Mitsubishi Electric MXZ-8B140VA Technical & Service Manual page 22

8-2. CHECK POINTS FOR TEST RUN
8-2-1. Before test run
● Turn on the main power switch more than 12 hours before starting operation. Starting operation just after turning on the
power switch can severely damage the internal parts. Keep the main power switch turned on during the operation season.
● After completing installation and the wiring and piping of the indoor and outdoor units, check for refrigerant leakage, loose-
ness in the power supply or control wiring, wrong polarity, and no disconnection of one phase in the supply.
● Use a 500-volt M-ohm tester to check that the resistance between the power supply terminals and ground is at least 1 M".
● Do not carry out this test on the control wiring (low voltage circuit) terminals.
Warning: Do not use the air conditioner if the insulation resistance is less than 1 M".
Insulation resistance
After installation or after the power source to the unit has been cut for an extended period, the insulation resistance will drop
below 1 M" due to refrigerant accumulating in the compressor. This is not a malfunction. Perform the following procedures.
1. Remove the wires from the compressor and measure the insulation resistance of the compressor.
2. If the insulation resistance is below 1 M", the compressor is faulty or the resistance dropped due to the accumulation of
refrigerant in the compressor.
3. After connecting the wires to the compressor, the compressor will start to warm up after power is supplied. After supplying
power for the times indicated below, measure the insulation resistance again.
• The insulation resistance drops due to accumulation of refrigerant in the compressor. The resistance will rise above 1M"
after the compressor is warmed up for 4 hours. (The time necessary to warm up the compressor varies according to
atmospheric conditions and refrigerant accumulation.)
• To operate the compressor with refrigerant accumulated in the compressor, the compressor must be warmed up at least 12
hours to prevent breakdown.
4. If the insulation resistance rises above 1 M", the compressor is not faulty.
Caution:
• The compressor will not operate unless the power supply phase connection is correct.
• Turn on the power at least 12 hours before starting operation.
Staring operation immediately after turning on the main power switch can result in severe damage to internal parts.
Keep the power switch turned on during the operational season.
● The followings must be checked as well.
• The outdoor unit is not faulty. LED on the control board of the outdoor unit flashes when the outdoor unit is faulty.
• Both the gas and liquid stop valves are completely open.
8-2-2. Test run
(1) Using remote controller
Refer to the indoor unit installation manual.
• Be sure to perform the test run for each indoor unit. Make sure each indoor unit operates properly following the installation
manual attached to the unit.
• If you perform the test run for all indoor units at once, you cannot detect any erroneous connection, if any, of the refrigerant
pipes and the connecting wires.
* The compressor operation is not available for 3 minutes at least after the power is supplied.
• The compressor can emit noise just after turn on the power supply or in case of low outside air temperature.
About the restart protective mechanism
Once the compressor stops, the restart preventive device operates so the compressor will not operate for 3 minutes to protect
the air conditioner.
OCH480A
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