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spaceman347
04-07-2012, 09:42 AM
I have a Daikin ducted AC system model FDYQ180M (outdoor unit - RZYQ7PY1) installed in a 180sqm house. It is stamped with a manufacture date of Nov 2011.

This is my first winter with it and when the overnight temp drops below +2 C the system ices up very badly and is not able to clear the ice during the defrost cycle. The ice clears from the top of the fins but the bottom 40 - 50cm or so never melts.

Once the ice blocks up the drain holes in the bottom tray the melt water from the defrost cycle has nowhere to go and the problem spirals.

The only way that I am able to clear the ice is to shutdown the system and melt it by pouring warm water over it. This includes the piping inside the external unit which develops extremely thick layers of ice.

The attached pic was from a night where the temps got down to approx -4C and I had gone out the previous night at 10pm with buckets of warm water and melted off all the ice so this formed in approx 8 hrs. (sorry about the size, I don't seem to be able to make it any smaller)

9088

I have had the service agent out many times now, he has replaced the system board and temp sensors, and weighed the refrigerant and can not find anything wrong.

Does anyone have any ideas of what could be wrong? Could the refrigerant pipes at the bottom of the unit be blocked, thereby not allowing the defrost cycle to melt the ice from the bottom of the fins?

padraic
04-07-2012, 07:57 PM
needs more gas... has it a long pipe run from outdoor to indoor.. are all the outdoor fans going when cold out

ncabral
04-07-2012, 08:01 PM
hello you donīt have a lot of air circulation in out door unit and then you have to look the *****

stufus
04-07-2012, 08:21 PM
What's the humidity when it's 2c....
The melt water is being trapped by the Ice at the very bottom of the coil as the bottom pass is about 25mm off the unit base .As this never melts it creates an ice bridge between the coil and the coil guard and the cycle repeats every defrost and compounds the issue .
Daikin do a heater which can be retrofitted to the base of the unit.
Cheers
Stu

spaceman347
04-07-2012, 10:19 PM
The service agent who has been out on 5 or 6 occasions now says that he has checked the gas and the charge amount is right (or so he says). The distance between the indoor and outdoor unit is approx 12-15m.

There is only 1 fan on the outdoor unit (on the top) and it seems to be operating fine.

Stu: Your description sounds logical, this definitely seems to be what is happening. According to our official weather site, the humidity is up around 80-90% during the low temps so I guess they are difficult circumstances for the system to operate in.

I've also noticed that the coils do not frost/ice up evenly which doesn't seem logical to me (not that I know much about how they work).

Why would the coils frost up in bands like this, does the refrigerant not flow through them all evenly?

9091

stufus
04-07-2012, 11:00 PM
They can frost up as pictured , It all depends on the coil configuration and the position of the headers and/or distributors ,and the load senario.
But unless that photo is deceiving , that unit looks very close to the wall and could be suffering from air flow issue's.
I hope there is no overhang above the fan outlet causing short cycling.
Cheers
Stu

spaceman347
05-07-2012, 12:29 AM
Stu: The gap between the unit and the wall is approx 30cm (12") - The field service agent has been out on many occassions has hasn't commented on that so I am assuming that it's within tollerances.

There is an overhang (60cm or 2') but it's a 2 storey house so it is a long way up. Again, the feild service agent has commented that this is position well as I did query him on this.

Ross
13-07-2012, 04:08 AM
I have a few of questions?

1. Is the outdoor fan speed operation high?
2. What fan speed are you using inside?
3. Do you have zones control and if so, how many?
4. Do you have high ceiling inside (>2.4m)

On these ducted units it is important to have good airflow across the indoor unit during heating operation. If not this results in the outdoor fan slowing down or even stopping due to the High pressure rising.

Try operating the indoor fan speed on high and opening more zones. This will improve the airflow across the indoor unit and reduce the number of defrosts.

spaceman347
14-07-2012, 10:49 PM
1. Is the outdoor fan speed operation high? - Generally yes, it might slow down very occasionally but runs fast 95% of the time
2. What fan speed are you using inside? - high
3. Do you have zones control and if so, how many? - everything is on a single zone
4. Do you have high ceiling inside (>2.4m) - the lounge (30sqm of 180 total) has a 3m ceiling.

I was a little concerned about the air recycling through the outdoor unit due to the positioning based on the previous comments so i constructed an angled cowling to deflect the air away from the wall slightly. This doesn't seem to have helped at all.

martinw58
15-07-2012, 09:04 AM
is the unit sized right if undersized it will not defrost corectly

stufus
15-07-2012, 02:48 PM
I would still say the problem is with an ice bridge forming at the bottom of the coil and the subsequent defrost melt water freezing when it hits it.
Buy some heater tape and mount it in the unit base around the bottom of the coil, set it on a stat to activate @3c and see how it goes.
Most systems are gonna have trouble defrosting ~@2c and 80-90%rh
Cheers
Stu