Hitatchi Vrf defrost problem

[marc5180]

I have to go to a site tomorrow where they have a Hitatchi RAS10FS that was supposedly like a block of ice. I managed to get a guy on site to manually push in the defost button on the outdoor board which cleared most of the ice.

My first question is; when does the deforst cycle normally happen is it when the condensor coil temperature reaches say -10C and if it is then is it normally the same for most brands i.e daikin, mitsi and how long does it normally last? Does it defrost for a set time or defrosts until the sensor is satisfied.

Secondly i have been told that the outdoor fans weren't running after the system had been manually defrosted, i thought the outdoor fans should run when the indoors are on heating or is it because the indoor supply air is quite high and so it switches off the outdoor fans to bring the temp down.

Sorry for all the questions...again:)

[superswill]

the outdoor fans not running maybe a clue but in this cold we are having they may just be held of by the PCB/HP control at the point when checked,i had this yesterday (iced up soild) on a VRF and found it 7kg sort of gas so maybe worth a look

on defrost found this in my inbox,from daikin,intresting read

In 2008 Daikin VRVIII Heat Recovery system won "Product of the Year" atthe prestigious HV Awards. One of the major factors in achieving thisaccolade was the ability to provide continuous heating during defrost andoil return cycles. The standard VRF system provides no heating capacityduring the defrost cycle. Effectively, the VRF system switches to acooling cycle where the indoor coil temperatures can drop to -20°C. Atthis point the indoor unit shuts off completely, depriving heat to theoccupied space for up to 18 minutes in any given 90 minute period. Withthe Daikin VRVIII Heat Recovery system, the indoor coil temperatures neverfall below +25°C during defrost or oil return, thereby continuing theheating process while avoiding the transmission of cold draughts into theoccupied space. So When Does Defrost Occur?Loss of heating during the Defrost Cycle has proven over many years to beone of the most problematic situations associated with VRF / VRV systems. It is a common misconception that the defrost cycle only occurs duringinitial heat up, or during periods of extreme cold. In fact, when theambient temperature is below 0°C, there can be little moisture in the air,thus rendering ice build up on the outdoor coil unlikely. Defrost is muchmore likely to occur where the ambient temperature is between 2 - 10°C. With the unpredictable British climate, a defrost cycle may be required atany time, day or night, during the late autumn, winter and early springmonths

[Thermatech]

For Set Free standard defrost operation on latest R410a units.

1/ 40 minutes heating operation then defrost available depending on the following start conditions

2/ temp diff outdoor air & evaporating temp at outdoor heat exchanger = large temp diff

3/ Defrost

4/ Discharge pressure above 17 bar & evap temp above 15 deg C

5/ Defrost completetion

6/ Max defrost time 10 minutes

The defrost start condition depends on the outside air temp
At any outside air temp above 6 deg C defrost will start at -4 evap temp.
At outside air temp 0 defrost will start at -8.7 deg C evap
At outside air temp -5 deg C defrost will start at -12 deg C evap.

There is an option for defrost start condition which can be set at the outdoor control circuit board which changes the start conditions but for UK the factory setting is most likely the best setting.

The good thing with Set Free systems is that you can monitor all the operating data for the complete system at the outdoor unit circuit board so its easy to see the operating temperatures & pressure to check that the circuit board is getting correct data from the sensors.
But you do need the service manual.

[marc5180]

the outdoor fans not running maybe a clue but in this cold we are having they may just be held of by the PCB/HP control at the point when checked,i had this yesterday (iced up soild) on a VRF and found it 7kg sort of gas so maybe worth a look

on defrost found this in my inbox,from daikin,intresting read

In 2008 Daikin VRVIII Heat Recovery system won "Product of the Year" atthe prestigious HV Awards. One of the major factors in achieving thisaccolade was the ability to provide continuous heating during defrost andoil return cycles. The standard VRF system provides no heating capacityduring the defrost cycle. Effectively, the VRF system switches to acooling cycle where the indoor coil temperatures can drop to -20°C. Atthis point the indoor unit shuts off completely, depriving heat to theoccupied space for up to 18 minutes in any given 90 minute period. Withthe Daikin VRVIII Heat Recovery system, the indoor coil temperatures neverfall below +25°C during defrost or oil return, thereby continuing theheating process while avoiding the transmission of cold draughts into theoccupied space. So When Does Defrost Occur?Loss of heating during the Defrost Cycle has proven over many years to beone of the most problematic situations associated with VRF / VRV systems. It is a common misconception that the defrost cycle only occurs duringinitial heat up, or during periods of extreme cold. In fact, when theambient temperature is below 0°C, there can be little moisture in the air,thus rendering ice build up on the outdoor coil unlikely. Defrost is muchmore likely to occur where the ambient temperature is between 2 - 10°C. With the unpredictable British climate, a defrost cycle may be required atany time, day or night, during the late autumn, winter and early springmonths

