Carrier 42QFD048D8S Service Manual page 111

Are the low pressure protector
Are the low pressure protector
and main control board wired
and main control board wired
Method: Disconnect the plug.
Method: Disconnect the plug.
Measure the resistance of the
Measure the resistance of the
low pressure protector. If the
low pressure protector. If the
protector is normal the value is
protector is normal the value is
o. Does a problem still exist?
o. Does a problem still exist?
Is the valve core of the high
Is the valve core of the high
pressure valve fully opened?
pressure valve fully opened?
Is the indoor fan running
Is the indoor fan running
properly in cooling mode?
properly in cooling mode?
Replace outdoor main board. Does a
Replace outdoor main board. Does a
When the lvel of refrigerant is not
When the lvel of refrigerant is not
sufficient, doe the system function
sufficient, doe the system function
properly after more refrigerant is added?
properly after more refrigerant is added?
Check whether the refrigerant
Check whether the refrigerant
system is functioning properly.
system is functioning properly.
Note: For certain models, outdoor PCB could not be removed separately. In this case, the outdoor electric
control box should be replaced as a whole.
Low pressure protection
Low pressure protection
properly?
properly?
Yes
Is the low pressure
Is the low pressure
protector broken?
protector broken?
Yes
Is the outdoor ambient
Is the outdoor ambient
temperature too low?
temperature too low?
No
Yes
Yes
problem still exist?
problem still exist?
No
No

Reconnect the low pressure protector and main
Reconnect the low pressure protector and main
No
Replace low pressure protector
No
Replace low pressure protector
Yes Stop the unit
Stop the unit
Open the valve core of the high
Open the valve core of the high
No
Please refer to the solution of the "Fan
Please refer to the solution of the "Fan
Speed is operating outside of normal
No
Speed is operating outside of normal
range"malfunction.
range"malfunction.
Troubleshooting 
control board
control board
pressure valve
pressure valve