Daikin FTXM71R2V1B internal temperature sensor (thermistor) overreads

[CoachieRic]

Hi My AC guy just installed a Daikin FTXM71R2V1B. Unfortunately the indoor unit is located in a quite enclosed location and the indoor unit’s internal temperature sensor tends to overread. This means that, after a while the temperature sensor reaches 31c (heating mode), and the unit cycle through/ goes into cooling mode. We tried to fit an external temperature sensor or wired controller but Daikin said that it is not possible to fit with that model. However looking at the PCB diagram there seems to be an option to move the thermistor to another location, away from the hot flow so it does not overreads. Has anyone got experience with that specific model? Either moving the internal thermistor or taking the temperature input from a wired controller (BRC1E63 or equivalent)? Many Thanks

[frank]

The BRC1E63 is not compatible with your model
the correct wired controller is the BRC073 https://www.daikin.co.uk/en_gb/products/brc073.html

Unfortunately, the accessory has a restricted field setting list -including the ability to use a remote sensor, so the information your installer gave is correct.

Don't forget that any unauthorised alterations that you do will null the warranty.

[CoachieRic]

Many Thanks for the reply. Would there be any solution apart from moving the indoor unit?
The BRC1E63 is not compatible with your model
the correct wired controller is the BRC073 https://www.daikin.co.uk/en_gb/products/brc073.html

Unfortunately, the accessory has a restricted field setting list -including the ability to use a remote sensor, so the information your installer gave is correct.

Don't forget that any unauthorised alterations that you do will null the warranty.

[frank]

If you are in 'HEATING' only mode, then the unit should not change over to 'COOLING'.

The temperature sensor reads and then controls on the return air circulating into the unit. How are you measuring 31C at the sensor?

Make sure that only the SUN icon is showing on the controller, not 'AUTO' and set your room temp to, say, 23C then monitor how close the room maintains to 23C over a few hours. Make a log of the mid room temp readings away from the airflow so that the thermometer is not influenced by the unit discharge air, with a decent thermometer (not a £2 one from Aldi etc.)

One way to do it is to put a glass thermometer into a small half full glass of water and then let the glass sit in the room for a few hours while the unit is on. Try not to open and close doors into the room while the test is ongoing.

If your room is fluctuating more than 2K (above 25C) then get on to your installer and complain that the system is not maintaining temp correctly, i.e. floating too far above set point.

[CoachieRic]

16040
Many Thanks again for the reply. I think the issue is that the indoor unit is installed in quite an enclosed location although there is sufficient room around it (please see photo). If I have the swing on, the temperature detected by the sensor rises to 31 C within a couple of minutes. One workaround is to have the swing off whilst blowing the air horizontally (per the photo) and put the unit on heat/ eco mode but even in that situation the sensor rises to 31 C maybe in 10-15 minutes whilst the "real" room temperature is around 20C and the unit stops until the temperature detected goes down by a couple of degrees.
Apparently the thermistor is on the PCB, and one option might be to cover it but as you said it could invalidate the warranty. In fairness the installer are doing their best to help but not sure Daikin have a solution to offer. They say that because it is a residential unit there are no options for external sensor.

[al]

Where are you able to read the internal unit temperature sensor?

Any air hitting the pelmet will bounce back onto the unit, raising its reading. Set the Louvre to highest setting possible to direct air out, fan will cycle off once temperature is reached, this can be programmed out i believe.

[Brian_UK]

If the unit was repositioned to a false wall at the front of that recess you should get better results.

Is that a possible option?

[CoachieRic]

If the unit was repositioned to a false wall at the front of that recess you should get better results.

Is that a possible option?

Guys Thanks for the reply and ideas. We have covered the pelmet at the top of the unit making a nice ramp so the air does not flow back towards the unit. It helped a bit but we don't believe the issue is the air flowing back. We have measured the temperature around the unit when heating, it tends to be around 22 C everywhere apart from the right hand side where the PCB and thermistor are located where it is showing 28-29C near the "intelligent eye". This is the side where the pipework is coming from teh outside and I believe this pipe is running at around 45C. The installer has insulated it carefully but we are still insure why this side of the unit is getting so hot. As you can see from the picture left and right are symmetrical in terms of distance to the wall, etc. It looks like there is somehow a leakage of hot air on the right hand side where the thermistor is located. Any further ideas greatly received!

[frank]

Are the vertical vanes in the air outlet pointing the air straighht out?

[CoachieRic]

Yes they are. Horizontal swing is off. Vertical swing off with the Louvre in the highest possible solution. There is no back flow at all around the pelmet but it looks like the temperature elevation comes from inside the unit. Installer will be back to try to insulate the pipe very neatly but we are running out of ideas.
When the unit is switched on teh temperature goes from say 18C to 30 C in no time. When it's off it says at 28-30C for ages then comes back to 18 after only 20 minutes. It feels like some hot air trapped inside the unit if that makes sense

[frank]

But where and how are you measuring these temperatures, as there is no facility for this on the remote controller?

In heating mode, the louvre should point down to force the hot air to low level, which then naturally rises and causes circulation. If the louvre is at the highest position, you will be throwing the hot air across the ceiling (coander effect) where it will be drawn back into the unit by the fan. All of this without mixing with the cooler air in the room.

Seems like part of your problem is the installation position and the way it is being programmed to operate.

Try to make a temporary 'duct' out of cardboard that will fit over the fan outlet and force the hot air down toward the floor and see if there is any improvement. Use high speed fan for this.

[Tayters]

On your photo does that pelmet create a lip on the inside?
I'm guessing it does and as has been suggested the air blown out is short circuiting. Similar thing happened to me when I fitted a drip tray below a wall mount in a comms room, lip of the drip tray was catching the air and directing it back to the unit.
Can you make the top of that storage unit flat so less chance of air bouncing back?

[CoachieRic]

On your photo does that pelmet create a lip on the inside?
I'm guessing it does and as has been suggested the air blown out is short circuiting. Similar thing happened to me when I fitted a drip tray below a wall mount in a comms room, lip of the drip tray was catching the air and directing it back to the unit.
Can you make the top of that storage unit flat so less chance of air bouncing back?

I have tried to make the top of the cupboard flat using an insulation board so there is no lip between the top of the cupboard and the pelmet. It has not really helped unfortunately, the thermistor is still reading 29-30 C (that's the reading I see on the Daikin app). What really puzzles us is why one side of the indoor unit gets significantly hotter than the other side, all things being symmetrical outside the unit. Even a few minutes after I switched off the unit, I am reading 21 on the left and 40 degrees at least on the right. I will try to post a video

[CoachieRic]

I have posted a video to show the difference in temperature between the two sides of the indoor. There is 15 C difference!

https://photos.app.goo.gl/7nSk7KieeA2pwjKXA

[narkom]

The side of the indoor unit the hot gas enters from is supposed to be hotter.

[redroge]

check the air temps in and out and in cooling mode

[al]

The fan motor is on the right hand side where you are pointing the thermometer, the thermistor i thought was on top right when you opened the panel and exposed the filter?

[Brian_UK]

I have posted a video to show the difference in temperature between the two sides of the indoor. There is 15 C difference!

https://photos.app.goo.gl/7nSk7KieeA2pwjKXA

Now try it with the unit running. You could be measuring radiant heat from the fan motor.