Emergency Operation - Mitsubishi Electric PRH-P8MYA Technical & Service Manual

[8] Emergency operation

1) When the following check displays occur at the outdoor-side controller board, or when the wired remote controller
or indoor-side controller board microcomputer fails, if there are no other defects, emergency operation is possible
by shorting the connector
• Abnormalities that allow emergency operation
Display
Liquid temp thermistor (TH1) open or shorted
U4
Condenser/evaporater temp thermistor (TH3) open or shorted
E8 Indoor-side/Outdoor -side communication receive abnormal (outdoor-side unit)
E9 Indoor-side/Outdoor -side communication send abnormal (outdoor-side unit)
E0 - E7 Communication other than outdoor-side unit abnormal
2) Check items and precautions when performing emergency operation
a) In addition to the abnormalities above, check the outdoor-side unit for any abnormalities. (When there is an
abnormality other than the above, emergency operation is impossible.)
b) Check the operating range. (For U4 display)
Since the outdoor-side fan always operates at full speed at emergency operation, do not operate the air
conditioner outside the range shown below.
Operation range (outdoor-side unit intake temperature)
Cooling
Heating
c) When performing emergency operation, set the outdoor-side controller board after setting the emergency operation
switch (SWE) on the indoor-side controller board. For the indoor emergency operation method, refer to the
indoor unit wiring diagram.
d) A power failure causes emergency operation to become continuous operation. ON/OFF, temperature adjust-
ment and other operations cannot be performed from the remote controller.
e) Since cool air is discharged from the indoor-side unit, when the outdoor-side unit starts the defrosting
operation during heating emergency operation, do not operate the air conditioner for a long time.
f) You can perform cooling emergency operation up to 10 hours. The indoor-side unit heat exchanger
may freeze.
g) At the end of emergency operation, always return the switch settings, etc. to their original state.
3) Emergency operation contents
a) The operation mode operates according to the contents set (cooling or heating) by SW4-2.
b) The fan operation condition is always 100% operation.
c) The operation mode display flashes every other second.
(CN31) on the outdoor-side controller board.
Check contents
greater than 20 °C
less than 10 °C
- 58 -
Operation outside this range may
cause compressor trouble.