Ductless Mini-Split Systems Flashcards

What is the primary advantage of a ductless mini-split system over a central ducted system?

Answer: Elimination of duct losses (typically 20-30% of energy in ducted systems) and ability to serve spaces without existing ductwork

Ductless mini-splits eliminate duct losses (typically 20-30% of system energy in leaky or poorly insulated ductwork), enabling direct zone-level conditioning. They are ideal for additions, converted spaces, and buildings where installing ductwork is impractical or too costly.

What does 'inverter-driven' compressor technology in mini-splits provide?

Answer: Variable-speed compressor operation that modulates cooling/heating capacity to exactly match the load, improving efficiency and comfort

Inverter-driven compressors vary their speed (and therefore capacity) to precisely match the zone's load. Unlike on/off cycling, the compressor ramps down at part load, reducing energy consumption, eliminating temperature swings, and improving efficiency — especially at part load (which is most of operating hours).

What is the typical line set for a ductless mini-split system?

Answer: Refrigerant lines (liquid and suction), electrical power/signal wiring, and a condensate drain line

A mini-split line set consists of: refrigerant lines (small liquid line + larger insulated suction/gas line), communication/control wiring (typically 4-wire or signal wire between indoor and outdoor units), and a condensate drain line from the indoor unit.

What is the maximum typical line set length for a standard residential ductless mini-split?

Answer: 50-75 feet (15-23 m)

Most standard residential mini-splits support line set lengths of 50-75 feet (15-23 m) without additional refrigerant charge. Maximum lengths vary by manufacturer (often 98-164 feet). Longer runs require additional refrigerant charge (per manufacturer specification) and may reduce capacity.

What is a 'multi-zone' mini-split system?

Answer: One outdoor unit connected to multiple indoor units (2-8 zones) via individual refrigerant branch piping

A multi-zone (multi-split) system connects one outdoor unit to multiple indoor units (typically 2-8 units), each serving an independent zone with individual temperature control. Refrigerant branches from the outdoor unit to each indoor unit via a header or individual line sets.

What is the minimum ambient operating temperature for most standard heat pump mini-splits in heating mode?

Answer: 17°F (-8.3°C)

Standard heat pump mini-splits typically maintain rated heating capacity to about 17°F (-8.3°C) outdoor ambient, with some capacity to around 5°F (-15°C). 'Cold climate' or 'hyper-heat' mini-splits can maintain significant heating capacity down to -13°F to -22°F (-25 to -30°C).

What type of indoor unit is most commonly used in residential ductless mini-split installations?

Answer: Wall-mounted high-wall unit

The wall-mounted high-wall unit is the most common residential ductless indoor unit. It mounts high on the wall, delivers conditioned air across the room with a wide sweep, is the lowest cost option, and is easiest to install. Ceiling cassettes and floor units are also available for specific applications.

How is the refrigerant in a mini-split system typically charged at installation?

Answer: Pre-charged at the factory for standard line set lengths; additional refrigerant is added only if line set exceeds the standard length

Mini-splits are factory pre-charged with sufficient refrigerant for line set lengths up to a specified length (usually 15-25 feet). For longer line sets, technicians must add refrigerant per the manufacturer's specification (typically a fixed amount per foot of additional length).

What is the purpose of the 'auto-restart' feature in mini-split systems?

Answer: Restarts the system automatically after a power outage, returning to previous settings

Auto-restart automatically resumes operation after a power outage, returning to the previously set mode, temperature, and fan speed. This eliminates the need to manually reprogram the remote control after every power interruption, important in areas with frequent outages.

What is 'heating mode defrost' in a mini-split heat pump, and what causes it?

Answer: A temporary reverse-cycle operation that melts frost from the outdoor coil when it accumulates during heating mode

During heating mode in cold, humid weather, the outdoor coil acts as the evaporator and can freeze over with frost. The mini-split initiates a defrost cycle by temporarily reversing to cooling mode, sending hot refrigerant to the outdoor coil to melt the frost. The indoor unit may blow cool air briefly during defrost.

