MCAC-VTSM-2015-09      R410A All DC Inverter V4+S Series 60Hz 
Troubleshooting 143 
4.13   yHd: Slave unit malfunction (y refers to corresponding slave unit) 
yHd is only displayed on the master unit. y stands for corresponding slave unit. If y is 1, it refers No.1 slave unit 
which has malfunctioned. 
 
4.14   P0: Temperature protection of inverter compressor 
4.15   P4: Discharge temperature protection; 
4.16   H6: P4 protection appears three times in 100 minutes 
The error will only display on the faulty unit, all the ODUs will be on standby.   
If H6 error occurs system must be restarted as it cannot automatically resume. 
 
 
 
Note:   
* How to check for the discharge temperature sensor 
Using a multi meter to measure resistance, if the resistance is too low, the sensor has short circuited, if the resistance at certain 
temperature is not consistent with attached table 2, the sensor is disabled 
* The phenomenon of insufficient refrigerant 
Top temperature and discharge temperature of all compressors are higher than normal value, discharge pressure and suction 
pressure are both lower than normal value, current is lower than normal value, suction pipe may be frosting. All the phenomenon 
will disappear after recharging refrigerant. 
Outdoor main PCB is damaged 
Replace the outdoor main PCB 
Insufficient refrigerant caused by 
insufficient recharge or refrigerant 
Add refrigerant or inspect the system 
for leaks 
The low pressure side is blocked, 
caused by crushed or bent pipe, 
closed EXV, closed stop valve, dirty 
filter, etc.* 
Make sure all valves are open, clean 
the filter, if the filter is blocked by ice, 
the system should be cleaned 
The indoor load is too large* 
Make sure the ratio of connectable 
IDU is less than 130% or add ODU 
System contains air or nitrogen* 
Flush all refrigerant. Then vacuum 
the system and recharge refrigerant. 
Add oil to the system if it leaks. 
Discharge temp. sensor has short 
circuited or is disabled*.