10) Temperature cutoff protection
confirm the malfunction 
according to the fault code list
yes
yes
no
yes
no
yes
no
yes
no
yes
no
Replace sensor
yes
Replace indoor PCB
Are indoor sensors for 
ambient temperature and 
coil properly located?
Is resistance of indoor 
sensor correct?
Does four-way 
valve work 
properly?
Relocate
Replace four-way 
valve
Is outdoor four-way valve 
in good condition during 
heating cycle?
Does small relay coil 
of four-way valve have 
a voltage of 12V DC?
no
Relay is broken. 
Replace PCB
Is indoor unit 
malfunction caused by 
lack of refrigerant?
charge refrigerant
Is heat exchange effect 
adversely affected by heavy dust 
in indoor and outdoor units?
cleaning
Commercial Air Conditioner Model: AP*****EAA AU*****EAA 
37