What is the typical SEER2 range for modern high-efficiency ductless mini-splits?

Answer: 20-30+ SEER2

Modern high-efficiency ductless mini-splits typically achieve SEER2 ratings of 20-30+, with some premium units exceeding 33 SEER2. This is significantly higher than most ducted central air systems (SEER2 13.4-18+), due to inverter compressors and the elimination of duct losses.

What is the correct procedure for connecting refrigerant line sets on a mini-split?

Answer: Use flare fittings: cut, deburr, flare, and torque connections to manufacturer specification using a torque wrench

Mini-split refrigerant line sets use flare connections. The copper tubing must be cut cleanly, deburred inside and out, then flared with a quality flaring tool. Connections are tightened to the manufacturer's specified torque with a torque wrench — over-tightening cracks flares, under-tightening causes leaks.

What is a '4-way cassette' indoor unit in a mini-split system?

Answer: A ceiling-recessed unit that distributes air in 4 directions (360°) for even room coverage

A 4-way cassette (ceiling cassette) is a ceiling-recessed indoor unit with a decorative grille that distributes conditioned air in four directions simultaneously. This provides even coverage for large open spaces without wall space requirements. The only visible part is the grille in the ceiling.

What communication protocol do many modern mini-split systems use between indoor and outdoor units?

Answer: Proprietary serial digital communication over a dedicated wire pair

Most mini-splits use proprietary digital serial communication between indoor and outdoor units, typically over a dedicated 2-3 wire communication bus. This allows the outdoor unit to optimize compressor speed based on individual zone demands and provide detailed diagnostics.

What is the purpose of vacuuming a mini-split system before charging?

Answer: Both B and C — remove air/moisture and verify leak-free

Evacuation (deep vacuum to 300-500 microns) removes both air/moisture from the system AND verifies the system is leak-free (a proper vacuum holds without rising). Both objectives must be met before charging with refrigerant.

What happens if mini-split refrigerant line sets are installed without insulating the suction line?

Answer: The suction line gains heat from ambient air, reducing system efficiency and potentially causing liquid floodback

The suction (gas) line must be insulated to prevent heat gain from the surrounding environment. Uninsulated suction lines absorb heat from hot ambient air, reducing cooling efficiency. In humid conditions, the cold uninsulated line can also condense ambient moisture and drip.

What does a mini-split's 'self-cleaning' or 'auto-clean' feature do?

Answer: After cooling, heats the indoor coil to dry residual moisture and prevent biological growth

The auto-clean feature (after cooling mode) temporarily runs the indoor unit in heating mode to dry the indoor coil and drain pan, inhibiting biological growth (mold, bacteria) that causes dirty sock syndrome and poor air quality.

What is the required clearance above and around a mini-split outdoor unit for proper airflow?

Answer: Manufacturer-specified clearances (typically 6-12 inches on sides, 12-24 inches in front for discharge, and clear above)

Mini-split outdoor units require manufacturer-specified clearances for proper airflow and serviceability. Typical requirements: 6-12 inches on sides and rear, 12-24+ inches in front of the discharge (or above for vertical discharge), and unobstructed overhead. Restricted airflow raises head pressure and reduces efficiency.

What does the 'sleep mode' or 'quiet mode' function do on a mini-split?

Answer: Gradually adjusts temperature setpoint and reduces fan speed to minimize sound during sleeping hours

Sleep mode gradually adjusts the setpoint (increases cooling setpoint slightly as people sleep cooler) and reduces fan speed to minimize noise. The quieter operation and slightly relaxed setpoint balance comfort with reduced energy consumption during sleeping hours.

What is a 'branch box' (or 'BS unit') in a VRF/multi-split system?

Answer: A refrigerant flow distribution device that splits refrigerant from one outdoor unit to multiple indoor units, enabling simultaneous heating and cooling in different zones

A branch box (BS unit) is used in advanced VRF systems to split refrigerant flow and enable simultaneous heating and cooling in different zones. Unlike simple multi-split systems, branch boxes with heat recovery functionality allow some indoor units to cool while others heat, improving efficiency.