Mitsubishi Heavy Industries SRK20HD-S Technical Manual page 26

(7) Compressor Overheat Protection
If the discharge pipe temperature (sensed by Th6) exceeds the set temperature value, the compressor stops. If the temperature is 95ºC
or lower after a 3-minute delay, it starts again, but if this function is reactivated again within 60 minutes, it results in an abnormal stop.
(8) Serial signal transmission error protection
(a) Purpose: Prevents malfunction resulting from error on the indoor ↔ outdoor signals.
(b) Detail of operation: When the indoor unit controller ↔ outdoor unit controller signals cannot be received, the compressor
is stopped immediately. Simultaneously, the red LED on the printed circuit board of outdoor unit controller flashing 6 times
for 0.5 second at intervals of 8 seconds. Once the operation stops, it does not start any more.
(Timer lamp on the indoor unit flashing at the same time.)
(9) Thermistor disconnection (room temperature, indoor heat exchanger, outdoor temperature, discharge pipe)
(a) Room temperature thermistor
If the temperature detected by the room temperature thermistor is –20ºC or lower continuously for 15 seconds or longer while
operation is stopped, an error indication is displayed.
(b) Indoor heat exchanger thermistor
If the temperature detected by the indoor heat exchanger thermistor is –20ºC or lower continuously for 15 seconds or longer
while operation is stopped, an error indication is displayed.
Also, if the temperature detected by the indoor heat exchanger thermistor is –20ºC or lower continuously for 3 minutes after
heating operation has started, the indoor unit's fan speed is forcibly raised to speed 5. After this, the air conditioner is stopped
if the detected temperature remains at –20ºC continuously for 40 minutes.
(c) Outdoor heat exchanger thermistor
If the temperature detected by the outdoor heat exchanger thermistor is –50ºC or lower continuously for 15 seconds or longer
while operation is stopped, an error indication is displayed.
Also, the air conditioner is stopped if the temperature detected by the outdoor heat exchanger thermistor remains at –50ºC or
lower continuously for 40 minutes after heating operation has started.
(d) Outdoor temperature thermistor
If the temperature detected by the outdoor temperature thermistor is –40ºC or lower continuously for 15 seconds or longer
while operation is stopped, an error indication is displayed.
(e) Discharge pipe thermistor
After the compressor has operated for 9 minutes continuously, if there is a disconnected signal for the discharge pipe ther-
mistor detected temperature for 15 seconds (less than 7ºC), the compressor stops. After a 3-minute delay, it restarts, but if an
abnormality is detected 4 times continuously, the air conditioner is stopped fully and an error indication is displayed.
Operation possible
Abnormal stop
95 125
Discharge pipe temperature (˚C)
24
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