Mitsubishi Electric PUHY-HP120TNU-A, Service Handbook

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[1-4 Precautions for Wiring ]
HWE18240_GB
chapter 1 -
11
1 Check Before Servicing
1-4 Precautions for Wiring
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Control boxes house high-voltage and high-temperature electrical parts.
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They may still remain energized or hot after the power is turned off.
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When opening or closing the front cover of the control box, keep out of contact with the internal parts.
Before inspecting the inside of the control box, turn off the power, leave the unit turned off for at least 10 minutes, and check
that the voltage across pins 1 and 5 of connector RYPN has dropped to 20 VDC or less.
It will take approximately 10 minutes until the voltage is discharged after power off.
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Disconnect the relay connectors (RYFAN 1 and RYFAN 2) on the outdoor unit fan before performing maintenance work.
On (E)P72, disconnect RYFAN1 only.
Before connecting or disconnecting the connector, check that the outdoor unit fan is stopped and that the voltage across pins
1 and 5 of connector RYPN has dropped to 20 VDC or less.
If the outdoor unit fan is rotated by external forces such as strong winds, the main circuit capacitor can be charged and cause
an electric shock.
Refer to the wiring nameplate for details.
Reconnect the relay connectors (RYFAN 1 and RYFAN 2) after completion of maintenance work.
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Before turning on the power, make sure the power-supply wire is properly connected. Also, perform a voltage check at the
power-supply terminal block. (Refer to item (5) in section [6-1 Read before Test Run])
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When the power is on, the compressor is energized even while the compressor is stopped.
It is energized to evaporate the liquid refrigerant that has accumulated in the compressor.
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Before connecting wiring to TB7, check that the voltage has dropped below 20 VDC.
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When a system controller is connected to the centralized control transmission cable to which power is supplied from the out-
door unit (power jumper on the outdoor unit is connected to CN40), be aware that power can be supplied to the centralized
control transmission and the system controller may detect an error and send an error notice if the outdoor unit fan is rotated
by external forces, such as strong winds, even when power to the outdoor unit is turned off.
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When replacing the internal electrical components of the control box, tighten the screws to the recommended tightening
torque as specified below.
Recommended tightening torque for the internal electrical components of the control box
1 When replacing semiconductor modules (e.g., INV board, fan board), apply heatsink silicone evenly to the semiconductor
module on the back of the circuit board. Next, tighten the screws holding the semiconductor module to one-third of the
specified torque, and then tighten the screws to the specified torque.
2 Deviating from the recommended tightening torque may cause damage to the unit or its parts.
Take the following steps to ensure that the screws are properly tightened.
1) Ensure that the spring washers are parallel to the terminal block.
Even if the tightening torque is observed, if the washers are not parallel to the terminal block, then the semiconductor module
is not installed properly.
Screw Recommended tightening torque (N·m)
M3 0.69
M4 1.47
M5 2.55
M6 2.75
M8 6.20
Proper installation
Loose screws
Spring washers are parallel to
the terminal block