extra length v pipe size v additional charge

[misterfixit]

Hi, i'm new to this forum (see intro forum posting), i have spent a fair time reading previous posts and will do so in the future, i am learning about domestic A/C, because split type systems are all the rage here at the moment, i have the equipment, i have mobile A/C experience (cars,trucks and earthmoving), i been reading up on various split units, the question i have come up with is due to 'additional pipe length' in reading instructions for installation on many of the cheap chinese units state that additional refrigerant is required when installed over a certain distance, ie new system is precharged (1.83kg of R22)with enough gas for a 5M back to back run of piping, the instructions become vague at that point because the installation instructions specify an additional charge of 20 grams per metre of piping, but don't take into account that the instructions cover their units from the smallest to the largest ie 1/4" & 3/8" pipe on a small unit and 3/8" & 5/8" pipe on a large unit, is there a calculation used to determine how much additional charge of R22 should be added on a per metre per diameter basis? say a large unit with 6 additional metres of piping totalling 11 meters of back to back pipe.

Also many of the cheaper units appear only to have a service port on the suction side of the system, is there normally a hidden discharge port inside the system on these cheap units? or is there an industry suction pressure which most fridgies see as being an acceptable level? (i am used to using 2 ports as a diagnosis tool for TX valves etc) The units i have looked at tend to have a maximum pressure level for suction and discharge printed on them of 1.4Mpa for suction and 4.1Mpa for discharge are these pressures well above nominal?

Any guidance you can offer is appreciated!:)

[Brian_UK]

HI and welcome.

Sounds like the Chinese have learned how to write their operating and maintenance instructions from the Japanese who, I believe translate theirs into english from the original german or something like that ;)

It's hard to say which pipe size they are referring too I suppose the best check, as always, would be to ensure that the superheat is within a reasonable range.

I'm surprised that you are able to buy R22 units still, they have been disallowed over this side for some time now. Also gas prices for R22 are climbing due to manufacturing restrictions.

You'll only find the 'hidden' service port by looking I'm afraid. It's one way of keeping the costs down, why fit another test point when your equipment is never going to need it :)

[Peter_1]

Calculate the additional content of the liquid line you've installed x density of the rerigerant and take this as the additional weight. (0.85 dm³/kg)

[NoNickName]

I would not care about the refrigerant charge in terms of weight. I would consider the superheating and add refrigerant until sensible values.

[misterfixit]

Great information and feedback thankyou, any ideas on the pressures i should be seeing? also does the head unit take the room temperature measurements to determine what cycle the unit needs to operate in? or is there a remote temp reading from the remote control etc?

[misterfixit]

Calculate the additional content of the liquid line you've installed x density of the rerigerant and take this as the additional weight. (0.85 dm³/kg)

Does this calculation sound right - i think its wrong, for all i know it could be, based on the (0.85dm3/kg)
approx volume of a 5/8 (16mm) pipe x 6 m long - 0.08dm x 0.08dm x pi 3.1416 x 60 dm = 1.206dm3

+ approx volume of 3/8 (9.5mm) pipe x 6 m long - 0.0475dm x 0.0475dm x pi 3.1416 x 60dm = 0.4252 dm3

1.206 dm3 + 0.4252 dm3 = 1.6312 dm3

1.6312 dm3 / 0.85dm3 = 1.91 kg of additional refrigerant??????????? which is of course a massive step up from the 20 grams per meter in the instructions, and is way higher than the factory charge of 1.43 kg for the unit plus the maximum 5 metres of plumbing.

for the setup i have for my first project, with the recommended additional 120 grams of refrigerant added to compensate for the extra 6 metres of plumbing, is operating and has a suction side pressure of only 2 bar (0.2 Mpa) when the compressor operating which is well below the maximum permissable by the manufacturer of 14 bar (1.4 Mpa).

any thoughts on this????:confused:


BTW. Santa is just leaving here, i hope he brings you peace and love for Christmas, merry Christmas to you all!:D

ps. I hope he brings you folk lots of gifts too!

[Peter_1]

Does this calculation sound right - i think its wrong, for all i know it could be, based on the (0.85dm3/kg)
approx volume of a 5/8 (16mm) pipe x 6 m long - 0.08dm x 0.08dm x pi 3.1416 x 60 dm = 1.206dm3

+ approx volume of 3/8 (9.5mm) pipe x 6 m long - 0.0475dm x 0.0475dm x pi 3.1416 x 60dm = 0.4252 dm3

1.206 dm3 + 0.4252 dm3 = 1.6312 dm3

1.6312 dm3 / 0.85dm3 = 1.91 kg of additional refrigerant??????????? which is of course a massive step up from the 20 grams per meter in the instructions, and is way higher than the factory charge of 1.43 kg for the unit plus the maximum 5 metres of plumbing.

Only calculate the liquid line (internal diameter of it of course because that's where the liquid is flowing) and the additional meters above factory filling you've installed.
If you have 5 m or 25 m between indoor and outdoor unit, the evaporator and the outdoor unit needs the same amount of refrigerant to work properly. The only thing that change is the longer liquid lines that must be filled with liquid and the suction line with gasseous refrigerant.
1171 kg/m³ liquid and 24.79 kg/m³ gasseous = +/-1200 kg/m³.

