Panasonic Piping Thermistor Fault

[GavinS]

Hi Guys,
I have a Panasonic ducted reverse cycle air conditioner which I believe has a faulty indoor piping thermistor. It keeps turning itself off every 5 minutes and shows a fault code F4.

I confirmed the fault by disconnecting the thermister on the circuit board and replacing it with a 56K resistor. The A/C appeared to operate ok with a resistor in place of the thermistor, however I'm not sure what the consequences are if I continue to operate it like this. I considered dismantling the Indoor unit to access the thermistor, but after examining the indoor unit, it doesn't appear particular easy to dismantle.

Could someone advise if operating the A/C without the piping thermistor working (as I described above) will have any undesirable effects. Alternately, does anyone have a service manual showing how to dismantle the unit

Model: CS-80E90XP

[Deano240]

The sensor will give some feed back to the outdoor to modulate the expansion valve or some sort depends what this thermistor controls. So in the long run yes it would.

[frank]

Sounds like the sensor is detecting low evaporator temperature and going into frost protection mode.

I would investigate the refrigerant charge to make sure this is OK before suspecting the sensor

[Loops]

The pipe sensor has two main functions
1. Cooling - Frost protection
Check: clean filters; clean fan blades, restrictive ductwork; gas charge etc
2. Heating - Overheat protection and preheat fan control
Check: same as for cooling above really
A 56k resistor equates to approx. +2.5°C
My money would be on poor duct design \ grille selection restricting air flow.
Cheers
Loops