What do you think is wrong with this unit that trips out of HP?

[paul_h]

Fuji split system, 3 phase ducted unit r410a refrigerant. AOT60umayt
Trips HP on hot days, I'm not surprised as the HP was 3650kpa.
The outdoor unit is not in the best of places, on the side of a house, 1m from the side fence that it discharges air to, 0.9m from the front fence.
So it's going to recycle some air, and it was. Ambient 33C, air on 38C.
However air off was 50C (a little high I thought even if the air on is 38c)
The liquid line was 36C, with 3650kpa on r410a equal to 59C
So subcooling is 23K, and air across the condenser was 12K
Discharge temp was 77C on a scroll, suction temp was 3C ans suction pressure was 900kpa (10c)
So I have good compressor temps, good suction temp and pressure, but high head pressure and subcooling.
It's a factory charged unit, so no-one has overcharged it.
Incondensibles in the system wouldn't give me such a low discharge and suction temp/pressure I would have though.
So why is it such a high head pressure when the liquid line before the TX only 36c?

edit: Of course the condenser was clear, the fans were working, and the indoor was working fine with a 10k split.

[ozairman]

Hi Paul,
Is the unit actually tripping the HP or coming up with abnormal discharge/compressor temp error?
also how long is the pipe run to the IU?

[nike123]

How far from wall is back of the unit and are there obstacles 1m above unit?
Also try to guide discharged air with cardboard to see if that makes any change.

[paul_h]

Nothing above the unit.
7m pipe run.
unit 160mm from the wall.
unit cut out on 0E error, which is HP error.
HP is 3600kpa, discharge is only 77C.
Actually by the time I left the unit, HP was more like 3800kpa

[nike123]

After examining refrigerant chart I saw that unit have high pressure switch. Did you establish that switch trips at rated pressure.
Also you should try to remove some charge (recover all and then add reduced amount) because unit is precharged for pipe length up to 20m. That may help in reducing pressures. I would remove 400 grams (40 grams per meter)

[nike123]

So it's going to recycle some air, and it was. Ambient 33C, air on 38C.


You obviously have problem with part of discharge air being sucked up again, and there is path to solution of problem.

[paul_h]

Yeah the recycling air is always going to happen with a unit on the narrow side of a house.
Problem is, I know many way worse than this as far as recycling air and they don't trip on HP. This one is only ambient +5C due to recycling, I've seen much worse. Also I have a feeling that the reason why recycling is even an issue to becuase the air off is too high due to system fault.
I've got no doubts that it is genuinely tripping the HP switch, not a false alarm. As I said, HP was around 3800kpa when I left, that is too high for a 33C day, or even a 38C day (which was simulated by the recycling).
Most of the time when I've seen these r410a units at similar temps (38C) they ae 3300Kpa usually, so something is wrong with the system that the pipe length and recycling air is not causing.

This thing is faulting on a 38C air on (ambient 33C, recycling causes 38C, that shouldn't be an issue because the machine should run at 38C without HP trip, that's the part I want to fix).
If it cuts out on a 42C day because recycling causes 3800Kpa ad 48C air on, then it's too bad, installation fault.
But 3800kpa HP at 38C on points to something wrong with the system.

edit: My plan was to recover, evac and recharge, then test. If pressure magically lower, I'l leave the rated amount in. If still high, I'll remove a few hundred grams.
ozairmans the expert though, and I know there's people like you nike123 that are experienced about these types of units, that's why I thought I'd put it up here and see what other people think.
But yeah I always fully intended a vac and recharge, just thought that these were an odd set of readings pressure wise compared to discharge/suction and subcool temp wise.

[frank]

It seems as though the condenser cannot reject it's heat properly (12K differential). Does the unit have an inverter driven cond fan - and if so, is it running at full speed?

Check the ambient air temp thermister against a resistance chart as this can slow the fan down if it is reading below what it should.

[paul_h]

No this is a three phase banger unit, so standard fans and they are running OK.
edit: also sensors, thermistors and PCBs changed before, though back then, then error code wasn't confirmed, and pressure wasn't so high as it was a cooler day when they checked it. I was just lucky enough to go there on a hot day :)

[ozairman]

I would be interested to see exactly how much refrigerant is in the system, whether factory charge or possibly factory overcharge or installer helping a bit, who knows. It just seems like there is too much coconut juice in the condenser with no space for it to go.
7m of pipe whilst just over the recommended does seem quite short for the average aussie ducted the FCU must be tucked right in under the eaves.

[nike123]

ozairmans the expert though, and I know there's people like you nike123 that are experienced about these types of units, that's why I thought I'd put it up here and see what other people think.
But yeah I always fully intended a vac and recharge, just thought that these were an odd set of readings pressure wise compared to discharge/suction and subcool temp wise.