Or a 3/8 + 5/8 gives me +/- 60 gr/m, so factory charged for 4 to 5 m and you have 11 m or 6 x 60 = 360 gr additional charge.

Your pressures seems to be low but you need to crosscheck these with temperature readings of the SC and SH of your system.

Source http://refrigerants.dupont.com/Suva/en_US/pdf/k05736.pdf

[wolf]

man check the pressure suction line 400kpa that is all

[coolflow]

Nice to see you all wont to help, But arn,t you missing the point if this chap has been to collage and done the nessesary course he would know how to do this. this is wot i would call basic knowlage ,to re charge a ac unit as its the same as if there has been a loss of refrigerante . As i can see here a little knowlage can be dangeros and also the fact its R22:eek:

[Peter_1]

He didn't say that h's going to rechrage the system, he wants to add refrigerant to the basic filling.

Why he can't ask basic questions and who will determine if a question has to be categorised as a basic one?

[misterfixit]

Thankyou all for the help i have received, i did add the additional refrigerant that was calculated by peter, the system now has a suction pressure of 400kpa which was one of the things i was looking for in my original post, the calculation info has helped my learning in this field, to say that i should of learn t the basic knowledge in college would all depend on the teachers, some just can't teach or put more emphasis on the wrong areas, alas i have just started the course but i don't want to wait 6 months to learn the basics because every course i end up applying for seems to begin with all students being placed in the 'no know nothing basket' - courses do not tend to be structured for those wanting to step sideways within an industry.:D

[coolflow]

when you here the terms "splits are all the rage" and "cheep chines units". If my custermers had said they know wot thay are talking about then thay would not be custermers ,, more of a laugh. Then when this chap arrives at your door to fit a unit and says that he has to ask the (RE) on how to fit it, wot would you think , and Australia as well ????? . Post this on the main forum on home page and see the result. And as i have said its not hard to add refrigerante with the right knowlage ie.. amp meter .. temp gauge .. eyes

[sinewave]

Can't say I've ever used an 'amp meter' to add Refrigerant?

;)

[Peter_1]

Was thinking just the same but temp gause was OK and eyes is indeed so much forgotten.

[misterfixit]

when you here the terms "splits are all the rage" and "cheep chines units". If my custermers had said they know wot thay are talking about then thay would not be custermers ,, more of a laugh. Then when this chap arrives at your door to fit a unit and says that he has to ask the (RE) on how to fit it, wot would you think , and Australia as well ????? . Post this on the main forum on home page and see the result. And as i have said its not hard to add refrigerante with the right knowlage ie.. amp meter .. temp gauge .. eyes

Coolflow, i find your response offensive to say the least, do you also think its stupid of me to step sideways from automotive A/C and learn about 'split system A/C' installation, when uninformed people are buying cheap split type units and paying over $700 AUD (420 euro more than a weeks average wages here) to have them installed? Would you also suggest that my learning projects all be top quality units which are 3 times the purchase price? You find it easy to knock the popular 'cheap Chinese units', yet in your posts you ask for help for a brand of unit for which nearly 7,500 members have never posted about before? Is it my responsibility to make a decision on what a customer buys at the store? because if it is, i have a lot of territory to cover and if you even think that i would complete an install for a paying customer before completing my training you are sadly mistaken.:mad:

By the way, as a fully qualified cert3 Automotive Electrician of 24 years experience and a cert4 qualified 'workplace assessment and training' practitioner (i could write myself the A/C ticket/qualification but i am undertaking a course anyway) , i have never ever had the opportunity to see or use an 'amp meter', the device for measuring electrical current is correctly called an 'AMMETER' :rolleyes:

[Peter_1]

..., i have never ever had the opportunity to see or use an 'amp meter', the device for measuring electrical current is correctly called an 'AMMETER' :rolleyes:


This is what I call an offensive post for all the non-English speaking posters here, including myself.
Try it once in French, German or better in Dutch my friend... then we all can put a very big :D after your post :mad:

[coolflow]

Hi to you all.If you mean the Diatsu or Hiyasu then(look and thou shall see) that thay are made by General/fujitsu.!!!! Then you go on about the amp meter , you obviosley knew wot i was talking about.???? .
When you put your AMMETER on the feed to the comp and see its amps match the data on the plate then this would second the confidence that you have the right charge in the ac unit.And as for quoting your qualifacations that is just sad.this will be the last post i put on this subject so you are the weakest link GOODBYE.

[Peter_1]

The brand and/or athe attached nameplate with technical numbers on the machine has nothing to do with the proper charging method.

I can give you more than one situation where the AMPS will be correct but with a faulty charge (restricted circruit, dirty condensor, compressor wear, fanspeed not correct, dischargin too high,...)

Adiós

[coolflow]

I said i wouldnt but i thourght these were bnib units.:cool: