View Full Version : R407 C wall mount LG 7 Kw

09-06-2004, 11:32 PM
Need an insight into this one. Last year installed an LG Wall Mount, 7Kw Cooling only R407C

In my opinion it was never as cold as I thought it should be, I put it down to the gas. never mind.........got a call today, unit is struggling

I hooked up gauges, back pressure is settled on around 2.7 Bar..........then condenser fans cut, I hear a whooshing sound as if a solonoid has opened..........back pressure zooms up to +8 Bar..........condenser fans cut back in and back pressure starts going back to 2.75 Bar again

After a while compressor and fans stop...............after a while restart again

Any ideas anyone??

10-06-2004, 02:39 PM
I am assuming this is an A/C unit?

This sounds like a defrost cycle.

Have you taken a full list of temp measurements?

10-06-2004, 02:52 PM
Hi Abe,

I agree with Gary. If it goes into defrosting cycle when its hot out, check the charge. Another problem that I would check, is the evaporator coil temp sensor. You should check its resistance to see if it is function OK. That sensor is responsible of defrost in cooling mode.

Another thing that comes to mind. Does the compressor works all the time?
You say its cooling only so there might not be a 4 way valve in the condensing unit.


10-06-2004, 03:03 PM
Given the low back pressure/low SST (about 21F), I would say the sensor is just doing it's job.

10-06-2004, 03:10 PM
Yes Gary, but if its cooling only unit then I doubt if there a 4 way valve to preform the defrost.

Faulty compressor comes to mind, the sound Abe describes is a scroll stopping and starting.


10-06-2004, 03:16 PM
A full list of temp measurements would clearly tell the story.

10-06-2004, 03:27 PM
OK, I will wait to see what Abe got to say now.


10-06-2004, 08:11 PM
Why would an A/C unit on R407C evaporating at 5C go into defrost in cooling mode?? :confused:

10-06-2004, 08:14 PM
I will take full temp readings and report back tomorrow. Yes it is AC , Cooling only.
Some time back one of my engineers opened the system, I suspect he lost gas in process
Im thinking..........do I remove all R407 and recharge again??
I know unit has fan condenser control........hence condenser fan keeps cutiing in and out
But why did the compressor cut out???

For a 8KW unit, I would have expected better performance then Im getting

Its hot like hell, wife wants me to go to supermarket........Ive been working till midnight all last three to four days.........

But, Im not complaining........

10-06-2004, 08:20 PM
Hi Frank,

I dont know how the LG is built and on our side there is no such thing as "cooling only" but......... when the evaporator coil freezes, a gefrost cycly comes in, controled by the evaporator coil temp sensor.

It can last for only a few minutes and then back to cooling.

Because Abe said its a "cooling only" unit, I figured that there is no 4 way valve and it can not go into defrost cycle.

Frome that point my thouts went to a foulty compressor.

Chemi :confused:

10-06-2004, 08:50 PM
Why would an A/C unit on R407C evaporating at 5C go into defrost in cooling mode?? :confused:

21F = -6C, not 5C. But now that I think about it, perhaps it shouldn't. We need to see the rest of the numbers.

10-06-2004, 09:06 PM
I know unit has fan condenser control........hence condenser fan keeps cutiing in and out

Have you put the gauges on the high side so you can see the points where the fans cycle off? What about amp draw? What time elapses between the comp off and then back on again?

So many questions Ayb

10-06-2004, 10:49 PM
Surely the boffins in Slough should know the answer to this ..........
Jeep XJ history (http://www.dodge-wiki.com/wiki/Jeep_XJ)

10-06-2004, 11:05 PM
I don,t know the unit you mention. But I have have worked with 407c I find it a trouble some gas (400 range Zeotropes Blends which remain in the correct proportions only as a liquid)
Its R134a R32 R125.Your pressures will be all over the place until it settlesI,ve had problems with cellar cooling where it will just not make temp then half the coil ices up then de-ices then the compressor cut out as it red hot.Its no good just topping up the system as the blend proportion will be all wrong.If it was a pre gharged unit then maybe it had a leak from manufacturer and thats why you were never happy with the temp.I would recommend leak checking and recharging but remember R407c can leak from smaller holes than ofn can.Hope this info helps


Bernard :eek:

11-06-2004, 06:00 AM
Fan speed reduces to maintain head pressure, if system is short of gas the compressor could also be cutting out on it's thermal overload.