You know that being near unit and sensing parts of refrigeration cycle by hand and looking at gauges and temp probes is much more descriptive than written data on paper. Nevertheless, from your readings is obvious that condenser has lot of liquid in it and evaporator is fine. Thats is why subcoling is to big and superheat is OK (you got 4-5K on TEV and 2-3k on lines). Also, you have discharge air recirculation and that combined with high subcooling gives you high head pressure. You should also take in consideration that size of outdoor unit is same as unit of 45000 btu and this also makes condenser little less efficient in rejecting heat. All that combined with fact that unit is precharged for 20 meters of lines gives you situation you experiencing.
I would start with ensuring that air don't recirculate (relocation of outdoor unit or direction of discharge air) and after that with adjusting refrigerant amount to subcooling of 7-8K because this is TEV system.

Tip: If you first going to recover and recharge, recharge with reduced amount of refrigerant and watch at subcooling. If subcooling is around 6-8k don't charge any more and wait for high ambient temperatures to see impact of your actions.

[ahamedkyana]

You check the followings again
1.High pressure switch to be sure ids working ox.
2.Check the amperage drawn by the compressor and compare with the name plate.
3.Clean the condenser.
4.If possible remove the fgreon, vacumm the system and re charge with correct amount of ***** . Be sure to use your gaige manifold and amprobe.

[setrad7791]

Quit posting stupid question's when you know the answer.....MOVE THE AC SO IT DOESN'T RECYCLE THE AIR!!! Rule number one... if the high side pressure increases then so will the low side! ie higher evap temps and lower heat rejection!

[ozairman]

Quit posting stupid question's when you know the answer.....MOVE THE AC SO IT DOESN'T RECYCLE THE AIR!!! Rule number one... if the high side pressure increases then so will the low side! ie higher evap temps and lower heat rejection!
Paul_H didn't put the unit there in the 1st place so he is not going to move it and if it is cutting out before it reaches 43°C onto the coil then something is not right, he asked for bit of help and is not an idiot.

[paul_h]

Quit posting stupid question's when you know the answer.....MOVE THE AC SO IT DOESN'T RECYCLE THE AIR!!! Rule number one... if the high side pressure increases then so will the low side! ie higher evap temps and lower heat rejection!So you're saying 3800kpa hp at 38C is normal?

I can't move the unit, I can only tell the customer to get someone else to move the unit. This is another warranty call, and if you read any of the info, even disregarding the recycling of air, there's a problem.
I'll state it simply for people like you to understand... Let's say the ambient was 38C, this unit had a HP of 3800Kpa and was tripping on HP switch, even though the condenser was clean, the fans worked at full speed, and blah blah, all the other temps I mentioned.
Can't you see that those are the things I'm interested in for now?
Do I have to self censor to stop people like you jumping on the first easy bandwagon?
I like to include all the details, but in doing so I am assuming that most people want to see the full picture.
edit: I've already said that if this was a warmer day and it was a high recycling temp, then it's an install problem, in which case my job would end.
As far as I'm concerned, I want this unit to work without HP trip at 38C air on, whether its a 38C day, or if it's a 33C day and recycling causing the 38C air on doesn't matter at the moment. Units shouldn't trip out on HP at 38C air on, Do you understand that? If so, do you understand that all the recycling is doing is causing the air on to be 38C? Also do you follow that the only reason why the air on is as high a 5K above ambient is because also something else is wrong with the unit causing high condensing temps?


edit2: I don't mean to be harsh or condescending. But if the issue was " it doesn't work a 40C ambients" and the recycling meant it was cutting out on HP because of 45C air on, I'd say move the a/c.
But the problem here is cutting out at 38C air on. That meant even if I moved the a/c so no recycling occured, it would cut out on HP whenever the ambient got to 38C or higher anyway.
So forget the recycling part, just concentrate on the 38C air on causes 3800KPa and HP trip.

[old time fridgy]

Not to conversant with Australian Fujitsu coding but are they both 10kw as you said the indoor was but in the UK a AOY54 outdoor is 14kw so if it was a mismatch system with a larger CU and smaller indoor that would cause a high head pressure and low suction. May be barking up the wrong tree but stranger things have happened. Anyway if it was not so warm their you would not have this problem, go on tell me it is winter their, have you ever seen snow?. Have a good one.

[TRASH101]

Hello Paul

I havent got the charts for 125 & 32 but it might be worth checking that incase its a bad blend. If your comp pressures/ temps are good no a reasonable day then removing some charge to 7m equivalent isnt going to hurt and is there a charge/build difference for Aus if so have you got a euro build ?