Outdoor unit fan always runs even when indoor unit is off. I have disconnected all control wires from the headunit (at the outdoor end to rule out faulty signalling). The fan runs all the time, with just the supply wires connected. All connections to the unit are correct. Any ideas??

14.2.2 To Make a Diagnosis1 Timer LED starts to blink and the unit automatically stops the operation.
2 Press the CHECK button on the remote control continuously for 5 seconds.
3 "- -" will be displayed on the remote control display.
Note: Display only for "- -" (No signal transmission, no receiving sound and no Power LED blinking)
4 Press the TIMER ? or ? button on the remote control. The code "H00" (no abnormality) will be displayed
and signal will be transmit to the main unit.
5 Each press of the button (? or ?) will increase error code
number and transmit error code signal to the main unit.
6 When the latest abnormality code on the main unit and
code transmitted from the remote control are matched,
Power LED will light up for 30 seconds and a "beep" sound
(continuously for 4 seconds) will be heard. If no codes are
matched, Power LED will light up for 0.5 seconds and no
sound will be heard.
7 The breakdown diagnosis mode will be canceled unless
pressing the CHECK button continuously for 5 seconds or
operating the unit for 30 seconds.
8 The LED will be off if the unit is turned off or the RESET
button on the main unit is pressed.
Diagnosis
display Abnormality / Protection control Abnormality
Judgement Emergency operation Primary location to verify H00 No abnormality detected - Normal operation H11 Indoor / Outdoor abnormal communica
tion > 1 min after starting
operation Indoor fan operation
only • Internal / external cable connections
• Indoor / Outdoor PCB H14 Indoor intake air temperature sensor
abnormality Continue for 5 sec. - • Intake air temperature sensor (detec
tive or disconnected) H15 Outdoor compressor temperature sensor
abnormality Continue for 5 sec. - • Compressor temperature sensor
(detective or disconnected) H16 Outdoor Current Transformer open cir
cuit - - • Outdoor PCB
• IPM (Power transistor) module H19 Indoor fan motor mechanism locked 7 times occurance
continuously - • Indoor PCB
• Fan motor H23 Indoor heat exchanger temperature sen
sor abnormality Continue for 5 sec. O
(Cooling only) • Heat exchanger temperature sensor
(detective or disconnected) H24 Indoor heat exchanger temperature sen
sor 2 abnormality Continue for 5 sec. - • Heat exchanger temperature sensor
(detective or disconnected) H27 Outdoor intake air temperature sensor
abnormality Continue for 5 sec. O • Outdoor temperature sensor (detec
tive or disconnected) H28 Outdoor heat exchanger temperature
sensor abnormality Continue for 5 sec. O • Outdoor heat exchanger temperature
sensor (detective or disconnected) H30 Outdoor discharge air temperature sen
sor abnormality Continue for 5 sec. - • Outdoor temperature sensor (detec
tive or disconnected) H33 Indoor / Outdoor wrong connection - - • Indoor / Outdoor supply voltage H38 Indoor / Outdoor mismatch (brand code) H50 Ventilation motor abnormality 7 times occurance
continuously - • Indoor PCB
• Ventilation motor H51 Nozzle lock abnormality 2 times occurance
continuously - • Nozzle H52 Limit switch abnormality - - • Indoor PCB H97 Outdoor fan motor mechanism locked 2 times occurance
within 30 minutes - • Indoor PCB
• Fan motor H98 Indoor high pressure protection - - • Air filter dirty
• Air circulation short circuit H99 Indoor heat exchanger anti-freezing pro
tection - - • Insufficient refrigerant
• Air filter dirty F11 Cooling / Heating cycle changeover
abnormality 4 times occurance
within 30 minutes - • 4-way valve
• V-coil F90 PFC control 4 times occurance
within 10 minutes - • Voltage at PFC F91 Refrigerantion cycle abnormality 2 times occurance
within 20 minutes - • No refrigerant
(3-way valve is closed) F93 Compressor rotation failure 4 times occurance
within 20 minutes - • Compressor F95 Cool high pressure protection 4 times occurance
within 20 minutes - • Outdoor refrigerant circuit F96 IPM (power transistor) overheating pro
tection 4 times occurance
within 30 minutes - • Excess refrigerant
• Improper heat radiation
• IPM (Power transistor) F97 Outdoor compressor overheating protec
tion 4 times occurance
within 10 minutes - • Insufficient refrigerant
• Compressor F98 Total running current protection 3 times occurance
within 20 minutes - • Excess refrigerant
• Improper heat radiation F99 Outdoor Direct Current (DC) peak detec
tion 7 times occurance
continuously - • Outdoor PCB
• IPM (Power transistor)
• Compressor

