FieldBench
Models
Lennoxac

SL28XCV

Signature · variable-capacity inverter AC

Lennox Signature variable air conditioner (SL28XCV; SL25KCV / SL25XCV in the field). Outdoor inverter + iComfort. No reversing valve. Charge is weigh-in. Not XC21 two-stage.

Not XC21 / EL18XC1 two-stage scroll. Not EL18XCV Elite inverter (different drive / rating). Not a furnace E223.

Diagnose this modelInstall notesBoard cross-refField wiring

Drive

Inverter scroll · variable capacity

Bus

iComfort communicating

Charge

Weigh-in + line-set

This board

Signature outdoor inverter — AC only

  • iComfort events + outdoor drive.
  • No dual cap. No defrost.
  • SL25KCV is this variable family, not XC21.

iComfort last events.

Universal swap

No universal

Lennox SL28XCV outdoor. No furnace IFC universal. Replace the OEM outdoor control / contactor / drive by the silk.

Silk: SL28XCV

White-Rodgers

—

ICM

—

Honeywell

—
  • Indoor furnace universals (50A55, 50M56U, ICM282B, ICM2811, S9200U). This is not an IFC.
  • Do not ‘adapt’ a furnace board to an outdoor inverter, defrost PCB, or contactor.

After you pull the dead card

  1. 1Photograph the outdoor silk. Indoor 50A55 / ICM282B / S9200U do not belong here.
  2. 2Contactor units: replace the contactor / cap / HPS — there is no universal outdoor board.
  3. 3Inverter / communicating outdoors: OEM drive only. There is no White-Rodgers or ICM outdoor universal.

Field wiring

Written landings for Lennox SL28XCV. Not a factory schematic.

iComfort variable AC
I+ / I−R-410A

Lennox EL18XCV / SL28XCV. iComfort S30/S40 on I+ and I−. EL18XC1 is Y1/Y2 two-stage — different diagram.

Written circuit description only — FieldBench does not redraw maker schematics. Example: R to W closes on a heat call; verify 24V at W1 before you change the IFC.

Open manufacturer PDF

This indoor

Signature variable. Same I+/I−. Not XC21 two-stage.

iComfort communicating

S30 / S40 / communicating indoor on I+ I−.

iComfort S30 / S40

R, C, I+, I−. I+ / I− are data.

  • R24V hot24V
  • C24V common24V
  • I+iComfort dataData
  • I−iComfort dataData

Communicating indoor

Same I+ / I−. A 24V Merit indoor is the other landing.

  • I+DataData
  • I−DataData
  • R24V24V
  • CCommon24V

Variable outdoor

Communicating outdoor. No dual cap.

  • I+DataData
  • I−DataData

Outdoor line — inverter drive

208/230 into the drive. No contactor slam. DC bus can stay live after the disconnect.

  • L1Line to the driveLine
  • L2Line to the driveLine
  • GNDEquipment groundLine

Landing

  • DataStat I+/I−indoor I+/I−outdoor

    iComfort data. Not Y.

  • 24VR and C at the stat

    ~24 VAC

  • LineL1 / L2outdoor

    208/230

Prove it

  • iComfort alerts first. Outdoor on the equipment list.
  • I+ / I− landing and polarity. R and C still required at the stat.

Do not

  • Do not use this on EL18XC1 or EL16XC1 / ML14XC1.
  • Do not land Y on I+.

I+ / I− are the published iComfort communicating terminals.

Sequence

  1. 1

    Call

    iComfort requests capacity. Inverter ramps.

  2. 2

    Protect

    HPS / LPS / drive. No defrost.

Faults on this IFC

Step 1, then 2, then 3. Expected reading and the fail branch sit under each check.

Comm

ABCD / outdoor drop

lockout

Drive or bus. Wall control loses the outdoor.

  1. 1 Let it cool, then read the drive LED

    On Lennox SL28XCV overcurrent / overheat is often a dirty coil, a failed OD fan, or a locked compressor — not a dead inverter. Clear airflow, confirm the OD fan, and read the drive LED before you order a control. ABCD landing and polarity, outdoor board power, inverter comms harness.

    Expect: OD fan running. Coil clean. Drive LED decoded from THIS outdoor’s card.

  2. 2 Voltage and compressor windings

    Incoming voltage in range (this plate’s line-voltage code). Compressor windings even, no ground. A shorted compressor will kill a new drive. C still required at the wall control.

    Expect: Balanced windings. No winding to ground. Line voltage stable under load.

  3. 3 Charge and the drive last

    A starved or flooded compressor will overcurrent. Confirm SH/SC and charge weight. Only then condemn the inverter. Indoor must be Infinity-capable. A 24ACC6-style indoor pairing is the wrong mental model.

    Expect: Charge on the nameplate. Drive code gone after a cool-down and a clean coil.

HPS / LPS

Pressure protection

lockout

Still real on an inverter.

  1. 1 Let it cool, then read the drive LED

    On Lennox SL28XCV overcurrent / overheat is often a dirty coil, a failed OD fan, or a locked compressor — not a dead inverter. Clear airflow, confirm the OD fan, and read the drive LED before you order a control. Coil, fan, charge by weigh-in — you do not ‘top off’ a Greenspeed.

