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View Full Version : Advice for newbie - please be kind..!







electricstuff
15-08-2004, 08:01 PM
I need to move the outdoor unit and extend the pipework of my Mitsu MSC/MUH series aircon (with heatpump) soon, and after getting some quotes, have decided to do it myself. Electrics etc. are no problem.

Now before all you pros shout at me, I'd like to state in my defence that I'm very good at most DIY stuff including electrics and plumbing, I've been soldering stuff for only slightly less time than I've been able to walk, can do brazing, and have never failed to put something back together after taking it apart (I LIKE taking things apart and do it a lot!). I've also spent quite a lot of time researching the refrigeration side of things. (I'm in the UK, where we don't have any of that pesky licensing stuff...)

However I'd appreciate any comments (good/bad) on my proposed method, and I also have a few queries I've failed to get definitive answers on....

Disconnection : The pump-down procedure (1) came direct from Mitsubishi.
1) Run system in cool mode for a few mins, Connect a vacuum gauge to the service port. Close liquid (small) valve, wait for zero pressure, close gas (big) valve, disconnect power. (I have an industrial vacuum gauge, but will probably buy a cheap manifold gauge set anyway - I can always Ebay it afterwards!)
2) Backfill with argon to atmospheric pressure to avoid sucking in moist air. Argon because I don't have any nitrogen and I already have welding argon (not Ar/CO2 mix).
3) Crimp the pipe closed in 2 places and cut between the crimps. Fold ends over after cutting, just to be sure. There will be a few weeks between disconnecting and reconnecting, which is why I plan to crimp the pipe ends closed to prevent moisture ingress.
I'm assuming that I shouldn't disturb the flared couplings, as I don't have a flaring tool - can you actually unscrew and reconnect flared joints without risk of leakage, or do you always need to re-flare the pipe? - it will make thinks easier if I can disconnect at the outdoor unit but I don't want to risk leaks.

Reconnection :

4) Practice brazing on some spare couplers and pipe offcuts, and saw them apart afterwards to check quality.

5) Cut the crimped ends off the pipe, and braze new pipe sections on using straight couplers, while feeding argon at slightly positive pressure through (again, argon because I don't have nitrogen)- I've seen a hint somewhere about putting a pinpricked balloon over the end to monitor and regulate flow to avoid blowing out the joint.
Assuming I still don't want to disturb the flared joints, the last 2 joins won't have gas flowing, but will still be argon filled.
6) Vacuum pipework down - I have an Edwards E2M5 pump which will pull below 0.001 millibar - I presume this is more than adequate. The Mitsu install guide says suck for 15 mins.
7) Close valve to vac pump and check for no leakage.
8) Open stopvalves slowly, then fire up system and cross fingers....

Questions I'm still unsure about....

Is there any particular type of flux I should or shouldn't use when brazing ? The stuff I've used in the past is a white powder that you make into a paste with water.

I have a high-power butane/propane blowtorch with a preheat tube - I've done light brazing with it up to half inch steel pipe (kitchen stool repair!), but it can take a while to get the work hot enough - would this do the job or do I really need something hotter like a MAPP torch ? (pipe is 1/4 and 3/8"). What shade of red does the tube need heating to for the best joint quality?

The pipe run is currently about 7m, and I need to add about 2m. The Mitsu manual says that the factory precharge is enough for up to 7m of pipe, and an extra 50g/m is needed above this - will I get away with the extra pipe length without a top-up ? It'll be about 10% light - is it that critical? I'm not too bothered about a small loss in performance, as long as there is no risk of long-term damage.

Am I correct in assuming that a 'standard set' of R/Y/B charging hoses will normally come with the right sort of connector to fit the service port ? I've seen one catalogue that lists both 1/4 and 3/8 connections - which is the right one for the Mitsu (r22) ? The outer diameter of the non-threaded end part (between the thread and the flare) of the service port is about 9mm.

Any suggestions for good sources of materials in less-than-pro quantities - pipe, couplings, manifold gauges etc.? (NE London/SE Essex) - I've found srw.co.uk, who look like they will supply things in sensible quantities online.