Jasper :)

11-06-2004, 07:42 PM
Taking full readings Saturday morning............Will report soon

11-06-2004, 08:36 PM
just seen this one..;-)

it's to do with the fan speed controller adjustment.

we had this on an lg unit not too long ago. basically the fan will slow to stop. hp rises then compressor internal relief valve opens and THEN the fan speeds up.!!

check the set points on the two pots on the controller c/b or that the sensor is in the correct place...

for proof wire out and see the unit operate correctly

2.7 bar is about right but up to 3.3 would be okay (providing it's not icing back....)



11-06-2004, 08:50 PM
[QUOTE=rbartlett]just seen this one..;-)

check the set points on the two pots on the controller c/b or that the sensor is in the correct placeRichard

Im going there 2 moro..........check set points on controller c/b ??

is that in outdoor or indoor unit???

[COLOR=DarkGreen]for proof wire out and see the unit operate correctly
Please elaborate

sensor, that will be on outdoor..........where exactly should it be tied to.


11-06-2004, 09:21 PM
the circuit board is on the out door unit.
there are two dials to be set -i think the LG paper is in the car -
call me after 9.00 am tomorrow (sat)

i can talk you through it..



11-06-2004, 09:32 PM
Overfilled (?) and then high pressure bypass via the internal safety bypass and then final cut-out on the internal discharge sensor?
Just a guess.
What are discharge pressures an temperatures Aiyub

11-06-2004, 10:29 PM
Thx Rich

I appreciate your help

12-06-2004, 07:42 PM
Ok here goes..........got a bit more info.

Unit is an LG Cooling only 7.9Kw CS-C306MLBO
This is the operating scenario

Back Pressure: 39 PSI
Head Pressure, hard to tell, only can read pressure from the valve position which is after the expansion device.........no schraeders before the expansion device.
Anyway HP at that point around 75 Psi
both condenser fan and compressor ( scroll) running
then..........Condenser fan cuts off
Back Pressure starts rising slowly...........then a " whooshing" sound, which I originally thought was some solonoid opening up.........No, its actually coming from the top of compressor head........
Back Pressure rises to 110 PSI

At that point condenser fans kick back in............followed by a clicking sound, ( clicks once ) this comes from a power relay on the outdoor circuit board..........Back pressure quickly comes back down to 39 Psi

This cycle repeats two or three times.............Then both condenser fan and compressor stop running.

After around three minutes start up again.

Other data. Compressor running amps fluctaute betwwen 11 and 8 am

Outdoor Unit
Air On: 27 C
Air Off 33 C

Indoor Unit
Air On 24.4 C
Air Off 8.5 C

Outdoor Unit, Could see no pressure devices , or sensors
I suspect the condenser fan is being controlled via sensor in indoor unit.

Condenser Fan cutting in and out, making compressor hot......I think compressor is tripping out.........

Either a faulty circuit board or a faulty indoor unit sensor

Sometime back I asked Thermo Cryo for a troubleshooting , or technical manual.........They said.......we dont have such a thing

I personally feel that technical manuals are a vital necessity, LG, Do u hear?????

I bought this unit from Hawco.......

All I know, I need to get this thing sorted before real damage occurs......

Is it possible to download a manual for this particular model??

12-06-2004, 09:02 PM
Hmmmmm... Very strange. Any pressure after the metering device is low side pressure. Interestingly, 75psi corresponds to the evap air off temp. And the other low side pressure is 39psi. This suggests an EPR, designed to regulate the evap air off temp.

