Originally Posted by
ozairman
Before you shell out on a replacement board, the following may help.
The Run light Flashing Timer 4 flash error is not just triggered by the E39 Discharge pipe sensor error logic that narkom explained, it is also triggered by the Discharge pipe sensor disconnection protection control.
This control is trying to detect if the discharge pipe sensor has become disconnected from the discharge pipe itself. The logic is complex but in a nutshell it does this by monitoring the discharge pipe temperature and outdoor air temp and looking at the rate of change the rate of change of the discharge pipe temperature sensor when the compressor is running at various speeds. If the discharge pipe sensor temp does not rise to the target level the unit stops with that error code, so what does this mean in reality?
There are a couple of other scenarios which can trigger the error namely liquid floodback from crossed interconnect wiring and is the first thing that you should rule out (even if its been in for a while, I have come across this on systems that have been in for years). Run each indoor unit on cooling mode for 10-15 minutes and confirm that it's indoor coil is the one that is actually getting the refrigerant flow and not some other indoor unit is starting to frost up. Running them on heating to test is no good as the EEV's in the outdoor for each circuit are partially opened on heating mode.
Once that is ruled out the other scenario can be from low load operation with only one head running. Check with your customer what heads they have running when the error happens, there may be a way around this but I don't have access to the tech manual for that model at the moment.
HTH
regular poster
