fujitsu ao*30RLA

[paul_h]

I haven't worked on a fuji ducted for ages.
This is an old one for me, I replaced the compressor 2 years ago in summer.
Anyway, I'm called back again in winter 2 years later, they say airflow is bad now certain areas not heating (but worked fine last winter after I was last there).

I check everything, it all seems fine, filter a bit blocked, as well as that, it is a small unit not big enough for a whole house. Unfortunately the installers put two switches in for zone control, 1 for bedrooms, one for living areas, instead of a single day/night switch, so they tend to try run both zones.

But a closer look at how the system is running shows a few things not quite normal.
They had the system set to fan high, HEAT, and 30C setpoint, and run it all day.
So it had been running flat out for a few hours when I got there in the afternoon, ambient 16C, inside temp 20C at the return (common area between the living and bedrooms).

I noticed the outdoor fan spending most of it's time cycled off, so air out of the indoor was only 34C.
Suction service valve was 85C which seemed high to me and probably why the indoor coil sensor was hot and cycling the outdoor fan off.
With the outdoor fan on, HP went up to 2200kPa, LP was 360kPa, liquid line return was 31C.
With the outdoor fan off, HP down to 1700kPa, LP down to 200Kpa, SSV 79C, liquid line 29C.

So to me temps and pressures high, differential across the indoor low, and I've never seen one of these have the outdoor fan cycle off so much when the indoor return only 20C.

But first question is anyone know what size return air duct these should have?
It's got a single run of 400 diam flex 6m long, off a 350mm x 900mm filter.
I just want to make sure it's getting enough air before I start scratching my head about the temps and pressure.

[nike123]

Paul, just remove flex duct from indoor unit intake and see if that action changes behavior significantly.
Do you have hot wire or small vane anemometer?
http://www.testo.com/online/abaxx-?$part=PORTAL.INT.ProductCategoryDesk&$event=show-from-menu&categoryid=25122804

I think that outdoor unit fan should cycle between low and high speed and not to ON-OFF. Maybe outdoor fan is faulty or thermostat in outdoor unit is faulty.
If your airflow is OK than unit achieves only 7,8 kW.
If unit is working OK than your air off temperature should be 37°C (for 20°C intake) or higher if filter is clogged or air flow is inadequate.

I would start with recovery and weighing of recovered refrigerant.

http://www.uel.ru/downloads/Fj-ary30ala_rla-sm.pdf

[ozairman]

As you know Indoor pipe temperature is the key to the control of the unit on heating. Heating overload protection will come in to operation somewhere around the low to mid 50°C coil temp. Heating overload stops the outdoor fan dead, the only time it will drop to low speed on heating is based on outdoor ambient temp but I can't remember the exact number at the moment (over 20°C I think)

Your 2200kPa HP equates to about 56°C so spot on with HOLP occurring but 32°C on the liquid line indicates a lot of subcooling occurring in the indoor unit? So is airflow higher rather than lower, or is the indoor coil full of liquid? how did you charge it last time you replaced the comp? Did you note what the compressor amps were?

I know you went to the same college as me so you should be able to work out if the R/A duct and filter is the correct size but this should jog your memory ;)
Airflow at 100pa is about 450ls, so a 400mmØ flex (0.125m² area) will give you about 3.6m/s velocity which is fine for a flex duct R/A.
A 350 x 900 R/A grille will give you about 1.6m/s face velocity working on 90% free area, again fine for the standard aussie flat frame filter.