Carrier Infinity 98 / 59MN7 modulating condensing gas furnaces: quick sheet

Covers: Carrier Infinity 59MN7A and 59MN7B (and the 59MN7C product data family) modulating, variable-speed, 4-way multipoise condensing gas furnaces. Size codes in the 59MN7B literature: 060C17, 060C21, 080C17, 080C21, 100C21, 120C24 (three digits = input in kBtu/h; last two digits = cabinet width, 17 = 17-1/2 in, 21 = 21 in, 24 = 24-1/2 in). Works best with an Infinity communicating control, but also runs adaptively with single-stage or two-stage 24 V thermostats. Bryant sells a similar platform; confirm with the label. For Carrier 59TP6/59SC6 see the Performance 96 sheet.

Single sourceBrands: Carrier8 components

The 59MN7 modulates gas input and blower airflow, uses a variable-speed inducer and a communicating modulating gas valve, and reports status with an amber LED on the control (visible through the blower door). Codes are two digits: count the short flashes for the first digit and the long flashes for the second. The board keeps the last 7 codes through power loss and has a built-in component self-test.

Safety first

Never jumper limit, rollout or pressure switches.
Gas valve, manifold pressure and firing-rate adjustment are for a licensed gas technician.
Holding the door switch closed exposes live 115 V parts: keep hands clear.

How it works

With an Infinity control the wall unit sends the firing rate; with a single-stage thermostat the furnace runs an adaptive sequence choosing a modulated rate (DIP SW1-2 can lock it to minimum heat).

Pressure switches (low, medium, high) prove the inducer draft for each firing range; code 32 / 31 / 43 identify which stage did not close.

If a power interruption happens during a heat call, the blower runs 90 seconds after power returns (code 12) before normal operation.

If polarity is reversed the LED flashes rapidly and the furnace will not run.

Components & tests

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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): Condensing gas furnace with PVC vent pipes and metal ductwork in a utility room by Wtshymanski, CC BY-SA 4.0

Diagnostic guides for this appliance

Guide · Furnace

Furnace control boards: last-fault memory, fault recall and power-cycle rules (Carrier/Bryant, ICP, Goodman/Amana, Rheem/Ruud, Trane, Lennox)

Furnace boards show the current state on an LED or a 7-segment display, and many also keep a fault history. Some keep it only until power is removed; one Carrier-family description says stored codes clear on power loss or about 48 hours after the fault. Others have a fault-recall push button or recall terminal that replays recent faults. Read the LED through the door sight glass first; removing the blower door usually opens the door switch and drops power to the board.

7 steps ~15 mineasy

Guide · Furnace

Gas furnace fall inspection: what a handyman or appliance tech checks, and what goes to a licensed gas tech

Manufacturers and ENERGY STAR call for one professional heating check-up a year, ideally in early fall before the rush. The non-gas part of that visit (filter, airflow, condensate, venting condition, thermostat, blower and wiring, a supervised first fire) can be done and documented by a general tech. Anything that touches the gas valve, gas pressure, burner adjustment, combustion analysis or the heat exchanger belongs to a licensed gas/HVAC technician. This guide is inspection-only.

7 steps ~45 minmoderate

Guide · Furnace

Electric furnace or air handler with heat strips: fall pre-season check

Electric resistance heat has no burner or flue, so the fall check is about airflow, connections and proving every heat stage turns on. Measure supply voltage and the current of each element stage against the rating plate, look for heat-damaged wiring at the element terminals and sequencers or relays, and confirm the limits and blower work. Values come from the unit's rating plate and wiring diagram, not from this guide.

6 steps ~45 minadvanced

Other furnaces manuals

Manual · Furnace

Lennox SL280UHV / SL280UHNV 80% two-stage variable-speed gas furnaces: quick sheet

Lennox Dave Lennox Signature Collection SL280UHV (and the later SL280UHNV / SL280UHNVK revisions) 80% AFUE two-stage gas furnaces with a variable-speed blower and a two-stage, variable-speed integrated control with a seven-segment display. Upflow or horizontal (left or right). Model examples printed in Lennox literature: SL280UH070V36A, SL280UH090V36B, SL280UH090V48B, SL280UH110V60C, SL280UH135V60D. Reading the pattern from those examples (not from a Lennox nomenclature table), the three digits after UH are the input in kBtu/h, the two digits after V are the nominal cooling airflow in kBtu/h (36 = 3 ton, 48 = 4 ton, 60 = 5 ton) and the last letter is the cabinet width (A 14-1/2 in, B 17-1/2 in, C 21 in, D 24-1/2 in). Search terms: SL280UHV, SL280UH, SL280UHNV, Lennox 280 two-stage. For the Lennox ML180/EL180 80% and ML196/EL296 condensing furnaces see the separate quick sheets.

7 components5 common failuresLennox

Manual · Furnace

York / Coleman / Luxaire TM9E 95% single-stage condensing gas furnaces: quick sheet

Johnson Controls (York) TM9E 95% AFUE single-stage multi-position condensing furnaces with a 5-speed standard ECM blower, 40-120 kBtu/h input. Model examples from the York technical guide: TM9E040A10MP12, TM9E060B12MP12, TM9E080C16MP12, TM9E100C20MP12, TM9E120D20MP12 (earlier ...MP11 revisions exist). Pattern: TM9E + input (040-120) + cabinet letter (A 14-1/2, B 17-1/2, C 21, D 24-1/2 in) + nominal airflow (10 = 1000, 12 = 1200, 16 = 1600, 20 = 2000 CFM) + MP + revision. Coleman and Luxaire sell Johnson Controls furnaces under their own names; confirm the model on the rating plate. The two-stage TM9V/TM9Y may show additional codes.

6 components4 common failuresYork, Coleman, Luxaire

Manual · Furnace

York / Coleman / Luxaire TM8E and TMLE 80% single-stage ECM gas furnaces: quick sheet

Johnson Controls TM8E (standard) and TMLE (low NOx) 80% single-stage multi-position furnaces with a 5-speed standard ECM blower, 40-130 kBtu/h. Model examples from the technical guide: TM8E040A12MP11, TM8E060A12MP11, TM8E080B12MP11, TM8E100C16MP11, TM8E120C20MP11, TM8E130D20MP11. Pattern: TM8E/TMLE + input + cabinet letter (A 14-1/2, B 17-1/2, C 21, D 24-1/2 in) + nominal airflow (12, 16, 20 = 1200, 1600, 2000 CFM) + MP + revision. Older TG8S and the two-stage TM8V are related families with their own literature.

4 components3 common failuresYork, Coleman, Luxaire