Daikin C5 fault but what unit

[marvyn]

Hello Gents
I have a C5 fault showing on a controller that runs two ceiling cassettes so an r3t thermistor fault is likely how can I tell which unit is faulty, they are both short cycling on heating before the pre heat sign shows on controller I've read about checking ohms reading against temp on thermistor plug ie 20 deg c = 24.45 k - Ohms but where am I taking the temp reading from for a comparison. your knowledge and help is appreciated

[Peter_1]

Which type of ceiling cassettes? You should locate R3T on the indoor PCB (it's marked on the PCB in white markings) at 20°C, you should meausere 25 kohm, 22.85 at 22°C and 27.41 at 18°C.
Connect eventually a resistor with a vlau between 40 kOhm and 20 kOhm to test it.
A decadebox is a good device for this.

[gsracer]

Should show the unit number 0 or 1 with the fault code , use mode 43 if you need to check which unit is 0 and 1

[marvyn]

Gsracer the units are not marked up so when in mode 43 what's telling one from the other

[marvyn]

Cheers fellas the Model is FXFQ5OP7VEB couple of more quickies for you both Peter am I getting my temp measurement from the ambient return air or air off or from somewhere on the pipe work

[Tayters]

The temperature you are measuring is whatever the probe is reading. In this case you are reading the larger pipe temp. If the unit has been off for a while or perhaps on fan only then you should be pretty much near room temperature.

If you use mode 43 then the fan should spin round when you select each unit thereby letting you know how they are addressed.
If it gives you jip then might be easier to read ohms from both units, save the farting about, unless of course you like to fiddle.

[marvyn]

Tayters great help that mate much appreciated

[Peter_1]

R3T is connector X17A on the PCB. Disconnect thermistor before measuring.
R1T = X13A
R2T = X12A