MRCOOL® DIYCOUPLER-3858K75 — DIY Coupler Set (3/8″ + 5/8″) with 75ft Communication Wire

MRCOOL® DIYCOUPLER-3858K75 — 3/8″ and 5/8″ Coupler Set with 75 ft Communication Wire

DIYCOUPLER-3858K75 joins two MRCOOL DIY quick-connect line sets on a 24K or 36K zone and includes 75 feet of communication wire for the longer electrical run. This is the standard-wire version of the kit — if you want the factory-terminated DIY Pro Cable instead, order DIYCOUPLER-3858K75C.

Key features

• Two machined brass couplers — 3/8″ liquid line and 5/8″ suction line
• 75 ft communication wire included — covers the extended run between indoor and outdoor units
• Quick-connect design — mates to MRCOOL DIY flare fittings, no brazing required
• For 24K and 36K indoor units — the capacities that use 3/8″ x 5/8″ lines
• Extends a single zone — combine two line sets when one length will not reach

Wire version versus Pro Cable version

This part ships with plain 75 ft communication wire, which is field-terminated at both ends. DIYCOUPLER-3858K75C ships with the MRCOOL DIY Pro Cable, which is pre-terminated for plug-and-play connection. The couplers are the same in both kits; only the cable differs.

Line length limit

MRCOOL specifies a maximum of 75 feet of total line length per zone across the two coupled line sets.

What is in the box

• 1 × DIYCOUPLER-38 (3/8″ coupler)
• 1 × DIYCOUPLER-58 (5/8″ coupler)
• 1 × 75 ft communication wire

Frequently asked questions

Is the DIY Pro Cable included with this part?

No. This kit includes plain communication wire. For the Pro Cable, order DIYCOUPLER-3858K75C.

Can I use this on a 12K or 18K indoor unit?

No. Those units use 1/4″ x 1/2″ lines and need the DIYCOUPLER-1412 series.

Does the wire need to be terminated in the field?

Yes. Standard communication wire is stripped and connected at the terminal blocks on both units, following the MRCOOL wiring diagram.

Do I need a vacuum pump after coupling two line sets?

No. The quick-connect fittings on MRCOOL DIY line sets and couplers are designed to be assembled without evacuation. Leak-check every joint after assembly.

How many couplers come in the kit?

Two — one for each refrigerant line.

Why buy from Cedars HVAC

• Genuine MRCOOL OEM parts — never aftermarket substitutes
• Contractor-friendly pricing on every line set and accessory
• Fast nationwide shipping from our Miami, Florida warehouse
• Financing available at checkout

Shipping and returns

Most orders ship the same or next business day from Cedars HVAC in Miami, Florida. Standard ground shipping covers the continental United States, and expedited options are available at checkout. Returns are accepted within 30 days on unopened, uninstalled parts — see our return policy for full details.