Daikin ducted system blowing cold air sometimes when set to Heat ?

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LostBoyNZ

584 posts

Ultimate Geek

#320124 8-Jul-2025 22:23

I wonder if anyone else with a ducted system has this happen? When it's set to heat only, Auto fan speed, and setback is disabled, once it reaches tempreture I can feel cold air coming from all the ducts. It's not something that just continues for a few minutes, it goes longer.

It looks like we have a Daikin BRC1E63 wired remote controller.

fe31nz

1229 posts

Uber Geek

#3392233 9-Jul-2025 00:00

How cold was it outside? Heat pumps have a temperature range a bit above 0 C (around 2-3 C if I remember correctly) where they tend to accumulate frost. When they detect frost, they have to get rid of it and the way they do that is to reverse the heat pump so it is cooling the room and heating the coils in the outside unit until the frost evaporates. They will then switch directions again and a good heat pump will put in a burst of heat to compensate for the period of cooling. The cooling is usually done quite gently (slow fan). A defrost will not keep on going and usually takes only a few minutes, but under the wrong conditions it can frost up again fairly soon and have to do another defrost.

Another thing that happens is if you have manually set the fan speed and the heat pump has reached the setpoint temperature and it is no longer producing heat. Some (badly progammed) heat pumps will leave the fan running at the locked speed setting. So you get air circulation but no heat added to the air, and some of the cooler air lower down in the room will be moving around and you can feel that. Good heat pumps (in my opinion) will shut down the fan to a minimal speed (required to run air over their temperature sensor) until they need to add more heat, and will then bring the fan up to the specified speed again.

timmmay

20579 posts

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#3392242 9-Jul-2025 07:34

This is standard behavior for Daikin ducted heat pumps. The installer can use the field settings to turn off the continuous fan for heating and cooling individually. It's quite fiddly to do, the documentation isn't widely shared, and if you mess it up you could break the heat pump, so best have your installer do it. It shouldn't take them long. I had an installer teach me how to do it for my heat pump, but I'm very, very careful doing it.

The same field settings let you change things like static pressure - I think that's what it's called. Basically, how hard the fans blow. On my heat pump you can set it from 1 to 15, 1 being low power 15 being high power. There are many other field settings, I don't know what they all do.

HowickDota

423 posts

Ultimate Geek

#3392244 9-Jul-2025 07:50

As above, the field settings can be adjusted to change the fan behaviour when the unit reaches set point.

Edit: (This is for a FBAXXXBVMA/BAVMA model if you can share your indoor unit model the setting codes may be different.)

Mode 21 first code 2 second code set to 02 and mode 22 first code 3 second code set to 02.

LostBoyNZ

584 posts

Ultimate Geek

#3392245 9-Jul-2025 07:59

Thanks so much guys! It was around 8 degrees outside yesterday when it was happening. It sounds like exactly what you guys are saying, that the fan is still running without heat being generated. I'll check out what the field settings are set to this evening, and then will ask the installer if they can come by and change them :)

timmmay

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#3392247 9-Jul-2025 08:05

We found "STOP" better than extra low. I think the theory is with the fan on the thermostat will reflect the room temperature better, but with our system and the Airtouch with wall temperature sensors rather than using a temperature in the return vent that doesn't matter for us.

LostBoyNZ

584 posts

Ultimate Geek

#3392308 9-Jul-2025 10:56

Interesting!

I think our sensor is currently set to the return vent at the moment.

LostBoyNZ

584 posts

Ultimate Geek

#3392517 9-Jul-2025 21:26

My indoor model is FBA60BAVMA, and I just checked the Field Settings :)

For Mode 21, 2 is set to 01

For Mode 22, 3 is set to 01 and 6 is set to 02

I also saw Outdoor Unit Status, where Th1 was 9°C, Th2 was 8°C and Th3 was 55°C, and for Indoor Unit Status, Th1 was 17°C, Th2 was 42°C and Th3 was 44°C.

