HVAC-Talk: Heating, Air & Refrigeration Discussion banner
Cancel
Create thread New Forums

Connecting 3/4 line into 7/8 coil fitting - what's the best way?

1 reading
Jump to Latest
1 - 20 of 49 Posts
G

garya505

· Registered
Joined
·
2,506 Posts
Discussion starter · #1 ·
This is another detail that I didn't want to know, but I'm getting contradicting contractor "opinions" on this one. The lineset specified for my condenser is 3/4 and 3/8. The 3/4 line has to go into a 7/8 fitting on the coil. Of course the contractors don't agree, but each one states their opinion as fact. So, now I have to get to the truth on this one.

Here's what I have been told:
- One guy says he has to use a 7/8 line so the fittings will match.
- One says he always uses a reducing coupling or a reducing bushing (he says this is the only proper way).
- One says he can expand the end of the 3/4 line to fit the inside of the 7/8 coupling.

My thoughts:
I think using a bigger line is silly. Expanding the end of the line doesn't seem like great idea. For a coupling, it seems like on a the 3/4 side of the coupling it would have a smaller ID, creating a slight restriction at that point (or maybe I don't understand how a "reducing coupling" works). Would this affect performance? Seems like a "reducing bushing" would be best then, but I want to know what the experts say.

What's the truth here? What is the best way, and what other ways would be acceptable?
 
#2 ·
Swedge the line-set, one joint to solder.

But that's just my opinion.
 
Save
Like Like
#3 ·
Makes no sense to use a larger lineset. Makes no sense to enlarge the 3/4 pipe. They make these things called reducing couplings or a reducing bushing. I prefer the bushing. It's a 3/4 coupling X 7/8 bushing. Very clean and simple, two joints and it's done. :.02:
 
#4 ·
Option 2 or 3 will work just fine. But option 3 means only one joint, less likely to leak, and less heat on that service valve.
For the guy who "must have" 7/8 line... ask him what he does when the coil at the other end requires 3/4 inch?
If 3/4" is specified, that's all you need... unless your line is much longer than what's stated in the instructions. Then you will need to increase at least part of the line to 7/8... again, ask the guy what he does in this situation. Sooner or later, you have to use either a reducer or an expander.
 
#5 ·
As long as the tech purges dry nitro through the lines while brazing and does a proper job of brazing all joints, it's more a matter of what he has on the job and what he's most comfortable doing. If a reducing coupler is his cup of tea, great. If he prefers to swedge (expand) and make one joint, fine. As for having a larger line throughout, I'd vote against that as it could be detrimental to the system and/or capacity issues. It's never a good idea to do field experiments, IMO.
 
Save
Like Like
Discussion starter · #7 ·
This is interesting.

I realize now that using a 7/8 line requires a fitting at the condenser end so that's bot just silly, it's plain dumb.

Other than that, I would have expected that swedging (expanding) would have been the last choice, but that appears not to be the case.
 
Discussion starter · #8 ·
OK, so here's what I'm getting from all of your input so far. Using a reducing coupler, reducing bushing, or swaging all appear to be acceptable methods. The swaging method has the advantage of only one solder joint. Some think that the coupler or bushing is a better method than swaging, but I haven't seen anyone state a reason for that, yet.

Doing a little digging, I see that Mueller Industires makes both reducing coupling and a bushing for 7/8 x 3/4, so either of those methods can be done with an off-the-shelf part. For swaging, no parts are required but I suppose the tools and skill of the guy doing the swaging would be factors in the quality of the joint.
 
#9 ·
garya505 said:
For swaging, no parts are required but I suppose the tools and skill of the guy doing the swaging would be factors in the quality of the joint.
Click to expand...
I swage copper to also cut down on leak possibilities, but the cons from what I have heard, is the copper looses some of it's integrity if you swage it, I don't know I guess the jury's still out on this.
 