Note:
"O" - Frequency measured and fan speed fixed.
The memory data of error code is erased when the power supply is cut off, or press the Auto Switch until "beep" sound heard following by pressing the "CHECK" button at remote controller.
Although operation forced to stop when abnormality detected, emergency operation is possible for certain errors (refer to Error Codes Table) by using remote controller or Auto Switch at indoor unit. However, the remote controller signal receiving sound is changed from one "beep" to four "beep" sounds.

No one here.

I'm not sure if the thermostat is wired correctly. First, the thermostat is wired directly to the outdoor unit (compressor/condenser unit). It is NOT directly connected to the indoor unit. It connects to a low voltage control panel in the outdoor unit that sends a signal to your indoor fan/evaporator. This wire is called the fan relay switch and physically runs between the low voltage controls of the indoor and outdoor units. If the fan relay is bad it's possible that the unit runs continuously. To prevent destroying your outdoor unit there is a safety feature that prevents the indoor fan from shutting down while the outdoor unit is running. If the indoor fan did shut down while the outdoor unit was running than you would slug your compressor. That is, your compressor normally sees refrigerant gas but is instead seeing refrigerant liquid. That would not be good since this scenario would destroy your compressor. It sounds like a faulty fan relay. The actual contactor portion of the relay is in the outdoor unit.

Signal transmission error. Indoor and outdoor PCB's cannot communicate. Usually a faulty controller board in the outdoor unit. If the indoor unit otherwise functions normally (can control fan speed, louvres, beeps in replay to all remote buttons) then it is probably OK so check outdoor controller PCB.

check to be sure that both indoor and outdoor fans are running, as is the compressor. examine the tubing for any signs of a leak, or faulty shrader valves (look similar to tire valve, but metal) the indoor unit can run even without the outdoor unit, check all breakers and disconnects.
too many possibilities to diagnose on this limited description, sorry

Possibly a bad control board in the outdoor unit. Pull the disconnect outside to stop machine, wait 10 seconds and out back in. White mist was likely frost built up on indoor coil due to condenser running without the fan.

If you need further help, reach me via phone at https://www.6ya.com/expert/thomas_092728000e6acb79

P8-Abnormality in outdoor unit.
1) Wrong wiring of indoor/outdoor
connecting wire
2) Reversed phase
3) Protection device is working
4) Damaged outdoor coil thermistor

Solution:

1) Check the indoor/outdoor connecting wire.
2) Change the connection of electric wiring.
3) Check the protection device.
4) Measure the resistance of the outdoor coil thermistor.
If the resistance is normal, replace the
outdoor controller board.

Hope,it's helpful.

THE OUTDOOR UNIT HAS A CONTACTOR WITH THE CONTACTS WELDED TOGETHER THE CONTACTOR CONNECTS TO THE COMPRESSOR AS IT TYPICALLY PULLS A SURGE OF 20 -30 AMPS OR MORE..WITH THE INDOOR UNIT IN FAN ONLY THE COMPRESSOR SHOULD NOT BE RUNNING. THE CONTROL WIRES GOING TO THE UNIT HAVE 24 VOLTS TO THE CONTACTOR TO PULL IN THE CONTACTS TO SUPPLY 220 TO COMPRESSOR.

check the wiring diagrams on the panels...

You have not said what model this is for. But as a rule, you have indoor to outdoor wiring, if you open the indoor unit they are labelled 1,2,3,4,5. The indoor wiring must correspond to the outdoor unit. So whatever is wired to 1 indoor must be same on outdoor.