Avoiding Common Mistakes When Running a 50 ft Lineset Through Walls or

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1. Why It Matters for Mike

For DIYers like you, Mike, running a 50 ft MRCOOL pre-charged lineset through walls or attics is a practical route—but it comes with traps that can derail performance, warranty, and efficiency. Let’s tackle this head-on with pro insights.

🧭 2. Major Mistakes to Watch For

a. Burying the Lineset Inside Walls

MRCOOL strongly advises against concealing lines within walls. Hidden lines are hard to access for leak checks or repairs (Mr Cool DIY 9k indoor unit line set connection)
Service issues often require wall demolition — a messy, costly mistake.

b. Sharp Bends & Kinks

Copper tubing doesn’t like tight bends. Obstructed flow can reduce efficiency and burn out the compressor MRCOOL.
Always maintain the minimum bend radius—chances are about 6 inches for 1/2″ lines.

c. Ignoring Insulation & Temperature Extremes

Running lines through an uninsulated attic exposes them to extreme heat or cold. This leads to condensation, frost, or refrigerant imbalance

d. Vertical Elevator Runs Without Planning

A straight-up run may trap oil in the refrigerant lines, reducing efficiency. Keep total vertical rise within manufacturer limits and follow oil-trap guidelines

e. Overlooking Securing & Support

Lines must be firmly anchored—ideally a support every 4 ft, plus extra before and after turns (Question about running mini split tubing in attic)

🛠️ 3. Planning the Run

a. Map the Route

Trace the path of your 50 ft lineset—through the wall sleeve, across attic joists, and down exterior walls.
Avoid routing next to plumbing, electrical conduits, or areas that experience movement.

b. Measure Smart

Always allow 5–10 ft extra for slack, coils, or miscalculations. Remember, MRCOOL recommends coiling excess exterior behind the condenser—not cutting it.

c. Evaluate Temperature Zones

If attic temperatures vary widely, consider adding insulation along the lines or using an insulated chase.

🔧 4. Installation Best Practices

a. Wall Hole Setup

Drill a 3.5″ hole with a slight downward slope toward the outdoors to prevent water ingress
Install the included wall sleeve for structural support and a clean finish.

b. Attic Routing & Elevation

Avoid total vertical rises above 25 ft unless using MRCOOL’s vertical-line allowance; installing an oil trap may be required (Complete Guide to MRCOOL Pre-Charged & No-Vac Line Sets)
Anchor lines every 4 ft and at top/bottom of vertical climbs.

c. Bend & Loop Carefully

Use gentle curves—no tight 90-degree bends.
Keep loops uniform and spacious to prevent performance issues .

d. Rigorous Insulation

In hot attics, insulate tubing or run it within insulated ducting to prevent heat soak (Common Challenges and Solutions for Installing a Mini Split AC System in an Attic)

e. Avoid Hidden Couplers

Do not hide any coupler connections in walls. They need to be visible and testable.

f. Ensure Proper Drain Line Slope

Keep condensate drain angled down with no S-traps to prevent pooling.

✅ 5. Common Troubleshooting Scenarios

Scenario	Symptom	Likely Cause	Remedy
Poor cooling in summer	Temperature too high indoors	Insulation issues or heat soak	Add line insulation
Intermittent frost on lines	Ice accumulation on tubing	Cold attic with insufficient insulation	Insulate lines, adjust route
Compressor strain or noise	Hissing/sound during start-up	Oil trap or sharp bends	Install vertical loop/trap; smooth bends
Leak during annual check	Refrigerant escaping	Hidden coupler or kink	Exposed lines only; test connections