Thanks in advance for any advice (and I promise I'm not planning to move into the aircon business after this... I like electronics too much! )

frank
15-08-2004, 08:21 PM
Disconnection : The pump-down procedure (1) came direct from Mitsubishi.
1) Connect a vacuum gauge to the service port. Run system in cool mode for a few mins, close liquid (small) valve, wait for zero pressure, close gas (big) valve, disconnect power.

Correct proceedure


2) Backfill with argon to atmospheric pressure to avoid sucking in moist air.

No need. If you shut the suction valve at zero psig then you will not have a vacuum inside the pipe prior to opening it.


3) Crimp the pipe closed in 2 places and cut between the crimps. Fold ends over after cutting, just to be sure.

If you are going to leave the pipes open for a couple of weeks then you need to braze the ends to prevent moisture ingress.


can you actually unscrew and reconnect flared joints without risk of leakage,

You can but unless you have experience of flare joints then I would advise that you leave them alone.


5) Cut the crimped ends off the pipe, and braze new pipe sections on using straight couplers, while feeding argon at slightly positive pressure through

Purging on 1/4 and 3/8 pipe for just a couple of joints is advisable but not really necessary.


6) Vacuum pipework down - I have an Edwards E2M5 pump which will pull below 0.001 millibar - I presume this is more than adequate.

Before you start vacuuming the pipework you will need to do a pressure test for leakage. This can be done with argon but NEVER use oxygen. Pressure the pipework up to 350psig and then shut off the gauges and note the reading. Come back 30mins later and if no drop is noted then release pressure and vacuum. Run the vac pump till the suction gauge (blue one) reads -30mm then for about 30 mins. After this time shut the gauge and wait to see if any rise takes place. This will indicate moisture in the pipe - not a leak. You should wait at least 30mins.


Is there any particular type of flux I should or shouldn't use when brazing ?

Brazing copper pipes does not require a flux if you use the correct brazing rod. Ask at SRW or SWM or NRS for a cupro brazing rod. You will need at least a Mapp gas blowlamp or oxy/act kit. Plumbers blowlamps don't get hot enough.


The pipe run is currently about 7m, and I need to add about 2m. The Mitsu manual says that the factory precharge is enough for up to 7m of pipe, and an extra 50g/m is needed above this - will I get away with the extra pipe length without a top-up ?

If it's charged for 7m and you do not exceed this length then it won't require any further gas.


Am I correct in assuming that a 'standard set' of R/Y/B charging hoses will normally come with the right sort of connector to fit the service port ? I've seen one catalogue that lists both 1/4 and 3/8 connections - which is the right one for the Mitsu (r22) ?

3/8


Thanks in advance for any advice (and I promise I'm not planning to move into the aircon business after this... I like electronics too much! )

Best advice is to get a pro in to do the job. Remember you are working with high pressures. When you cut the pipe and start brazing, the heat from the torch will ignight the oil in the pipe and turn the vapours of R22 into a toxic chemical (nerve gas) - safety must be applied at all times. Do not apply heat anywhere near the service valves :eek: make your cut at least 350/400 away from the valves - more if possible. Any trapped refrigerant in a pipe will expand and burst the pipe - with devastating effect.

Peter_1
15-08-2004, 08:32 PM
Hey Electricstuff,

This is already a very good help for your and hey.... this isn't alt.hvac where they shout immediate.

electricstuff
15-08-2004, 09:08 PM
Thanks for all the info Frank, there are a few things I didn't think of in there....

For reasons I can't immediately think of, I was assuming 0psia, i.e. complete vacuum in the pipe and absolutely all the refrigirant is in the condenser. Re-reading the email from mitsu, the '0psi or below' implies they meant psig not psia!
Presumably a pipe full of refrigerant at atmospheric pressure is not a big amount to lose.

The pressure test is obvious now you mention it, interestingly the mitsu install guide doesn't mention it!
I know about pressurised oxygen and oil - I did some work with rebreathers a while ago..!

Re. the charge - it's precharged for 7m and that is what is currently there, but I need to add about 2m extra length, the question was can I get away with it being a bit light after I've extended the piping.

