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! )
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! )