Mitsubishi Electric PQHY-P72ZLMU-A Service Handbook page 323

[ IX Troubleshooting ]
2. Phenomena
Although heating operation starts with the normal remote controller display, the capacity is not enough.
(1) Cause, check method and remedy
1. Compressor frequency does not rise sufficiently.
Faulty detection of pressure sensor.
Protection works and compressor frequency does
not rise due to high discharge temperature
Protection works and compressor frequency does
not rise due to high pressure.
The high temperature of the heatsink on the INV
board triggers the protection mechanism that
keeps the compressor frequency from rising.
ON
1 2 3 4 5 6 7 8 9 10
HWE15150
Cause
The figure at left shows that the switches 1 through 5 are set to ON and 6 through 10 are set to OFF.
Check method and remedy
(1) Check pressure difference between the detected
pressure by the pressure sensor and the actual
pressure with self-diagnosis LED.
If the accurate pressure is not detected, check
the pressure sensor.(Refer to the page on Trouble-
shooting of Pressure Sensor)
Note: Higher inlet pressure by the high pressure sensor
than the actual pressure causes insufficient capac-
ity.
SW4 setting (SW6-10: OFF)
High pressure sensor
Low pressure sensor
(2) Check the difference between the condensing tem-
perature (Tc) and the target condensing tempera-
ture (Tcm) with self-diagnosis LED.
Note: Higher Tc than Tcm causes insufficient capacity.
SW4 setting (SW6-10: OFF)
Condensing temperature Tc
Target condensing temperature Tcm
Note: Protection works and compressor frequency does
not rise even at lower Tc than Tcm due to high dis-
charge temperature and high pressure.
At high discharge temperature:
Refer to 1102.
At high pressure:
Refer to 1302.
(3) Fan problem, fan connection fault
Check to see if the fan is rotating while the heat-
source unit is in operation.
If the fan is rotating ->Check the items listed under
4230.
If the fan is not rotating -> Check the fan wires for
proper connection.
If the fan wires are properly connected, check that
the voltage at the connector CN502 on the control
board is 188 V or above (with the heat-source unit
in operation). If this value is normal, there is a prob-
lem with the fan.
- 314 -
SW4
ON
1 2 3 4 5 6 7 8 9 10
SW4
ON
1 2 3 4 5 6 7 8 9 10
SW4
ON
1 2 3 4 5 6 7 8 9 10
SW4
ON
2 3 4 5 6 7 8 9 10
1
GB