Thanks for the safety tip - it's in a garage so 2 big doors for good airflow. Presumably it would be a good idea to open the service valve to air when brazing the last joint, to cope with any expansion of gases in the pipe.

SRW list 'Silfos copper rod' and 'Copper to Copper Rod' - are either of these what you mean ? What is the advantage of this type over silver solder ?

I know SRW, who are SWM and NRS ?

Thanks again for your advice.

rbartlett
15-08-2004, 09:11 PM
i think this is a guy from alt hvac that already asked this question..



cheers

richard

electricstuff
15-08-2004, 09:16 PM
Yes it was.
I've now had time to think about it and research things further, and find out that I can buy any tools I need to practice the skills and do the job for way less than the figures a few people though it would cost to get someone else to do it.
And anyway, i really enjoy learning new skills...!

Peter_1
15-08-2004, 09:27 PM
Perhaps I read or I understood you wrong but NEVER, NEVER, NEVER pressurise with oxygen or there is a big chance that you will make a real bomb.
NEVER do it.

Peter_1
15-08-2004, 09:30 PM
i think this is a guy from alt hvac that already asked this question..
richard

And what answer he got there? I assume no help but shouting...as always.

electricstuff
15-08-2004, 09:32 PM
Perhaps I read or I understood you wrong but NEVER, NEVER, NEVER pressurise with oxygen or there is a big chance that you will make a real bomb.
NEVER do it.
Yes you did misunderstand - I know about this risk as I've done some work for a company that make rebreathers for fire & emergency workers (these use O2 at about 200-300 bar), and learned about all the precautions they had to take to ensure that all the fittings etc are free from oil & grease.

iceman007
23-08-2004, 12:49 AM
Just to add to everyone elses comments. Pump down procedure is correct way to do this. Shut the smaller valve off first and watch the pressure on the gauges decrease, when the pressure is reduced to maybe 1 or 2 psi shut the larger suction valve off with an allen key. All the refrigerant will be held in the condenser, and the pipes can be disconnected etc. I would braze the ends shut to keep out moisture etc.
You will need to use MAPP gas- I have one with a Sure Fire 2 torch. Heat the pipe until you get a cherry red colour and then apply the rod-use copper phosphorous ones with a lower silver content-the more silver is in the rod the easier it will flow.
Once you have reconnected put the pressure in and leave it for 24 hours if you can, and then if you want to strength test you can increase the pressure for a short time before releasing it by around 25-30 % or so.

Connect a vacuum pump-personally I would use a torr/micron gauge for the best results and vacuum down to around 200 microns. If the piperun exceeds the charge then you will need to add gas as the charge on these splits is usually critical, and if it is undercharged, you will run the risk of the indoor unit icing up, due to the low suction pressure and also the compressor relies on refrigerant for oil return. Not certain what gas you are on, as it's late and I probably didn't read the post too well, but if it's R407C or R410A YOU MUST LIQUID CHARGE ONLY it's OK to vapour charge R22. Once the extra is added open up the valves and job done.

Good Luck
James

electricstuff
04-10-2004, 12:25 PM
Well I connected it all back up this weekend, and seems to be working fine - weather's a bit colder now, but I cranked up the central heating and it put up a decent fight..!

Many thanks to everyone who provided helpful advice. The total pipe run ended up only about 0.5m over the 'need to top up' limit so not too worried about this.

Just for info, total costs were :
Tube, couplings, insulation, brazing rods, manifold gauge (SRW website) : 95 (I subsequently discovered a local branch of HRP that sells shorter rolls of tube so could maybe have saved a tenner or so)
MAPP torch (B&Q) : 23
Other oddments : bits to make coupler for vacuum pump, argon welding regulator (sacrificed due to 'adjustments' needed to get enough pressure to leak test) - maybe 20
Total about 140 - less than a third of what the original installers quoted (And I can probably get at least 30 back on the gauges on ebay..), not to mention an interesting and satisfying learning experience.

Brian_UK
04-10-2004, 06:52 PM
Hey, well done falla.

Glad to hear that all is working well and that you are still in one piece :cool: :D