Also the evap airflow seems slow, but this could be deliberate, in an effort to maximize dehumidification. Another possibility could be a restriction somewhere between the two pressure reading points, acting like an EPR.

It would certainly help to have a piping and wiring diagram.

12-06-2004, 09:10 PM
What do you make of the two pressures after the metering device, Marc? Is there an EPR? Or restriction?

Karl Hofmann
13-06-2004, 02:08 AM
Just out of interest

I also have a problem with a LG 6.9Kw Casette heat pump running on R22. The problem seems to be the exact oposite to Abes problem (Air off is 1.5c, air on is 28c) the indoor coils are icing up, but what I have noticed with the condenser fan is that it will run on its slow speed for a little while, and then slow down / stop, meanwhile the compressor can be heard to become more vocal (Labouring), suddenly the fan motor fires up in its highest speed for a few mins and then return to its slowest speed, suction pressure is 55psi throuhout this. Refrigerant charge is accurate, as these units can be sensitive to the correct charge. I am of the belief that the fan control ( in the outside unit) is not as it should be, though it may also have further issues, I shall be taking a closer look at this unit next week.

13-06-2004, 02:36 PM
Without latent load, that 5C air off would eventually get you to about 30%RH. This seems like excessive dT, but perhaps the latent load is so high that you need that much dehumidification. I wouldn't want to see the air off temp any lower than that. Dehumidification sacrifices cooling power and efficiency. I would be tempted to speed up the evap fan a little for more cooling and less dehumidification.

Air off temp of 1.5C seems extremely low to me, indicating insufficient airflow through the evap coil.

Abe's air off temp (8.5C) seems about right. I think Richard nailed it. Condenser fan speed control problem.

13-06-2004, 03:15 PM
Air off temp of 1.5C seems extremely low to me, indicating insufficient airflow through the evap coil.

this isn't unusual for a UK installed japanese type split...

you must remember that these japanese systems run at much lower evap pressures -3 bar approx so on 22 that's well below freezing. this accounts for the high TD. not poor airflow

note one condenser size fits all round the world-so ours tend to be oversized for the climate...

with 'proper' fan control (99% don't have FSC fitted as std) the suction comes up to near 'normal' and therefore the TD drops back.

ask an australian what suction he normally sees from a japanese splt in summer as opposed to us working on the same kit

i guess they don't ice up that often because we tend to oversize in the UK (or at least we did in the good old days...) and therefore it has a longer off period and they are seasonal use mainly..

plus there is usually a sensor on the indoor coil to prevent freeze ups anyway.....



13-06-2004, 03:18 PM
the only fitting application for an lg wall mount is in a guard shack, hence the term "central Air conditioning", regards ;)

13-06-2004, 03:20 PM
the only fitting application for an lg wall mount is in a guard shack, hence the term "central Air conditioning",

sorry stan this doesn't mean a thing to most of us here..;-)



13-06-2004, 05:04 PM

Yes, I think it is Condenser Fan Problem..........the Indoor Unit sensor is probably faulty or not reading right

I want to connect Condenser Fan permanently in " on " position. whilst compressor operates.

This unit is only switched on during summer on hot days.

Im not sure u have wiring diagram ........please advise best way to bypass the condenser fan controller


13-06-2004, 08:39 PM

Some guys have all the luck !!!!

13-06-2004, 10:45 PM
Hi Mark

Its not a question of luck, you make your own luck in this world!! Its knowing which " key" to use for the right lock.

Sean is a very good Marketing Man, I know that. So its really great that you guys are doing some sterling and innovative work out there. ( That well hole job )

You know Reagan has just left us, well if theres anything he taught us is this, The cup is always half full.....

Getting the right type of work with the right company/ business

Anyone can put in an air con in Mr Bengalis Tandoori.......and look at his stained teeth and grin as he asks u for a discount..

Its the right clientelle......I think you guys have cracked it.......

Well Done

15-06-2004, 12:01 AM
Ok, this is an update on the troublesome LG Air Con.