Thanks for that Superswill, interesting read.
I got over to the system today ran it up and found pressures and temperatures pretty low. Rather than just "top it up" i thought it would be better to remove the charge to see if any had been lost but it hadn't. I recharged it but only got it up and running late afternoon
I left it for an hour to go through its preliminary checks then went back to it and found it running well, pressures and temps all seemed ok but it didn't go on defrost and it didn't ice up.
Outdoor condensor fans were running as well. I needed to get more details of how the defrost cycle works before i can fault find it- i tried ringing technical but have been told they have closed that department:mad:

[marc5180]

The defrost start condition depends on the outside air temp
At any outside air temp above 6 deg C defrost will start at -4 evap temp.
At outside air temp 0 defrost will start at -8.7 deg C evap
At outside air temp -5 deg C defrost will start at -12 deg C evap.

There is an option for defrost start condition which can be set at the outdoor control circuit board which changes the start conditions but for UK the factory setting is most likely the best setting.

The good thing with Set Free systems is that you can monitor all the operating data for the complete system at the outdoor unit circuit board so its easy to see the operating temperatures & pressure to check that the circuit board is getting correct data from the sensors.
But you do need the service manual.

That makes sense thanks,
I spoke to somone today that used to work for hitatchi who told me that i could check the operating data from the outdoor PCB on PSW2 but without knowing what the settings stand for then im just guessing. In the manual that i have it doesn't mention these settings so i dont know how to find them out.

I wanted to try and read what the heat exchanger coil was reading and from what you have said above i should also have been looking for what the outdoor air temp sensor was reading which should have told me if my problem was a sensor or even the board.

[Thermatech]

Same deal with Hitachi

Register
get password
down load manuals

[marc5180]

I couldn't find the right manual, but i have it now and it does show what all the codes mean so i'm made up.
I'll print this off as well and keep it in my van.
Cheers Guys

[Thermatech]

Thats the only trouble with manuals
you end up with 100's of them.

I have one box of manuals for each manufacturer.
If I am going to a site visit with Hitachi system then only the Hitachi box of manuals gets put in the car.

But then I also have all the manufactures manuals on the lap top as a back up.
I cant remember everything but I know where I can find the info.

[marc5180]

Surely you dont have to have a manual for every single make and model out there do you? Can you not make a custom one for each manufacture like you described before?

[Thermatech]

The thing is you dont always get the best advice from the lads on technical help desk.
Thats not a critisism of all technical help desk staff.
But really its not a very pleasant job.
If you were to try & do it even for one day you would know what I mean.

There is no way I would sit behind a desk all day & answer the phone.

The pay for that job possition is not the best so there is alot of churn & enginners quikly get fed up with it & move on.

But

If you have the service manuals you should 99% of the time be able carry out any trouble shooting without the need to ring technical help desk.

My site visit for today was a classic example.

VRF system poor heating performance & tripping on faults.
Contractor had been to site many times but could not resolve so called in assistance.
Low pressure sensor reading 5 bar lower than true value.
We found the problem within 10 mins of taking the panel off the outdoor unit.

But the engineer did not have any manual & so did not know how to trouble shoot pressure sensor faults.

So now he does & next time he will know what to do.
But he was a bright lad & Im sure he could have worked it out himself if he had the service manual.

We all need to use technical help desk sometimes that why manufactures provide the service & some of the enginners who man the THD do a really good job & know there stuff.
But if lots of enginners are ringing up all the time for silly little things that they could resolve themselves if they had the service manuals then those engineers who really need the THD instead of waiting in a que for ages could get prompt service.

[marc5180]

Too be honest, i didn't know that the manuals would provide me with in depth troubleshooting but now i know and i've started downloading a fair few of them onto my laptop so i can look when on site.