R-Pro › Field cases › Air conditioning
AC New Install — Line Set Length and Height Limit (Manufacturer Manual)
Likely causes
Step 1 — Apply length limit by single-zone vs multi-zone type
Check: Single-zone: typically 15–20 m (50–66 ft). 9–12k BTU budget: 15 m. 18k+: 20–25 m. Multi-zone 27k BTU: 60 m total equivalent, 23 m per zone. 36k BTU: 80 m total. VRF: 100–200 m. Default factory-charge line length: 7–7.5 m (verify manual). Excess length needs additional g/m charge.
What to do: Verify max line length per model from manufacturer table. Beyond default charge length (7–7.5 m) = add g/m supplemental charge. Near limit = consider next-tier model or VRF. Exceeding limit voids warranty + 80% chance of compressor failure within 5 years.
Step 2 — Height difference limit and equivalent length conversion
Check: Single-zone height: typically 10–15 m (33–50 ft). VRF: 50–110 m. Each 5 ft (1.5 m) rise = 5 ft additional equivalent length. One bend = 0.3–0.5 m equivalent add. One branch = 0.5–1 m. Exceeding limit = compressor overload, oil return failure, 30% capacity loss.
What to do: Measure outdoor/indoor height difference. Beyond single-zone limit (10–15 m) = consult manual. Multi/VRF 50–110 m possible. Equivalent length: each bend = 0.3–0.5 m, each branch = 0.5–1 m. Exceeding height limit = oil-return failure → compressor damage.
Exceeding limit = warranty void (per manufacturer). Near limit = consider next tier or VRF. Relocate outdoor unit to shorten if possible. Manual always takes priority (not field guides). Over-length installation = 80% chance of compressor failure within 5 years.
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