Mitsubishi Electric SEZ-KD low-static slim ducted indoor units (with SUZ-KA outdoor units): quick sheet

Covers: Mitsubishi Electric M-Series SEZ-KD horizontal ducted (slim, low-static) indoor units, e.g. SEZ-KD09NA4, SEZ-KD12NA4, SEZ-KD15NA4, SEZ-KD18NA4 (revision suffixes such as NA4R1), paired with SUZ-KA single-zone inverter heat pumps (e.g. SUZ-KA09NA) or used on MXZ multi-zone outdoor units. The two digits after KD are nominal capacity in kBtu/h. R-410A, flared connections. Search terms: SEZ-KD09NA4, SEZ-KD12NA4, SUZ-KA09NA, Mitsubishi slim duct, SEZ-KD static pressure.

Single sourceBrands: Mitsubishi Electric5 components

A 7-7/8 in tall concealed ducted unit for short duct runs (one or two rooms), with two sirocco wheels on a DC brushless motor and selectable low external static. Faults are read on the wired controller or by the LED blink method and use Mitsubishi's P/E/U code family. Most problems come from duct design (too much static for a low-static unit), filter and drain issues, and S1-S2-S3 interconnect wiring.

Safety first

S1-S2 carries line voltage from the outdoor unit: lock out the outdoor disconnect.
Refrigerant work is blocked: EPA 608-certified technician.

How it works

The outdoor unit powers the indoor unit through the interconnect: S1-S2 carry 208/230 V AC and S2-S3 carry the 24 V DC communication signal (Mitsubishi submittal).

The DC brushless blower has three speeds; the SEZ-KD09 submittal lists 194-247-317 CFM dry (Lo-Med-Hi) and external static settings of 0.02 to 0.20 in. w.c.

Indoor operating limits listed for the 09 size: cooling 67-90 °F DB intake; heating 70-80 °F DB intake. Outdoor: cooling 14-115 °F, heating -4 to 75 °F (SUZ-KA09NA pair).

Components & tests

Unlock all 5 components, specs, service mode and teardown

Full library + AI assistant + the OnCall Tech app for iPhone & Android. $34.90, one time.

Get lifetime access

Official manufacturer documentation

Always confirm values against the tech sheet for the exact model.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): Two ductless mini-split outdoor units on a house wall, one on a steel wall bracket, with the insulated line set running into the wall by Pedalito, CC0

Diagnostic guides for this appliance

Guide · Air Conditioner

PTAC not cooling (fan runs, air not cold)

Most PTAC no-cool calls are airflow (filter, coils), a wrong control setting or a failed compressor start component. Rule those out before suspecting the sealed system.

6 steps ~60 minmoderate

Guide · Air Conditioner

PTAC not heating (electric heat or heat pump)

PTACs heat with electric strip heat, a heat pump, or both. Heat pump models switch to strip heat in cold weather. Check settings, then the heater element and its limits, then the reversing valve.

5 steps ~60 minmoderate

Guide · Air Conditioner

PTAC error codes: how to read and clear them

Most PTAC brands store fault codes that can be shown with a button combination on the control (for example, on GE Zoneline (2019 technical service guide) you hold FAN and the red AUX button together while the unit is OFF, and AUX clears stored faults; other models use other sequences, so use the model's tech sheet). Read the active code, fix the cause, then clear it.

4 steps ~20 mineasy

Other air conditioners manuals

Manual · Air Conditioner

Carrier Infinity Greenspeed 24VNA6 air conditioner and 25VNA4 heat pump (variable speed): quick sheet

Carrier Infinity Greenspeed Intelligence variable-speed outdoor units: 24VNA6 air conditioner (up to 26 SEER) and 25VNA4 heat pump (up to 24 SEER, up to 13 HSPF), 2-5 ton. Nomenclature from the service manual: 24 = AC, 25 = HP; V = variable speed; N = Infinity series; A = Puron (R-410A); 6 / 4 = SEER tier; two digits = nominal capacity (e.g. 36 = 36,000 BTU/h); voltage digit 3 = 208/230-1; compressor ID 4 = variable-speed scroll, 5 = variable-speed rotary. Serial format: week + year + plant letter + sequence (e.g. 0118E00001). Other 24VNA families (24VNA0, 24VNA9) use different software and code lists.

5 components4 common failuresCarrier

Manual · Air Conditioner

Trane XV20i / XV18 variable-speed outdoor units (4TTV0 AC, 4TWV0 heat pump, ComfortLink II): quick sheet

Trane variable-speed TruComfort / ComfortLink II communicating outdoor units: 4TTV0 air conditioners (XV20i family, e.g. 4TTV0024A1000C, 4TTV0036, 4TTV0048, 4TTV0060, 4TTV0061) and 4TWV0 heat pumps (Service Facts 4T-V0-SF). They use an Integrated Variable Speed Control (IVSC) board and a Communicating Display Assembly (CDA) in the outdoor unit. Distributor listings note several 4TTV0 revisions; confirm the full model on the nameplate before ordering parts. Single-stage XR14/XR16 units are on a separate sheet.

4 components3 common failuresTrane

Manual · Air Conditioner

Lennox XC21 air conditioner and XP21 heat pump (Dave Lennox Signature, iComfort-enabled): quick sheet

Lennox XC21 (air conditioner, service literature Corp. 1007-L2) and XP21 (heat pump, Corp. 1031-L7), 2, 3, 4 and 5 ton, R-410A, expansion valve indoor coils only. Both use an A175 main control (outdoor control part number 101798-xx) that works in communicating (iComfort) or conventional 24 V mode, plus a separate fan motor control. The XP21 literature describes a two-stage scroll compressor; the 2018 XC21 literature describes the compressor as one-stage while the same control section covers two-stage units, so confirm staging on the nameplate. For ML14XC1/EL16XC1 single-stage units see the separate sheet.

4 components3 common failuresLennox