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The basic principle applies when the outlets of two fans share the same duct. If one fan spins significantly faster than the other, the resulting pressure difference drives the slower fan to accelerate until its speed matches that of the faster fan. At this point, the slower fan enters a generator mode, feeding energy back into the VFD and causing the VFD's DC bus voltage to rise. If the voltage reaches the over-voltage stall threshold, the VFD controlling the slower motor automatically increases its output frequency to match the actual rotational speed. Consequently, the fan exits generator mode and returns to motor mode; it stops generating power, and the VFD's DC bus voltage drops.

Troubleshooting for UPS Fault Code 65, Applicable Model: HT(R)X 01-20KVA S L
Q: The UPS displays fault code 65 and fails to start normally. According to the user manual, this fault indicates low battery voltage. How should we troubleshoot this issue?

A: When this series of UPS triggers fault code 65, the control logic will prevent normal startup. This fault is mainly caused by three factors: faulty UPS charger, damaged batteries, or abnormal battery voltage detection circuit.
Please follow the steps below to locate the root cause:
1.Check the actual battery voltage and confirm whether it matches the value displayed on the UPS screen, so as to determine whether the fault originates from the detection circuit on the power board.
1）If consistent:
Disconnect the two battery BUS cables connected to the UPS power board and restart the UPS. Next, measure the DC voltage at the battery BUS cable terminals on the power board to verify whether the measured voltage is roughly equal to the reading shown on the UPS screen and check if the UPS can start normally.
NOTES:
Make sure to discharge the capacitors at these terminals before disconnecting or reconnecting the battery BUS cables.
2）If inconsistent: The battery voltage detection circuit on the power board may be damaged, which requires replacement of the power board.

1. Due to the current limitation of the UPS cabinet back board, only one interface of one BAU can be connected to the module back board of one UPS cabinet.
2. It is recommended to connect the working input terminal of BAU to the output N terminal of UPS, rather than the main input N terminal of UPS, to prevent the disconnection of the N wire in the UPS circuit (such as turning off the output switch of UPS, the N wire of UPS will be disconnected), which may cause interruption of the N wire on BAU and result in abnormal voltage sampling of BAU, causing damage to BAU during operation.
3. The standard voltage version of BAU is currently applicable to power modules of PM25X, PM30X, PM40X, and PM50X.

The SPC5K5TR40 IGBT is broken. In theory, 12028-00021 should be used, but feedback indicates there is no stock. Can I use 12028-00008 as a replacement in hardware?
A: The sizes of the electrical component heat sinks for these two part numbers are the same, so they can be substituted as long as the dimensions match.

1. Check if the VFD is still lighting up. If not, you’ll need to replace the VFD board.
2. Check the RS485 cable between the main control board and the VFD board to see if it’s loose.

 1: Check if the control module's power supply is normal. The indicator flashing means two possible reasons: 1. The power supply is not reaching 220V, 2. There is a short circuit in the devices connected to the control module. Test each of the devices one by one to troubleshoot.

1. Check if the outdoor fan can work.  
2. Use manual control logic to adjust the outdoor fan speed, from low to high, and see at what speed the outdoor fan fault alarm appears. Then check if there is any rubbing between the fan and the guide vane ring.

A: 1. Use a pressure gauge to check the pressure inside the copper pipe to see if the alarm is caused by a lack of refrigerant.
2. Check if the indoor fan switch is turned off, which can cause the cooling to accumulate on the evaporator and make the evaporator temperature too low.

1. Check the IP settings of the control module. The main cabinet must be set to 1, and the following sub-cabinets must be set in the order of 2, 3, 4.
2. Check if the wiring between the cabinets is correct.