Panasonic Ducted A/C Fault

[GavinSV]

Hi Guys, Does Austech have any A/C experts? - 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 have confirmed the fault by disconnecting the thermistor 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 to be particular easy to dismantle.

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

The Indoor unit is a Panasonic Model: CS-80E90XP -Cheers

/Gavin

[TVguy]

... I have confirmed the fault by disconnecting the thermistor 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...

Could someone advise if operating the A/C without a working piping thermistor (as I described above) will have any undesirable effects.

Yes, leaving the resistor in place will have undesirable effects as the pipe sensor provides feedback to allow for refrigerant control via the LEV (linear expansion valve).
Did you measure the resistance of the pipe NTC? These are normally about 5 kΩ to 10 kΩ at ambient. Sadly no service manual; check the model number on the outdoor unit for more information.

[GavinSV]

Thanks TVguy,
I eventually got a service manual from a dodgy looking Russian website for 4 euro's. I finally figured out how to dismantle the unit and managed to remove the thermistor. On initial testing, the NTC looked ok and measured approx 30kΩ which was about right for the temperature. However, when I warmed up the thermistor it went open cct. Yee-harrr!! Got the bastard.

The helpful guys at Industrial Air found a suitable thermistor from a similar A/C. SHould have a warm house by tomorrow...

-Cheers

[TVguy]

Thanks TVguy,
I eventually got a service manual from a dodgy looking Russian website for 4 euro's. I finally figured out how to dismantle the unit and managed to remove the thermistor. On initial testing, the NTC looked ok and measured approx 30kΩ which was about right for the temperature. However, when I warmed up the thermistor it went open cct. Yee-harrr!! Got the bastard.

The helpful guys at Industrial Air found a suitable thermistor from a similar A/C. SHould have a warm house by tomorrow...

-Cheers

Well done GavinSV! These NTC are essentially the same device for all AC units but encapsulated in different packages. They tend to go O/C due to mechanical failure of the wire bonding.
Enjoy the warmth.