I rang LG Distribution boffin with symtoms...........Guess what ??? He said wire the condenser fan direct !!!! He even sent me a wiring diagram..........Well, well........

That fan kicking in and out must have played hell with both back and high pressures......and the scroll compressor

Anyway, I put in a "fresh" charge of refrigerant......bypassed condenser fan...........and this is what I get.

Outdoor Unit

Air on 29C
Air Off 37C

Back Pressure ..........Steady on 60 Psi

Indoor Unit Air On 24 C
Air Off 7.6C

Customer says............Wow its cold in here!!!

The outdoor unit, tripped, cut off once, completely
But after that stayed on..........and ran

So we will see what happens, The LG guy says indoor unit air off must be no lower then 12C

Im getting 7.6C. Is he right?????
He said any lower then 12C and the coil will ice up.
Well on some of my units it gets to 5C and lower...

What Ive learnt.......from this

I dont think LG and R407C make good company. The way they have designed their systems dont seem to work in harmony, thats my view.

Hey Mark, fancy letting me have some of your Daikins at your preferential new prices????

15-06-2004, 04:19 AM
Evaporator airflow/dT is a trade-off between more humidity removal/longer run time/lower efficiency (lower airflow), OR more cooling/shorter run time/higher efficiency (higher airflow).

As a rough rule of thumb, in a humid area, the air off temp should be 20-25F/11-14C below the temp at the thermostat, when the room is near cut-out temp.

For example, if the thermostat is set for 75F/24C, and the room temp is 75F/24C, then the air off temp should be 50-55F/10-13C.

Heavy latent load may require a lower air off temp, but this brings us closer to freezing the coil.

In dry areas, the air off temp can be set higher (higher airflow), but too much may overload the compressor and/or condenser.

There is no "right" air off temp. Everything is balances and trade-offs, and every situation is unique. The system can and should be tuned to the particular needs of the customer.

Marc's system provides a good example of this. Because the system is undersized, the air off temp (5C) handles the latent load, but not the sensible load. I would increase the airflow a little to optimize the trade-off in the direction of a little more sensible heat removal, and a little less latent heat removal.

I would also go to full condenser airflow. This system needs all the help it can get.

15-06-2004, 08:35 PM
Indoor Unit Air On 24 C
Air Off 7.6C
As you get down to set point Ayb the air off temp will reduce and so cause frosting on the coil. The figures you give don't add up. You are only getting 8K across the outdoor unit where I would expect somewhere around 15K but you have around 16K on the indoor unit? somethings not right.

15-06-2004, 09:02 PM
As you get down to set point Ayb the air off temp will reduce and so cause frosting on the coil. The figures you give don't add up. You are only getting 8K across the outdoor unit where I would expect somewhere around 15K but you have around 16K on the indoor unit? somethings not right.

At 24C air on, it should be pretty close to setpoint.

The low condenser dT indicates more than enough airflow, which should be expected with the fan control bypassed.

15-06-2004, 10:21 PM
[QUOTE=Marc O'Brien]So now we'll never know what the problem is. My money's on "short charge", just the for the hell of it :)

I think short charge was a definate factor

I thought we couldn't read back pressure?

Could not read head pressure

On LG, low loads or low charge can cause condenser fan hunting when fan speed is controlled via sensed evaporator temperature. We don't know what fan speed control Abe's systems has, well, I don't.

The condenser fan was controlled via sensed evaporator temperature

My immediate instincts when first faced with this erratic ac was........Sensor fault, or faulty pcb, giving false readings , hence condenser fan cutting in and out, I was all out to change settings on outdoor unit pcb board...........LG guy even said, change settings , the effect i was hoping for was to allow the condenser fan to run longer

But this particular model does not have pc board on with settings which can be changed.

I posted the initial back pressure which was...........39Psi
No member pointed out that 39 Psi was probably too low and system could do with more gas and a higher back pressure..........more like 50 + Psi

Getting Condenser Fan to run was priority, and loaded with new charge, well..........something got cured..........

But, I understand what u say, I should not have had to link condenser fan direct.......System should run as designed....

