Mitsubishi Electric PURY-P120, Service Handbook

Page: 220 / 411

[
IX
Troubleshooting ]
- 211 - HWE09130 GB
1. Error Code
Out-of-range outside air temperature
2. Error definition and error detection method
Œ
When the thermistor temperature of -28°C[-18°F] or below has continuously been detected for 3 minutes during heating op-
eration (during compressor operation), the unit makes an error stop and "3121" appears on the display. (Use the OC therm-
istor temperature to determine when two outdoor units are in operation.)
Œ
The compressor restarts when the thermistor temperature is -26°C[-15°F] or above (both OC and OS) during error stop. (The
error display needs to be canceled by setting the remote controller.)
Œ
Outdoor temperature error is canceled if the units stop during error stop. (The error display needs to be canceled by setting
the remote controller.)
3. Cause, check method and remedy
Check the following factors if an error is detected, without drop in the outdoor temperature.
<Reference>
3121
Cause Check method and remedy
(1) Thermistor failure Check thermistor resistance.
(2) Pinched lead wire Check for pinched lead wire.
(3) Torn wire coating Check for wire coating.
(4) A pin on the male connector is missing or
contact failure Check connector.
(5) Disconnected wire Check for wire.
(6) Thermistor input circuit failure on the control
board Check the intake temperature of the sensor with the LED
monitor.
When the temperature is far different from the actual temper-
ature, replace the control board.
TH7
Open detection
-40 C [ -40 F ] and below (130 k )
Short detection
110 C [230 F ] and above (0.4 k )