40 Chapter 6 System Maintenance
New Liebert_DM Series Air Conditioner User Manual
6.2.8 High-Pressure Switch And Low-Pressure Switch
The discharge pressure and suction pressure will vary greatly with the AC unit load and ambient conditions (refer to
Table 6-1) during normal operation. When the discharge pressure rises to the high-pressure setpoint, the
high-pressure switch will activate and the control system will shut down the compressor after ensuring an abnormal
input signal of the high-pressure switch.
When the suction pressure is lower than the low-pressure setpoint, the low-pressure switch will activate and the
control system will shut down the cooling system after confirming.
Table 6-1 Typical discharge pressure and suction pressure
6.2.9 Compressor
The compressor fault is generally classified into two types:
1. Motor fault (such as winding burnout, insulation failure, short-circuit between coils and so on).
2. Mechanical fault (such as compressing failure, relief valve fault, therm-o-disc fault and so on).
If the operation pressure is not established, it indicates that the compressor has failed. It can be confirmed if the
suction pressure and discharge pressure are balanced and the motor does not rotate reversely.
The controller has powerful alarm and protection functions to ensure safe operation of the compressor. The
maintenance personnel should record the high pressure and low pressure and find out the cause of an alarm
protection during periodical maintenance and inspection.
Note
Avoid touching or contacting the residual gas and oils in compressor with exposed skin. Wear long rubber gloves to handle
contaminated parts.
Check the following items before replacing the compressor:
1. Check that all fuses and circuit breakers are normal.
2. Check the working status of the high and low pressure switches.
3. Check the relevant historical alarm information.
4. Check the historical operation records of the compressor.
5. Check the motor electric characteristic.
Note
System contains refrigerant. Reclaim the refrigerant using standard reclaiming equipment before maintenance.
Follow the following procedures to remove and replace the failed compressor:
1. Cut off the power.
2. Attach suction and discharge gauges to compressor access fittings.
3. Reclaim the residual refrigerant by using standard reclaiming procedures.
Note
Release of refrigerant to the atmosphere is harmful to the environment. Refrigerant must be recycled in accordance with state and
local regulations.
4. Remove the failed compressor.
5. Follow manufacturer’s instructions to clean out kits.
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