We have a far-let LED flashing 1 second on 1 second off repeatedly indicating a communication error between the indoor and outdoor units. The practical outcome is that the outside condenser doesn't kick on. Our service company has tried it all from going through the process recommended to installing a new "mother board". It still doesn't work. Any ideas?

Serial communication error. This means that the indoor unit is not communicating with the outdoor unit usually because the outdoor unit is faulty. You can check the indoor unit by switching it to 'fan' mode and seeing if all functions work normally (fan speed, louvers move as directed). If it responds normally, then it's probably ok so you can turn your attention to the outdoor unit. A common problem with the outdoor controllers is that they are susceptible to bugs, geckos, etc. shorting them out which will mean replacement of the board.

Hi Charity, F1 is a communication fault, I hope this helps......... CHEERS..
1?Check whether the connection of the outdoor unit and indoor unit is one to one, otherwise connect the L, N and communication line of the indoor unit and outdoor unit one to one.
2?Measure whether the voltage between the zero line and the communication line is 18V-30AC half-wave signal, check whether the communication circuit on the indoor and outdoor electric control board has been damaged, otherwise replace it.
3?Check whether the LED on the outdoor power board has been on, otherwise replace the electric control board.
4?Check whether the unit is abnormal caused by the external interference, if it is, then find the interfering source, and removes it.
http://www.chigo.bg/resources/pdf/Failure-code-manual.pdf

fujitsu is a good brand.
try one of these two things:

Turn the unit off then on again. After that press test button on remote control (rear side) and look how many times now operation and timer LED flashes. Note that. Then press MANUAL/AUTO button on indoor unit until you hear 3 beeps from buzzer. That will erase error memory.
Switch off and than on unit and see if indication repeat or it is gone. If it is gone, keep using your unit.
If it is repeated post your notes here.

OR+++++++++++++++++++++FOR OTHER MODELS

5 x Operation flash and a constant Timer flash indicates an outdoor unit control error. With this code flashing on the indoor unit, you need to point the remote at the unit and push the test run button. The flash pattern will change to a continuously flashing Operation light and a number of flashes of the timer light which gives more detail on what the error is.

To get the unit to try to restart you need to push and hold the manual/auto button on the indoor unit for a few seconds then reset the mains power supply but leave it off for a minute or so for the unit to power down completely. If you are going to try this make sure you make a note of any error codes first if you have to get someone out to look at it, it will help them a lot.

Please mark this answer helpful.

Operation =
Flashing Display Timer = Yes
Turbo =
LED Display = E1
Explanation and Checking points = Indoor unit room thermistor error - Open or Closed Circuit - Check and replace if required

Operation = Yes
Flashing Display Timer = Yes
Turbo =
LED Display = E2
Explanation and Checking points = Indoor unit pipe thermistor error - - Open or Closed Circuit - Check and replace if required


Operation =
Flashing Display Timer =
Turbo = Yes
LED Display = E3
Explanation and Checking points = Indoor unit fan motor malfunction - Check and replace if required


Operation =
Flashing Display Timer = Yes
Turbo = Yes
LED Display = E6
Explanation and Checking points = EPROM error - Check and replace PCB if required


Operation = Yes
Flashing Display Timer = Yes
Turbo = Yes
LED Display = Flashing
Explanation and Checking points = Option code error - Check and input new option code if required via wireless remote controller


Operation = Yes
Flashing Display Timer =
Turbo = Yes
LED Display =
Explanation and Checking points = Outdoor unit temperature sensor - Open or Closed Circuit - Check and replace if required

Serial signal (reverse) error, at operation start up. Usually a faulty outdoor controller board but this one has about six PCB'S in the outdoor unit so your going to need a tech to look at it.

The thermostat is the only communication between indoor and outdoor units.

