If you've already chosen a MRCOOL DIY mini split system and purchased a 35ft pre-charged lineset like the DIY35-1412C, you're probably feeling confident about your install. But what happens when your total line route turns out to be longer than expected?
Don’t worry—you’re not alone. I ran into the same problem. Thankfully, MRCOOL built a solution that makes extending a lineset just as DIY-friendly: the MRCOOL DIY Coupler Kit.
In this guide, I’ll walk you through when to use an extension, how to do it right, and what to avoid.
📅 Why You Might Need More Than 35 Feet
You measure your installation route and think 35 feet should do it. But here are a few things that often sneak up on homeowners:
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Elevation changes from the ground-mounted condenser to a second-story room
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Routing around soffits, joists, or ductwork
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Wall penetration depth and bends
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Extra slack needed for gentle curves and drip loops
"I measured 34 feet and thought I was in the clear. After adding the route around my deck and up through the attic, I ended up 8 feet short." — Mark
Tip: Always add 10–15% extra to your measured distance for real-world routing.
🔗 Use this Line Set Estimator Tool to help plan better.
🛏️ Meet the MRCOOL DIY Coupler Kit
The MRCOOL Coupler Kit allows you to safely extend two pre-charged linesets while preserving system pressure and refrigerant integrity. It uses quick-connect fittings, just like the rest of the MRCOOL DIY system.
What’s Included:
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Pre-sealed valve coupler
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Threaded quick-connect fittings
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Double gasket seal
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Instruction guide with torque specs
Key Benefits:
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No vacuuming required
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No refrigerant loss
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Compatible with 1/4" liquid and 1/2" suction lines (standard on most MRCOOL systems)
🔗 More info on official MRCOOL accessories
📗 How to Combine Line Sets with a Coupler Kit
Here’s how you can extend your reach using a second lineset and a coupler:
Example Combinations:
| Primary Line | Extension | Total Length |
|---|---|---|
| 35ft | 16ft | 51ft |
| 35ft | 25ft | 60ft |
| 25ft | 25ft | 50ft |
| 16ft | 16ft | 32ft |
Maximum recommended total run: 75ft (depending on system BTUs)
Compatibility Note:
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Works with MRCOOL linesets that use 1/4" x 1/2" fittings
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Do NOT use with linesets requiring 3/8" suction lines (like 9k BTU handlers)
⚡ Mistakes to Avoid When Extending Linesets
Mark here again. I made a few avoidable errors when extending my own lineset. Learn from me:
❌ Mistake #1: Installing the Coupler in a Tight Spot
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I put mine behind vinyl siding—hard to torque properly
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Fixing a leak there would have meant tearing the siding back off
Tip: Always install the coupler in an accessible area for maintenance
❌ Mistake #2: Forgetting Support Brackets
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My lineset sagged between clamps, putting stress on the connection
Tip: Use pipe clamps every 4–6 feet on both sides of the coupler
❌ Mistake #3: Not Pressure Testing
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I skipped leak testing and paid for it with a low refrigerant error 2 days later
Tip: Always test for leaks with soapy water before sealing up the route
🚀 Real-World Walkthrough: Mark’s Coupler Extension
When I extended my lineset:
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My original 35ft line fell short by 6 feet
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I used a 16ft lineset + DIY coupler kit to create a 51ft run
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Took me about 25 minutes total
Key Steps:
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Measured exact length needed
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Cleaned both fitting ends thoroughly
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Aligned and threaded the quick-connects
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Used a torque wrench to tighten to MRCOOL specs
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Secured both ends with brackets
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Tested with leak spray
✅ Result: No leaks, seamless operation, and finished the install in one afternoon.
🧠 Expert Tips for Clean Extensions
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Use a torque wrench (33–35 ft-lbs is typical for MRCOOL fittings)
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Do NOT bend or twist the coupler during install
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Always leave 6" of straight line before and after the coupler
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Label your linesets so you don’t confuse suction/liquid lines
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Seal your coupler connection with foam wrap + UV cover
📦 Extend or Replace? How to Decide
Extend your line if:
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You’re within 20–25ft of the goal
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You already have a MRCOOL pre-charged lineset
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Your BTU capacity supports longer refrigerant flow
Replace your line if:
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You need more than 75ft total
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Your air handler uses a different size (e.g., 3/8" suction)
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You damaged your current lineset beyond repair
📣 Final Thoughts from Mark
Extending your MRCOOL lineset with a coupler kit is easier than it sounds. But it only works well if you take the time to:
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Measure accurately
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Support your connections properly
The coupler kit saved my project—and saved me from having to rip out and replace the original lineset.
"Don’t panic if your 35ft line won’t reach. MRCOOL made a smart, safe way to finish the job. You just need the right kit, a torque wrench, and a little patience."
In the next topic we will know more about: Can You Bury the MRCOOL Pre-Charged Lineset? Outdoor Routing Tips & Pitfalls