Save
Like Like
#10 ·
Only real downside to swedging is the operator and equipment, some can over expand the pipe and thus creating a sloppy fit or under expand creating a tight fit with poor braze flow.. The other side is that when you expand you thin the material.. negligible amounts I would guess. I would go with the coupling reducer simply for the ease of insuring proper heat transfer and flow of braze.

But thats just my $.02
 
Save
Like Like
Discussion starter · #11 ·
Mr Bill said:
I swage copper to also cut down on leak possibilities, but the cons from what I have heard, is the copper looses some of it's integrity if you swage it, I don't know I guess the jury's still out on this.
Click to expand...
That's what I was wondering about. Seems like swaging (stretching) a 3/4 O.D. copper line to 7/8 (0.875) O.D. must thin the copper significantly. This is more of a stretch than just for coupling two 3/4 lines, which I'm sure is done all the time, but for that the line only needs to be stretched to 0.750 I.D. (about 0.792 0.D.). Swaging a 3/4 O.D line to fit a 7/8 I.D coupler on a coil requires about three times as much stretch as the swage for joining two 3/4 lines. I'm assuming the tubing wall thickness is 0.042, but I think some 3/4 lines might have 0.035 walls.

Rcb2875 said:
Only real downside to swedging is the operator and equipment, some can over expand the pipe and thus creating a sloppy fit or under expand creating a tight fit with poor braze flow.. The other side is that when you expand you thin the material.. negligible amounts I would guess. I would go with the coupling reducer simply for the ease of insuring proper heat transfer and flow of braze.

But thats just my $.02
Click to expand...
Ah yes, the skill of the person doing the swage, that would be important. For the reducing coupler or bushing, you just gotta be good at brazing.
 
#12 ·
garya505 said:
That's what I was wondering about. Seems like swaging (stretching) a 3/4 O.D. copper line to 7/8 (0.875) O.D. must thin the copper significantly. This is more of a stretch than just for coupling two 3/4 lines, which I'm sure is done all the time, but for that the line only needs to be stretched to 0.750 I.D. (about 0.792 0.D.). Swaging a 3/4 O.D line to fit a 7/8 I.D coupler on a coil requires about three times as much stretch as the swage for joining two 3/4 lines. I'm assuming the tubing wall thickness is 0.042, but I think some 3/4 lines might have 0.035 walls.



Ah yes, the skill of the person doing the swage, that would be important. For the reducing coupler or bushing, you just gotta be good at brazing.
Click to expand...
I wouldnt say that it thins it "significantly" by any means. And honestly if you knew what the thickness of the copper tubing in your evaporator and condenser coil was, you may be suprised.
 
Discussion starter · #14 ·
heaterman said:
To reduce the risk of damage to the expanded (swagged) copper resulting in a poor fit or leak, we use reducing bushings.
Click to expand...
I'm starting to think that a reducing bushing might be the best solution in this case. The lines will have to come out horizontally 8" from the coil to clear a humdifier bypass duct, then turn straight up vertically for 5 feet to the ceiling and 2 feet throught the flat roof. It can be supported at the ceiling penetration, but the 5 feet is still vulnerable to being bumped I guess. So, a stronger connection, with no swage fitting problems or thinning of the tubing, might be a good thing in this situation.
 
#15 ·
aintitfun said:
I wouldnt say that it thins it "significantly" by any means. And honestly if you knew what the thickness of the copper tubing in your evaporator and condenser coil was, you may be suprised.
Click to expand...
I believe the risk of a bad swage doesn't exist in the material holding the pressure, but lies with the line having to bear outside stress from say, someone having to adjust the unit or someone bumps or pulls on the line, etc. Also depends if bump or pull on the pipe will cause to pipe to twist or bend at the joint. You never know what is going to happen either by rough service techs, other service people like cable installers that think plenums and air handlers are there to sit on, or the homeowner stuffing the attic full.

Every time you heat a metal it's molecular state changes and becomes more brittle. The braze material on the other hand is much more rigid than the pipe it's joining creating a leverage point at which the pipe will tend to tear or break if stressed to that point either over time or all at once. ( thats why you are required to have loops at compressor connections ) The effects are amplified depending on the quality of the swage and the copper tubing.

