Does MRCOOL DIY® Need a Vacuum Pump? How Quick Connect® Line Sets Work
- No vacuum pump, flare tool or gauges. The DIY® line set is pre-charged and sealed.
- Connect with two wrenches, open the valves with a 5 mm Allen key, leak-check with soapy water.
- No Teflon tape, and connect each fitting only once.
If you've read anything about mini splits, you've heard that the system has to be "pulled into a vacuum" before it runs. That's true for traditional systems. It's not true for MRCOOL DIY®.
Why traditional mini splits need a vacuum
On a normal install, the copper lines are cut and flared on site, so they're full of air and moisture. A technician hooks up a vacuum pump and micron gauge and pulls all of that out before releasing refrigerant. Moisture left behind turns into acid and ice inside the system.
How the Quick Connect® line set skips that step
The DIY® line set is made, filled and sealed at the factory. Each end has a sealed fitting designed to make its connection as you tighten it onto the matching port, so the inside of the line is never opened to outside air. Once both ends are on, you open the condenser's two service valves and the system is complete.
MRCOOL · 2:21How to connect MRCOOL's pre-charged Quick Connect® line setHow to connect it right the first time
- Dry weather, clean threads. Moisture or grit in a fitting is the number one cause of slow leaks.
- Caps on until the last second. The colored caps match their partners, so use them to line things up.
- Start by hand. Thread a few turns square to the port so it doesn't cross-thread.
- Two wrenches. Hold the fitting body still with one and turn the nut with the other.
- Snug, then a little more. With an HVAC torque wrench, use MRCOOL's spec: 18–20 lb-ft for 3/8 in, 30–35 for 1/2 in, 45–50 for 3/4 in, 60–65 for 1 in. Without one, go just past snug. Don't crank it.
- Open the valves. Caps off, 5 mm Allen key, counter-clockwise until it stops. Caps back on.
- Soapy water on all four joints. Then check again after the system has run for a while, because pressures change once it's running.
Which line set fits my system?
| System | Line size | Our 25 ft set |
|---|---|---|
| 6K, 9K, 12K | 1/4 × 3/8 in | DIY25-1438 |
| 18K | 1/4 × 1/2 in | DIY25-1412 |
| 24K, 36K | 3/8 × 5/8 in | DIY25-3858 |
Single-zone DIY® systems already include a 25 ft set. You only buy one separately for multi-zone indoor units or to go longer. See our line set length guide.
MRCOOL · 1:24No-Vac® Quick Connect® line set featuresWhat about the bigger ducted systems?
MRCOOL's Universal® ducted heat pumps use a separate NO-VAC® Quick Connect® line set (3/8 × 3/4 in) that works the same way. You'll find them right on our ducted systems page.
Every single-zone DIY® 5th Gen bundle ships with a 25 ft Quick Connect® set and the DIYPRO® cable. For longer runs, add an extension and a coupler kit.
Get the DIY Mini Split Install Handbook
All 13 steps, the clearance, torque, wiring and line set tables, QR codes to every MRCOOL video, a sign-off checklist, and a 10% off code for your system.
