Troubleshooting Ride-Along: Do I Need New Refrigerant Lines With a New AC?
Location: B Section — Palm Coast, Florida
Job: Full AC system replacement with existing refrigerant lines running underground.
Today’s homeowner had a very reasonable question.
We’re replacing the air conditioner.
The refrigerant lines connecting the indoor and outdoor equipment run underground.
So:
“Do we need to replace those too?”
No.
Not automatically.
A new air conditioner does not mean every piece of copper attached to the old one suddenly expires.
Think about it this way:
You don’t repipe your entire house because you bought a new water heater.
Same idea.
But before we’re trusting an existing underground line set with a brand-new AC, it has to prove it deserves to stay.
The B Section Install
This Palm Coast house had an existing refrigerant line set running underground between the indoor and outdoor equipment.
Replacing it was possible.
We could abandon the underground copper and find another route—often up through the attic and back down to the condenser.
We’ve done exactly that on other installations.
But that means more materials.
More labor.
More holes.
More attic time.
And potentially more cost for the homeowner.
So our question wasn’t:
“Can we replace it?”
Of course we can.
Our question was:
“Is there actually anything wrong with it?”
Has It Ever Leaked?
This is one of the first things we want to know.
Has this system had refrigerant leaks before?
Has someone repeatedly added refrigerant?
Has the line set itself ever been repaired?
Do we have any reason to suspect the underground copper?
If the homeowner tells us:
“Every summer somebody adds three pounds of refrigerant and nobody knows where it goes.”
Okay.
We’re going to have a considerably different conversation.
But this homeowner didn’t have a history pointing toward a leaking underground line set.
That’s good.
It still doesn’t get the copper a free pass.
Before the New System Starts, We Pressure Test It
When we’re reusing an existing refrigerant line set, we don’t just hook the brand-new equipment to it and hope for the best.
We test it.
The existing piping has to be appropriate for the new equipment, properly prepared, and hold pressure without leaking.
That’s especially important with underground lines.
Because once we release refrigerant into the new system, we’d really prefer that refrigerant remain inside the system.
Call us picky.
So before startup, the existing line set gets pressure tested.
If it holds?
Great.
If it doesn’t?
Now we have evidence that something is wrong.
And the plan changes.
What If It Fails the Pressure Test?
Then we’re not using it.
That’s when the conversation becomes:
Can the existing line be repaired?
Is the failure accessible?
Or does it make more sense to abandon the underground line set and install new copper using another route?
On many Palm Coast homes, that may mean going overhead through the attic.
Not because attic crawling is one of our hobbies.
It isn’t.
But because accessible new copper beats knowingly connecting brand-new equipment to a leaking underground line.
“But Isn’t the Old Copper… Old?”
Sure.
So are plenty of copper water pipes in houses all over Palm Coast.
Age alone doesn’t tell us that copper tubing is leaking.
Condition matters.
History matters.
Sizing matters.
Compatibility with the new equipment matters.
And testing matters.
We don’t replace a line set simply because it was connected to the previous air conditioner.
That’s how you turn an AC replacement into unnecessary construction work.
If there’s a legitimate reason to replace it?
We’ll replace it.
If there isn’t?
We’re not inventing one.
There Are Times We’d Recommend New Lines Anyway
Reusing a line set isn’t automatic either.
We may recommend replacement if:
- it leaks
- it has a history of leaks
- the piping is damaged
- the line sizes aren’t appropriate for the new equipment
- there’s contamination from a previous system failure
- the manufacturer doesn’t permit that piping/application
- the existing route or condition creates another legitimate installation problem
That’s a completely different statement from:
“You’re getting a new AC, so you need new copper.”
Maybe you do.
Maybe you don’t.
Let’s look at the copper.
Why Underground Lines Make Homeowners Nervous
Understandably.
You can’t see them.
We can’t visually inspect the entire run.
And if one develops a leak underneath the slab, we’re not exactly sending Jackson down there with a flashlight.
So testing becomes particularly important.
We can’t see every inch of the copper.
But we can ask the entire line set a very useful question:
Can you hold pressure?
If the answer is yes, and everything else about the piping is appropriate for the new system, we have evidence supporting reuse.
If the answer is no?
Now we have a reason to replace or reroute it.
The B Section Verdict
Job: Full AC system replacement.
Existing refrigerant lines: Underground.
History of line-set leaks: None reported.
Does a new AC automatically require a new line set?
No.
Our plan: Reuse the existing refrigerant piping if it meets the requirements for the new equipment and passes our pre-start pressure testing.
If it fails?
Stop.
Find the leak or abandon the underground piping and install a new line set.
That’s considerably different from replacing thousands of dollars worth of work because:
“Well, the copper is old.”
The Bigger Lesson
When you’re replacing an air conditioner, ask what actually needs to be replaced.
Some things absolutely should be.
Others need to be inspected and tested.
Your refrigerant line set falls into that second category surprisingly often.
New AC doesn’t automatically mean:
new copper.
Just like a new water heater doesn’t mean:
Congratulations! We’re repiping your house.
If the existing refrigerant lines are appropriate for the new equipment, have no concerning history and pass the required testing, there may be absolutely no reason to tear into your house just to replace perfectly usable copper.
And if they don’t pass?
Then we’ll deal with that problem when we actually have evidence that the problem exists.
Test first. Tear stuff apart second.