Carrier X-POWER Series Service Manual page 155

Carrier service manual
4.9 H7: Quantity of indoor units decrease error (Only display on master unit, all the ODU in standby)
"H7" error will display when the quantity of indoor units decrease above 3 minutes.
H7: Quantity of indoor units
decrease error
Communication terminals P, Q,
E are loose
No
Some IDU are assigned the
same address
No
Some IDU are power off
No
Transformer of IDU is disabled
No
IDU are not unified power supply*
No
485 communication IC is disabled
No
IDU PCB is disabled
Note:
1. How to check whether the transformer of IDU is disabled
The voltage input for IDU transformer is 208-230V, the voltage output of is AC9V (yellow-yellow) and AC13.5V (brown-brown)
2. How to check whether the 485 communication IC is disabled
The normal voltage between "P" and "GND" is DC2.3~2.8V, between "Q" and "GND" is DC2.3~2.8V. If the voltage is out of the
normal range, the 485 communication IC is disabled.
*Indoor units should be unified power supply, which can prevent compressor from liquid hammer caused by dropped indoor
units with EXV unclosed.
Troubleshooting
Yes
Fasten the communication
terminals
Yes
Set the IDU addresses differently
Yes
Power on all IDU
Yes
①
Replace the transformer
Yes
Insure all the IDU be unified
power supply
②
Replace the IDU PCB
①
②
P Q E terminals
R410A DC Inverter Series
173