I was curious what Th3 is, since it's so high, and according to Google's AI (so may not be trust worthy) it's the typically ambient air temperature sensor, but either that's very faulty or not the case with this model :o

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timmmay

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#3392518 9-Jul-2025 21:43

Don't mess with it if you're not 100% sure what you're doing.

LostBoyNZ

584 posts

Ultimate Geek

#3392520 9-Jul-2025 21:52

Absolutely yeah, I'll leave any changes to our installer.

fe31nz

1229 posts

Uber Geek

#3392525 9-Jul-2025 22:34

LostBoyNZ:

My indoor model is FBA60BAVMA, and I just checked the Field Settings :)

For Mode 21, 2 is set to 01

For Mode 22, 3 is set to 01 and 6 is set to 02

I also saw Outdoor Unit Status, where Th1 was 9°C, Th2 was 8°C and Th3 was 55°C, and for Indoor Unit Status, Th1 was 17°C, Th2 was 42°C and Th3 was 44°C.

I was curious what Th3 is, since it's so high, and according to Google's AI (so may not be trust worthy) it's the typically ambient air temperature sensor, but either that's very faulty or not the case with this model :o

Anything in the 50-55 °C range is likely to be a sensor directly in the airflow out of the heat pump coils. For safety reasons, most heat pumps are set to only heat the air to something in that range, and they then mix that hot air into the room to heat it. It is a good check on the health of a heat pump to measure that particular temperature. If it falls below that temperature when the heat pump is working hard, then it is likely that it has developed a refrigerant leak or some other nasty fault. But that is for indoor units in heating mode, or outdoor units in cooling mode. If it is really a temperature on an outdoor unit in heating mode, then it could be the temperature of the refrigerant on its way inside. That should be slightly higher than the wanted air temperature out of the inside unit.

HowickDota

423 posts

Ultimate Geek

#3392600 10-Jul-2025 08:23

LostBoyNZ:

My indoor model is FBA60BAVMA, and I just checked the Field Settings :)

For Mode 21, 2 is set to 01

For Mode 22, 3 is set to 01 and 6 is set to 02

I also saw Outdoor Unit Status, where Th1 was 9°C, Th2 was 8°C and Th3 was 55°C, and for Indoor Unit Status, Th1 was 17°C, Th2 was 42°C and Th3 was 44°C.

I was curious what Th3 is, since it's so high, and according to Google's AI (so may not be trust worthy) it's the typically ambient air temperature sensor, but either that's very faulty or not the case with this model :o

It varies by unit and you normally cant find this in service manuals but it's likely that Th1 is outdoor air temp, Th2 is outdoor heat exchanger temp, Th3 is discharge pipe temp.

For the indoor Th1 return air temp, Th2 supply air temp, Th3 indoor heat exchanger temp.

Discharge temperature can go up to 110C before triggering a fault.

tweake

2391 posts

Uber Geek

#3393334 11-Jul-2025 17:38

sorry to jump in late here,

first thing i would do is get a meter and test the air temp coming out of the vents. moving air feels colder than it actually is. thats why normal heat pumps turn the fan off on the heating but not on cooling. it will also tell you a number you can work with.

if its actually cold, then need to look at how outside air is being sucked into the system, assuming its not done on purpose for ventilation. very common to have duct leakage due to poor installs. leaks on the return will suck in air, while leaks on the outlet side will pump house air outside, which in turn means the house will suck in cold outside air. not uncommon to have both happening.

LostBoyNZ

584 posts

Ultimate Geek

#3393335 11-Jul-2025 17:46

Thanks guys, that's interesting regarding the sensors, and that the discharge temp can go so high without triggering a fault! It sounds like those are probably all as expected then :)

No worries tweake, that's a good point about air feeling colder because it's moving. I've got a little temp/humdity sensor, so I can certainly check that this weekend.