Funny.........The Lg guy did not even know that the condenser fan was controlled by evaporator sensor...

I checked on progress of unit today.............Customer says it is so cold, he has switched it off!!

15-06-2004, 10:43 PM
No leak...........I pointed out my engineer opened system last year . Reason, during installation, being a cooling unit only, he thought only suction pipe required insulating.

So, he pumped down , disconnected pipes . I think in the process he " probably" lost some charge.

But the unit worked..........okayish.........after that, as I pointed out I was never entirely happy with the performance, I blamed it on R407C.........I posted a thread even about the lack lustre new gas R407C........I called it Dastardly.!!

The problem may have been compounded by the unit sitting idly all winter, and some further loss of gas.........through ill made flare.........maybe........but not significant, I dont think.

This summer.........efficiency was worse then last year........hence my probing and investigation...... Last year, CF was cutting in and out...........I did notice that.........The cassette models just run continuosly...........only the wall mounts.

But, I will carry out a through leak test.........just in case

15-06-2004, 11:11 PM
No member pointed out that 39 Psi was probably too low

Actually, I think I mentioned low SST early on, and then asked for a full list of temps.

16-06-2004, 07:54 PM
Its not just the quantity its also the blend as the glide between the gases is vast.I,m surprised the compressor has not given up.


16-06-2004, 09:50 PM
This thread just wont give up!!
Compressor is running sweet as a nut.........thanks to my swift intervention.......
And frankly..........apt and useful advice from fellow members.

My argument has been.........Yes..........R407C does glide..........but the consequences of a shortage of refrigerant.........or exessive glide conditions will cause thewhole system to malfunction........and yes.......for the compressor to fail.

Hooking fan controller to evaporator sensor is not the best design configuration.......

LG............have " screwed" up here. I am not convinced that there was a severe shortage of refrigerant........it probably needed a touch more.........yes agreed.......but on this system the gas charge has to be spot on.........

I could, if I wanted, reconnect te fan condenser through its controller, and see what happens.........

But I wouldnt want to......I know......the compressor has suffered enough.......

Would any other ac system........Mitsu, Toshiba.....Daikin.....have suffered the same fate under these circumstances??? ie: are the condenser fans controlled by evaporator placed sensors???

16-06-2004, 10:05 PM
Hi Ayb

I've been to a Daikin R407C heatpump unit that I fitted, during winter, and was amazed to see 2" (or 50mm) (another thread entirely :-) ) of ice build up on the outdoor coil (evaporator).
The outdoor fans were not running and at first I jumped to the conclusion that the unit had a problem.

Only after speakng to Daikin and understanding the operational characteristics of the software did I realise that there was no problem . The indoor room was up to temperature and the defrost logic determined that it was not time to go into defrost.

I've seen many a weird thing happen with 407 kit and still struggle to understand the logic of the software controls. Have you ever fitted a small 407 wall split, only to switch on and have to wait about 15 minutes for the suction pressures to come up to normal? :confused:

16-06-2004, 10:21 PM

I refuse to have anything to do with R407
Every 407 I have put in has had probs.................

410 A seem to be working fine though.........

Why have the manufacturers " abandoned" R407C ??????
We should get compensation from them

17-06-2004, 07:29 PM
Hi Ayb

We installed a new R407C split cassette system for one of our bigger customers about 2 years ago in Buxton. No problem with the install - worked as sweet as a nut :)

Problem came when vandals broke into the back yard one night and kicked 7 bells of sh*t out of the condensing unit and pipework :eek:

When we got there the next day we broke into the pipework and put in a nitrogen holding charge to protect the indoor unit and then tried to order up a replacement condensing unit only to be told that we could not have one as Daikin had stopped making them in readiness for the change over to R410a. We had to go back to the customer and tell him that we had to condem the whole system and install a new complete system at his cost :eek: - how embarrasing was that!

We've got the cassette in stock now for spares and we had to scrap the condensing unit.