    Expect: OD fan running. Coil clean. Drive LED decoded from THIS outdoor’s card.

  2. 2 Voltage and compressor windings

    Incoming voltage in range (this plate’s line-voltage code). Compressor windings even, no ground. A shorted compressor will kill a new drive. Outdoor fan that is actually the inverter-driven fan, not a dual-cap PSC motor.

    Expect: Balanced windings. No winding to ground. Line voltage stable under load.

  3. 3 Charge and the drive last

    A starved or flooded compressor will overcurrent. Confirm SH/SC and charge weight. Only then condemn the inverter. Do not use 24ACC6 piston superheat as the pass/fail.

    Expect: Charge on the nameplate. Drive code gone after a cool-down and a clean coil.

Inverter

Drive overcurrent / overheat

lockout

L5/L4-class faults on the drive.

  1. 1 Let it cool, then read the drive LED

    On Lennox SL28XCV overcurrent / overheat is often a dirty coil, a failed OD fan, or a locked compressor — not a dead inverter. Clear airflow, confirm the OD fan, and read the drive LED before you order a control. Compressor to ground, heat sink, supply voltage. Weigh-in vs nameplate.

    Expect: OD fan running. Coil clean. Drive LED decoded from THIS outdoor’s card.

  2. 2 Voltage and compressor windings

    Incoming voltage in range (this plate’s line-voltage code). Compressor windings even, no ground. A shorted compressor will kill a new drive. These L-codes do not exist on 24ACC6. If you are looking at a contactor, you are on the wrong outdoor.

    Expect: Balanced windings. No winding to ground. Line voltage stable under load.

  3. 3 Charge and the drive last

    A starved or flooded compressor will overcurrent. Confirm SH/SC and charge weight. Only then condemn the inverter.

    Expect: Charge on the nameplate. Drive code gone after a cool-down and a clean coil.

Workflows

Silent SL28XCV

iComfort calling, outdoor not ramping.

  1. 1 Prove the call and the live code

    iComfort event list. Bus vs drive.

    Expect: Write whatever Signature outdoor inverter — AC only is showing. iComfort last events.

    If fail: No call at the IFC → stat / harness. Do not change gas parts.

  2. 2 Isolate the first failed step in the sequence

    Weigh-in. Not an EL16XC1 SH chart.

    Expect: Protect: HPS / LPS / drive. No defrost.

  3. 3 Confirm with a number, then the next part

    XC21 on the invoice is the two-stage plate (EL18XC1), not this inverter.

    Expect: Charge: Recover and weigh. Nameplate + ounces/ft. Not piston SH. · ABCD: Communicating to the Infinity indoor / 59MN7 family. D is not Y.

    If fail: Stay on this plate. The out-of-range reading is the part.

    If pass: Reading in range → the next step in this workflow is the repair.

Test points

Charge

Recover and weigh. Nameplate + ounces/ft. Not piston SH.

ABCD

Communicating to the Infinity indoor / 59MN7 family. D is not Y.

Drive

Inverter LEDs / last fault. No contactor coil 24 VAC test.

Gotchas

  • XC21 is not this drive. EL18XCV is the Elite inverter.

Related plates

Install this plate

Install Lennox SL28XCV as Signature · variable-capacity inverter AC.

Signature · variable-capacity inverter AC

This plate — not the sister SKU

  • Not XC21 / EL18XC1 two-stage scroll. Not EL18XCV Elite inverter (different drive / rating). Not a furnace E223.
  • XC21 is not this drive. EL18XCV is the Elite inverter.

Control on this outdoor

  • iComfort events + outdoor drive.
  • No dual cap. No defrost.
  • SL25KCV is this variable family, not XC21.

Hardware

  • Drive: Inverter scroll · variable capacity
  • Bus: iComfort communicating
  • Charge: Weigh-in + line-set

First fire

  1. 1iComfort event list. Bus vs drive.
  2. 2Weigh-in. Not an EL16XC1 SH chart.
  3. 3XC21 on the invoice is the two-stage plate (EL18XC1), not this inverter.

Do not on Lennox SL28XCV

  • Not XC21 / EL18XC1 two-stage scroll. Not EL18XCV Elite inverter (different drive / rating). Not a furnace E223.
  • XC21 is not this drive. EL18XCV is the Elite inverter.

Maker literature

FieldBench does not host manufacturer files. Each link opens the maker’s own literature page in a new tab.

  • Lennox residential furnacesLiterature searchEL296V / ML196E / SLP99V / SL280V listing. Wiring and I/O: LennoxPros.Open manufacturer PDF

Warranty and bulletins

Affected models, serial range, symptom, remedy, date. Maker files open on the manufacturer site.

All bulletins

  • Residential limited warranty

    warranty sheet

    Lennox furnace warranty

    Registered EL / ML / SL / SLP furnace warranty · Dealer claims portal

    Open factsOpen manufacturer PDF

  • Dealer portals

    dealer

    Where remaining service letters live

    Current-year service letters not on a public literature page · Maker dealer portal

    Open factsOpen manufacturer PDF