This is all theoretical scenarios and chances are you will never have a problem with a swage joint provided the tech installed everything nice and tidy and with any amount of thought. Less the bull in a china shop cable guy that is. lol May be we are putting too much worry and theory into the whole debate and any decent braze job and you will be just fine either route you decide to take. :cheers:
 
Save
Like Like
#16 ·
garya505 said:
The lines will have to come out horizontally 8" from the coil to clear a humidifier bypass duct, then turn straight up vertically for 5 feet to the ceiling.
Click to expand...
Hopefully they can/will bend "using a bender" the copper for the vertical up run, vs using a 90° fitting.
 
Save
Like Like
Discussion starter · #17 ·
Rcb2875 said:
I believe the risk of a bad swage doesn't exist in the material holding the pressure, but lies with the line having to bear outside stress from say, someone having to adjust the unit or someone bumps or pulls on the line, etc. Also depends if bump or pull on the pipe will cause to pipe to twist or bend at the joint. You never know what is going to happen either by rough service techs, other service people like cable installers that think plenums and air handlers are there to sit on, or the homeowner stuffing the attic full.

Every time you heat a metal it's molecular state changes and becomes more brittle. The braze material on the other hand is much more rigid than the pipe it's joining creating a leverage point at which the pipe will tend to tear or break if stressed to that point either over time or all at once. ( thats why you are required to have loops at compressor connections ) The effects are amplified depending on the quality of the swage and the copper tubing.

This is all theoretical scenarios and chances are you will never have a problem with a swage joint provided the tech installed everything nice and tidy and with any amount of thought. Less the bull in a china shop cable guy that is. lol May be we are putting too much worry and theory into the whole debate and any decent braze job and you will be just fine either route you decide to take. :cheers:
Click to expand...
Ya, that's what I was thinking about, future work causing stress (i.e. the bull in the china shop).

Mr Bill said:
Hopefully they can/will bend "using a bender" the copper for the vertical up run, vs using a 90° fitting.
Click to expand...
Yes, there's plenty of room for a nice tubing bend. It has to come out about 8" from the front of the coil to clear a humidifier bypass duct.
 
Discussion starter · #18 ·
The last question (I hope): With a reducing coupler vs a bushing, would the 3/4 end of the coupler fit over the line or inside the line? Seems like if it fit inside the line then the I.D. would be smaller, creating a slight restriction at that point.
 
#19 ·
With a reducing coupling, a stub piece of 7/8 would be required to join the coupling to the swagged coil stub. With the bushing, it inserts into the coil stub and the line inserts into the bushing with no loss of inside diameter.
 
Discussion starter · #20 ·
heaterman said:
With a reducing coupling, a stub piece of 7/8 would be required to join the coupling to the swagged coil stub. With the bushing, it inserts into the coil stub and the line inserts into the bushing with no loss of inside diameter.
Click to expand...
Thanks for the clarification. I get it now. With the stub, the reducing coupling would be the same as used to join a 3/4 and 7/8 line. But now with the stub, it seems like you would have 3 brazed connections. So, why not just put in a 7/8 stub, then swage the 3/4 slightly to fit inside the stub. I figure 7/8 tubing has an I.D. of about .785 assuming a 0.045 wall thickness.

Hmmm, the 7/8 OD x 3/4 ID bushing is looking like like a "neater" solution.
 
1 - 20 of 49 Posts
You have insufficient privileges to reply here.
About this Discussion
48 Replies
21 Participants
Last post:
Cooked
HVAC-Talk: Heating, Air & Refrigeration Discussion
posts
5M
members
275K
Since
2000
The #1 HVACR Community
Full Forum Listing
Explore Our Forums
AOP Residential HVAC/Refrigeration(Beenthere Zone) General Discussion Tech to Tech Chat - Residential Controls Refrigeration & Ice Making