17-06-2004, 11:34 PM
I have learnt something.............150 grams can make or break...... But in the excellence of things, one has to aspire to get things right.

So, in retrospect, perhaps, If I had paid more attention to the charge of this unit, the probs may have never occured.

But I know know how important attention to detail is.

Karl Hofmann
18-06-2004, 08:42 AM
I recently fitted a LG wall mounted unit (R407c) and spent ages trying to find the leak that I had left on the pipework. Pressure would drop and vacuum wouldnt hold no leak found, It was driving me nuts.
One of the valves holding the refrigerant in condensing unit had a slight leak and under that little extra pressure was allowing refrigerant/ nitrogen to pass HO HUM...

I shall now make a point of rcovering the refrigerant and recharging with fresh, a little overkill perhaps, but I do like things to be right

Am still to return to my little cassette, so no news there yet

26-06-2004, 02:42 PM
I spoke to a project manager of a AC maintenance company. They have had same " fractionalisation" probs with R407C

So I am not only one, only the manufacturers have kept it a " low key" affair..............No one has pointed out the major probs with R407C

No one has yet been able to tell me............" Why have the manufacturers abandoned R407C in favour of 410??"

In LG's case..............they way they designed a evap sensor to control cond fan.............is " flawed" ie: it does not make for a forgiving system.

And they wanted plumbers and electricians to installl them??????

Ha haaaaaaaaaaaaaa

I will not now fit another LG.............ever!!!! You can stick all your carrots, bonus points.........incentives

I will fit maybe Fujitsu........

26-06-2004, 03:15 PM
in my previous company there was a major issue with 407 which very very nearly ended up in court.

(the units in question came from the west country reigon..)

i think 407 will be left to wither on the vine as 410 takes hold and becomes the accepted 22 replacement as all the scare stories have pretty much died out..

these issues are all related to the speed which cfc's were driven out.



26-06-2004, 08:08 PM

You warned me about LG a year ago...............Now, I agree with you
They are the dogs dinner........Lack real class
Just shows, you can spend all the money on marketing
strut your chest.........end of the day, real quality will always prevail

26-06-2004, 08:14 PM
Hi Abe.

Just remember to keep this information away from your customers. ;)


Tony Weston
05-07-2004, 03:25 AM
G'day from New Zealand Aiyub,
I would start again, evacuate, and weigh the correct charge into the system, and then you will know you have the right amount of gas, I also think you have a faulty indoor sensor, hope this helps

05-07-2004, 10:13 PM
Hello Tony,

This " beast" is rearing its head up again, but youre absolutely right...... Just shows, The Kiwis got their heads screwed on right.

I have removed all the charge, fresh charge is in..........and the unit is working swimmingly.

But I have given the unit a head start.......I have now connected condenser fan direct, ie: it is no longer controlled by the whims of the indoor unit sensor...........( which as u say, could well be faulty)

But I am sick to my back teeth, ( assuming it is faulty, that is ) of LG stuff playing up.........when it should be new????

I have had three remote controllers pack up.........Yes three. The LCD displays play up.......

Then this beast........which I refer to as the most unforgiving air con ever built.

Why would or should you need to have a Masters Degree to comprehend the workings of an air con????

In this case.........LG dont have the foggiest how to design an air con which uses R407C

I rest my case.

Other members............may shake their heads at my impertinence.............but , me...........LG and I are not in Love no more.........we are seeking a divorce.......

And pssssssssss,, between you and I, I have a secret mistress/ girlfreind on the side !!!! ;)

Her name is..........Fuji.....and Mitsi !!!! but one blinked at me the other day.........her name is Tosh !!!!

06-07-2004, 06:22 AM
Daikin ;) ;) ;)

david mcbain
12-07-2004, 02:53 PM
can i just ask if the low ambient controll is set correctly and that you have run this unit with a probe taking evap temp if not please could you as i am interested as to what super heat you have :confused:

12-07-2004, 10:35 PM
I think u will find the readings somewhere along the thread........This unit is not fitted with Low Ambient Kit