thermo king 404a problem

[andyc425]

problem with thermo king magnum 575, unit keeps shutting off on alarm 56 compressor temp too high now the sensor on the display reading high pr temp read at 130 degrees cesius for the discharge line when unit is off indicating for one that the board is faulty considering i disconnected the sensor but still the board reads temperature. these were the Readings taken whilst running manually with compressor on ,evaporator low speed, injection valve on, condenser fan on, digital valve off

Supply temp- 1.1 degree Celsius
Return temp – 8.7 deg cel
Ambient temp – 30 deg cel
Suction pressure – 70 / -2 degrees celcius
head pressure - 360 psi / 55 degrees celsius at reciever

[Brian_UK]

If you still get a temperature reading with the sensor disconnected it says to me that the sensor is faulty.

[andyc425]

i think you me the relay board , in any case i removed the sensor for the compressor protection and verified the resistance for the given temperature and it was in range. i then proceeded to rewire each sensor into there own individual plugs instead of one so i could input them one at a time to see what was happening. i found out that the condenser temp sensor and compressor temp sensor were some how conflicting and causing the display to read the wrong temperature, i found that if i removed both sensors and left supply and return sensors in i could run the unit, which i did and it came down to - 20 setpoint no problem even though it displayed 2 alarms for the open circuits for the senors. Having discussed the issue with a field manager from thermoking he directed me to change the connecting cables between relay board and controller having done this i found that one cable was causing the malfunction luckily i had a spare unit i could take from. I dont know exactly how it was causing the malfunction i checked resistance on both ends checking for continuity and found no faults but never the less replacing it worked i now get the correct reading on the sensors and the unit is running.