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This tech tip video runs through how to trouble-shoot the variable frequency drive (VFD) on a rooftop unit when the blower is not running.
Here are some basic things to check:
Is the wild leg on L3?
Is there an alarm?
- Green LED Flashing
- Alarm condition has happened but the drive will continue to operate.
- Plug in keypad to diagnose alarm.
Is there a fault?
- Red LED flashing
- Fault condition has occurred and the power must turned off for 5 min to reset.
- Plug in keypad to diagnose fault.
Is there a call for the blower?
- Check at thermostat terminals.
- R to G, low speed.
- R to W and R to Y2 high speed.
- Check the low speed and high speed inputs on the drive low voltage terminals.
- Yellow to Blue (DI2 to GND) 24 volts DC low speed call.
- White to Blue (DI3 to GND) 24 volts DC high speed call.
- If no call check the replay board outputs.
- Replace the relay board.
Is there power to the drive?
- Main U1,V1 and W1 should be line voltage.
- If there is no power, check the inline fuses on the 580J/558J 07 to 12.
Is there power to the motor?
Is there power to all legs of the motor?
To bypass the drive, power the unit down.
- Unplug the connectors coming from the control box and plug them directly into the motor leads.
- Make sure to bypass the inline fuses (07 to 12 Units).
Figure 24 is mentioned at the 1:22 mark and figures 25 and 26 are mentioned at the 2:49 mark.
Contact the experts at B-Y with any questions!
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