how to calculate extra refrigerant

[back2space]

My installer is coming back out to add more refrigerant as the unit isnt performing great in heating.

LG have advised to weigh it in and use this formula:

http://mylg.co.uk/data%20for%20site/Multi%20Splits%20commissioning.pdf

and use the FM24 Calculation,

The installer however says he isnt going to do this and has a better way of doing it.

He says he will put the units into max cooling...

Then he will add refrigerant until his guages read 0 and says this way you will get the exact ammount???

Is this the right way, hes coming in half an hour to top it up can any one advise me.

[monkey spanners]

He will need to be taking all the refrigerant out to pressure test with ofn to check for leaks before adding refrigerant, so why not then weigh it back in. All leaks need fixing first! If it is short is has gone somewhere!

Top ups are for mobile phones not ac or refrigerating systems....

[aircon50]

Are you sure your installer knows what he's doing? Or.. is he just an 'installer'? I wouldn't even let him (or her) get near it, yet alone put gauges on! I fail to see how adding refrigerant (presume R410a) until gauges read 0 makes sense. Normal split, non-inverter, R410a, will run somewhere in the order of 7 to 8 bar. (That's in excess of 100psi (gauge))
The LG method is the correct method!

[back2space]

He will need to be taking all the refrigerant out to pressure test with ofn to check for leaks before adding refrigerant, so why not then weigh it back in. All leaks need fixing first! If it is short is has gone somewhere!

Top ups are for mobile phones not ac or refrigerating systems....

There isnt a leak on the system but because the new pipe run is 24metres this exceeds the pre charge length so additional charge is to be added.

It worked fine before but this didnt exceed the pre charge length so didnt need additional charge.

He is a proper company but I think hes wanting to do it the quick way, I dont want any problems with it.

Last week was milder and the system was heating fine, its colder this week and the system is struggling if 2 units are on depsite this not exceedign the capacity of the outdoor unit, this only happens if all 3 indoors are on at the same time requesting heat.

The air off temps are about 31C on thermostat on at present even if set to 30C on the remote control if 2 units are on.

It only starts to chuck out higher air off temp when their is only one unit pysically switched on which again confirms that their isnt enough charge in the system!

How long will it take him to recover the refrigerant and sort this out so I know as a guide.

The total pipe run is approx 42metres.

[monkey spanners]

If the unit still has the correct factory charge in it (which it won't as one atmospheres worth of the refrigerant will have been left in the pipe work when stuff was moved) then you can just add the correct grams per meter to bring it up to the correct charge.

Personally i always end up overcharging stuff when trying to do things by gauges so i'd weigh it in. Each to their own :)

[back2space]

No equipment has been moved at all.

The existing units have been untouched.

All thats been added is another indoor unit which has its own separate pipework running back to its own port on the outdoor unit.

Ive told him hes to weigh it in but as he has done the job at cost price (made no profit on the indoor unit due to me buying this separatly) he doesnt want to recover the refrigerant thats already in and says he will calculate how much to add based on LG formula.

He says will cost him if he has to remove the gas as he has to get the cyclinder etc cleaned out.

LG originally told him that the unit didnt need additional charge as he rang them.

[monkey spanners]

In that case the extra grams per meter is what i'd do. Its difficult to give a valid opinion when you don't know all the history.

[cadillackid]

the more I work on minisplit systems the more I find in my test lab and in the field that the ONLY way to charge them is by weight... and most manufacturers have a chart in the istall / service manual that tells you the formula for calculating additional refrigerant needed for expanded pipe lengths.. it will vary depending on the pipe sizes....

it is also in colder weather going to be somewhat normal to see lower duct temperatures when multiple units are calling versus just one indoor unit calling.. as when one unit calls you have the whole condensor area outside (designed for 3 units) to move the heat required by one indoor unit...

heat pumps do exactly as the name implies.. they move heat from outside to inside during heat mode..

you installer tech should do the following:

1] read the manual and find out what the pre-charged pipe-length was that the unit was shipped with,

2] measure or find out from original install documents how much piping was actually used on system...

3] if the piping is greater than factory design... use formulas and add appropriate refrigerant and check system operations...

if you REALLY want to do it right... recover the complete charge and weight it... check it against the design spec.. if you weigh-in a lot less than the original pre-charge suspect a leak...