AHX18MEV
4 - 12
[8] SELF-DIAGNOSIS FUNCTION
1. Indoor unit
(AH-X18MEV, AH-X18MEV-1, AH-X24MEV, AH-X24MEV-1)
To display the self-diagnosis, hold down the AUX button for over 5 seconds on the indoor unit when the indoor unit is not operating.
• The operation lamp (red), timer lamp (orange) and Super jet lamp lighter) flash to indicate the information of malfunction.
(Display of self-diagnosis result)
The operation lamp (red) and the Super jet lamp (green) flash in synchronization with the timer lamp (orange).
(AH-XP18MV, AH-XP18MV-1, AH-XP24MV, AH-XP24MV-1)
To display the self-diagnosis, hold down the AUX button for over 5 seconds on the indoor unit when the indoor unit is not operating.
• The POWER CONSUMPTION indicator indicates the information of malfunction by showing the main category error (number) and the sub-category
error (-number) alternately in 1-second intervals.
Example: Compressor high-temperature error
Remark

AHX18MEV
4 - 12
[8] SELF-DIAGNOSIS FUNCTION
1. Indoor unit
(AH-X18MEV, AH-X18MEV-1, AH-X24MEV, AH-X24MEV-1)
To display the self-diagnosis, hold down the AUX button for over 5 seconds on the indoor unit when the indoor unit is not operating.
• The operation lamp (red), timer lamp (orange) and Super jet lamp lighter) flash to indicate the information of malfunction.
(Display of self-diagnosis result)
The operation lamp (red) and the Super jet lamp (green) flash in synchronization with the timer lamp (orange).
(AH-XP18MV, AH-XP18MV-1, AH-XP24MV, AH-XP24MV-1)
To display the self-diagnosis, hold down the AUX button for over 5 seconds on the indoor unit when the indoor unit is not operating.
• The POWER CONSUMPTION indicator indicates the information of malfunction by showing the main category error (number) and the sub-category
error (-number) alternately in 1-second intervals.
Example: Compressor high-temperature error
Remark

3. CHART
<INDOOR UNIT> ?:1-second ON / 1-second OFF
Problem
symptom
Outdoor
unit indication
(LED1)
Indoor unit Malfunction
No.
Content of diagnosis Check point Action
Lamp Main Sub Main Sub
Normal
condition
Normal
blinking
? ? ? ? ? Timer (Orange) 0 0 Normal
Operation (Red)
Super Jet (Green)
Indoor and
outdoor
units do not
operate.
1-time ? ? ? ? ? Timer (Orange) 1 0 Outdoor unit
thermistor
short-circuit
Heat exchanger
thermistor short
circuit error
(1) Measure the resistance
of the outdoor
unit
thermistors.
(1) Replace the outdoor
unit thermistor
assembly.
? Operation (Red)
Super Jet (Green)
? ? ? ? ? Timer (Orange) 1 Outdoor temperature
thermistor
short circuit error
(2) Check the lead wire
of the outdoor unit
thermistor for torn
sheath and shortcircuit.
(2) Replace the outdoor
unit thermistor
assembly.
? Operation (Red)
? Super Jet (Green)
? ? ? ? ? Timer (Orange) 2 Suction thermistor
short circuit
error
(3) No abnormality
found in above
inspections (1) and
(2).
(3) Replace the outdoor
unit control
PWB assembly.
? Operation (Red)
? Super Jet (Green)
? ? ? ? ? Timer (Orange) 3 2-way valve
thermistor short
circuit error
? Operation (Red)
? ? Super Jet (Green)
LED1
AU-X24MV, AU-X24MEV
AU-X18MV, AU-X18MEV
LED1

I'm not sure exactly what unit you have and what controls you have installed on the unit. But....there usually is a flash code schematic on the unit. Usually on the inside of the blower compartment cover. This should tell you what is wrong with the unit. It could have a low voltage short somewhere and is loosing the call for cool. So the answer can be a possible yes to your question but without knowing the flash code, it's hard to tell from my point of view. You might end up calling a service professional out to check it.

Recheck the wiring. Pay special attention to the wiring splices with those triangular doo dads on them.. that is where my issue was! Wires was just eaten away by the elements.