay
Is an electronic device which prevents the compressor from starting if the phases
are not connected in the correct sequence. This device can be found either in the
electrical panel or integtrated in the compressor protection module.
h) Condenser fans variable speed drive
Electronic system for checking the speed of condenser fans.
In case of system malfunction:
- turn off at mains
- open the electric control panel
- the variable speed drive is located inside the control panel.
Move the switch to position (1)
- close the electric control panel and reset the unit
- replace the variable speed drive as soon as possible
- having replaced it, move the variable speed drive to the automatic
position (0).
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