-Christopher

[back2space]

Ok hes coming out to weigh in the refrigerant.

HEs worked out need 330grams extra into the unit.

Just a question: If the unit is overcharged slightly for example if the he worked out the piperun was 39 and it should have been 35 would this cause a malfunction with just those 3 metres?

[rude]

Probably not, also make sure he charges it with liquid.

[back2space]

What a joke this is,

Air con air off temps are worse than ever now, turns out hes added way too much refrigerant and should have only added about 130g.

Need someoen to come out and recover the refrigerant and weigh it back in properly but dont wanna get same guy out again as he is just messing about everytime I correct him and tell him how he should be doing it.

Why is there no one reputable in Leeds. :(

[rude]

Ha its like one of the easiest jobs to do.

[eggs]

Why is there no one reputable in Leeds. :(

There is, I know of a few.

The trouble is that reputable companies charge reputable company prices and people who want jobs doing for pocket money cash, do not want to pay reputable company prices.

The words "Peanuts" and "Monkeys" spring to mind.

If you want that LG of yours sorting out once and for all, you really need to get a reputable company in.....and for heavens sake don't stand over the engineers shoulder telling him how to do his job.

Eggs

[back2space]

Yeh but the fact that I havent been watching him do the work means I am in this situation now. Its only after has this happened.

Got someone coming tmrw to evacuate and weigh the gas back in.

Should cost about £80 he said depending on how long it will take.

Thanks.

[Thermatech]

Part of the issue here is that the LG unit is using latest R410a refrigerant but still using old R22 refrigerant circuit & suction accumulator technology.
The unit is only pre charged for 7m of interconnect pipe & only has very small tiny suction accumulator to keep manufacturing cost low. So there is very little if any flexibility in refrigerant charge.
+ or - 100 or 200 grams & there is a big difference in performance.

This LG system looks more like the old R22 Mitsubishi MXZ from about 10 years ago but with lots of stuff removed to make cheaper & with R410a refrigerant.

If you look at the old R22 Mitsubishi MXZ which is a similar product you will see it has two very large suction accumulators which allowed for long precharge interconnect pipe length.
If you look at the latest R410a MXZ system you will see it has suction accumulator & liquid line 'power reciver'. This system is optamized for R410a as can be seen from the new design. It is pre charged for 40m of interconnect pipe.
So for this application there would be no requirment for any additional charge with the MXZ system.

As this case shows its very easy to overcharge the LG system.
But what safety fuction has it got to protect against refrigerant overcharge ? Will it continue to run with liquid flood back untill the compressor stops on overcurrent ?

On the MXZ system the outdoor unit constantly monitors compressor hz & discharge temp. Under some conditions if the discharge temp gets too low the unit considers that the refrigerant is overcharged & stops on a fault before liquid flood back to compressor. So it will protect against overcharge.

Did the LG design engineers include this safety function or did they leave it out to make the unit cheaper ?

[back2space]

Part of the issue here is that the LG unit is using latest R410a refrigerant but still using old R22 refrigerant circuit & suction accumulator technology.
The unit is only pre charged for 7m of interconnect pipe & only has very small tiny suction accumulator to keep manufacturing cost low. So there is very little if any flexibility in refrigerant charge.
+ or - 100 or 200 grams & there is a big difference in performance.

This LG system looks more like the old R22 Mitsubishi MXZ from about 10 years ago but with lots of stuff removed to make cheaper & with R410a refrigerant.

If you look at the old R22 Mitsubishi MXZ which is a similar product you will see it has two very large suction accumulators which allowed for long precharge interconnect pipe length.
If you look at the latest R410a MXZ system you will see it has suction accumulator & liquid line 'power reciver'. This system is optamized for R410a as can be seen from the new design. It is pre charged for 40m of interconnect pipe.
So for this application there would be no requirment for any additional charge with the MXZ system.

As this case shows its very easy to overcharge the LG system.
But what safety fuction has it got to protect against refrigerant overcharge ? Will it continue to run with liquid flood back untill the compressor stops on overcurrent ?

On the MXZ system the outdoor unit constantly monitors compressor hz & discharge temp. Under some conditions if the discharge temp gets too low the unit considers that the refrigerant is overcharged & stops on a fault before liquid flood back to compressor. So it will protect against overcharge.

