Trane / American Standard TUD and TDD (incl. TUD2/TDD2) 80% gas furnaces, older generation: quick sheet

Covers: Older Trane and American Standard 80% non-condensing furnaces with model prefixes TUD/TDD (upflow/downflow), including two-stage *UD2 and *DD2 models such as TUD2A040A9242A, TUD2B060A9362A, TUD2B080A9482A, TUD2C100A9482A, TUD2D120A9602A and TDD2B080A9362A (the first letter * is T for Trane or A for American Standard). Many of these are still in service and many have had their original board replaced. Trane's replacement kit 15943 swaps original White-Rodgers 50M61-495-05 / -06 controls (Trane CNT03077 / CNT05122) for a new silicon nitride (SiNi) control and igniter, and the new board uses a different flash-code table. For current S8X1/S8X2 furnaces see the separate sheet.

Single sourceBrands: Trane, American Standard4 components

The TUD/TDD family uses an induced-draft burner, a hot surface igniter and an integrated furnace control with LED flash codes. The key field fact is that code meanings depend on which control is installed: the original board and the SiNi replacement kit board do not share the same numbering. Always read the code legend on the blower door and check whether a replacement kit label has been added.

Safety first

Gas valve and manifold work, rollout causes and venting go to a licensed gas technician.
Codes 1 and 10 (flame or gas flow without a call) mean shut off gas and refer.

How it works

Heat call: inducer, pressure switch proof, igniter warm-up, gas valve, flame proof, then the main blower after about 45 seconds (as described in the kit's checkout sequence).

TUD2/TDD2 models use a two-stage gas valve and two-speed inducer with a second pressure-switch stage.

The replacement IFC is polarity-sensitive: the hot leg of 115 VAC must be on the black field lead.

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