Haier MVAH018MV2AA Service Manual page 46

Constant air volume duct
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[18] The 4-way valve of 3-pipe valve box reversing failure
If the 4-way valve of 3-pipe 
valve box is internal leakage
Check if the TC1 and TC2 of indoor 
unit are normal, if the resistance is 
right? If the connect well?       
If  the  4-way  valve  of  outdoor 
unit is internal leakage
Replace the driver module, if it is normal
If exceeds the running range of the 
Adjusting the running range
Note: abnormity confirmation conditions
For  MRVIII-RC  system,  the  outdoor  unit  is  running  normally,  when  the  4-way  valve  of  valve  box  is 
power on and its connected heating indoor unit's parameter satisfy following conditions
• &              •  When 4-way valve of valve box is ON
                   • TC2 ≤ CT-20
                   • or              • TC1 ≤ 0
                                       • TC1 ≤ master unit Ps_temp+10
No
Yes
Yes
No
outdoor unit
Yes
o
C lasts for 5min
o
C lasts for 5min
Adjust  it  correctly  by  after-sales 
Yes
personnel on site.
No
Adjust  it  correctly  by  after-sales 
personnel on site.
No
Adjust  it  correctly  by  after-sales 
personnel on site.
Yes
Replace the driver module
If  the  pressure  difference  between 
high  and  low  pressure  less  than 
No
0.4Mpa  before  the  failure  occurs, 
replace the inverter compressor
o
C lasts for 5min
44

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