Did the LG design engineers include this safety function or did they leave it out to make the unit cheaper ?

HI Thermatech

According to the LG data book for my unit it states it has low pressure switch but high pressure switch not fitted.

Why would the fan be running fast in cooling mode and outdoor temp of 5C whereas before it was running slow even in ambients of 25 plus.

[Thermatech]

A low pressure switch will not protect the system from refrigerant overcharge.

For cooling low ambient control I have no information about the LG control stratagy as nothing in the service manual but you might find that the LG unit only has 3 speed outdoor fan off / low / high with a fan motor with two windings one for low speed & one for high speed & you might find that it only operates by outdoor air temp.

So its difficult to know exactly what the fan should be doing unless LG publish the full control stratagy.

BTW
The MXZ has 3ph dc fan motor with full electronic veriable fan speed stratagy based on liquid line pipe temp.

[back2space]

A low pressure switch will not protect the system from refrigerant overcharge.

For cooling low ambient control I have no information about the LG control stratagy as nothing in the service manual but you might find that the LG unit only has 3 speed outdoor fan off / low / high with a fan motor with two windings one for low speed & one for high speed & you might find that it only operates by outdoor air temp.

So its difficult to know exactly what the fan should be doing unless LG publish the full control stratagy.

BTW
The MXZ has 3ph dc fan motor with full electronic veriable fan speed stratagy based on liquid line pipe temp.


The condenser fan has many different speeds as it is a BLDC motor, I have seen it rotating at many different speeds dependant on the load.

There aint actually that bad to be fair on them, I guess the equipment will not perform if its not been installed properly.

BUt yeh I agree there is no HIgh Pressure cut out, only to protect of low pressure.

[back2space]

UPDATE:

The unit had a leak, at 2 of the flare nuts from the originally installed units from 2yrs ago.

The system was running with about 460g of refrigerant when it should have had in 2330g but was working fine in cooling!!

The guy who came out was great, did everything the right way.

Im so annoyed with the guy who fitted the 3rd unit, whilst his pipework was neat and no leaks from that his poor skills and refusing to weigh out the refrigerant properly by removing it all then weighing back in has meant that yes he added 640g to the measly 460g that it had left in it but did not detect the leaks etc and kept saying the system was performing well when clearly to anyone in the know who has any sense about them I knew it was not!

Unit now ramping up nicely and running at nice air offs and achieving nice hot temperatures... At least!

and I shall now breath and can relax knowing that I have found someone decent to service my units and who deserves more business due to doing things the right way.

Charged me £130 to sort out that was all work in and he was here from about 10am only just left at 2.

[cadillackid]

the protection of high pressure on these units is handled by measuring pipe temperatures on either coil... in heat mode the indoor pipe temperature measurement is used and in cooling mode the outdoor pipe temperature... so really there is no need for a high pressure switch... for low pressure they cannot use pipe temperature so they often have a sensor in thyese units for that...

these things will also run a very low charge in cooling but fail to properly heat... the expansion device is in the outdoor unit so much more refirgerant is required to heat since the high side of the system is the COMPLETE pipe system in heat mode..\

whereas in cooling mode the high side of the system is contained outside.. so it requires less refrigerant to get good condensation in the condensor... the complete pipe length is on the low pressure side... refrigerant will already be evaporating in the ""Liquid"" line going into the building

since the computer in these units protects from coil freeze-ups indoors you wont see ice if its low on charge...

in heat mode freezing across the expansion device on outdoor units is controlled by the system lowering power to avoid defrost cycles.. esp if it is close to or slightly above freezing outside.. what you get inside as a result is very low heating capacity from both the low refrigerant and also the computer defrost avoidance,...
-Christopher

[paddyaircon]

130 quid is cheap for 4hrs and gas ofn and bits etc

[back2space]

Looks like the same issues im having now... looking back we had poor heating performance last time.

What I dont understand is when more than one indoor unit is running good air offs are experienced but isnt there trhe same ammount of refrigerant in the system or is it because the compressor is ramped up its not affected as much by low refrigerant.

This is affecting the 2 furthest units. Pipe length I have is 8 metres followed by 10 metres followed by final unit of 23metres.