Goodman Furnace 1dL (IdL): Idle, Not an Error

What Goodman's manuals say 1dL means

Every Goodman display manual cited here lists the idle reading among its normal states, and the troubleshooting charts begin with it as normal operation. The spelling varies between IdL, IDL, I dL and 1 d L, but the meaning does not.

The manuals also describe it in their power-up sequences. The *M9C96: "The control will display I d L, idle mode until a call from the thermostat is received." (IOG-2027B p. 39). The *MVC80: "7-segment LED’s display Id L while awaiting call from thermostat." (IOG-2023A p. 28). The *M9S80*U adds what comes first: "Upon power-up of the control board, all Seven segments will be illuminated displaying “8 8 8”. After power-up the displays will show “I d L”, idle, or stand-by mode." (IOG-2031A p. 18)

Why it reads as 1dL

The display font in Goodman's manuals draws the capital I of IdL as a single short vertical bar, the same shape a seven-segment display uses for the digit 1. On the rendered status tables in IOG-2029A (p. 42) and IOG-2027B (p. 44) the code appears as "I dL", and the *M9S80*U wiring-diagram table on p. 32 settles it by printing the first segment as the digit "1".

So 1dL, IdL, IDL and "I d L" are the same idle reading. Two related readings on these displays are also normal: 888, which the *M9S80*U manual describes as "All segments illuminated = control powering up" (p. 19), and on the two-character *MVM96 and *MVM97, "On", which their charts give as "• Normal operation" (IO-406E p. 52).

The other normal status codes on these furnaces

These status tables are the full lists of normal readings for two of the series. A code from these lists means the furnace is reporting a mode, and the same lists for the *M9C96 and *MVC80 are on the 9H page.

If the furnace isn't heating while it shows 1dL

Goodman's description of IdL is a control waiting for a call: "idle mode until a call from the thermostat is received" (IOG-2027B p. 39). A display that stays on 1dL while the house is cold means the control is reporting that it has no call from the thermostat at that moment, rather than a stored fault.

The flash-code *MEC96 has the same state in LED form, "Green: Solid ON" with the description "•Furnace is not receiving a call" (IOG-2011U p. 54). Real faults on the display furnaces appear as their own codes, mostly starting with EE or E1, and the full charts for each series, with how to view stored faults, are on the Goodman furnace codes hub. A limit fault, for example, shows as EE3; its flash-code equivalent has a page of its own.

Two other readings on the same display are normal too: 9H, which is gH, the gas-heat status, and F02, a blower speed number.

Goodman's safety wording

These are gas furnaces even when they are idle. Goodman prints its gas-leak instruction on p. 3 of IOG-2031A and IOG-2027B and p. 2 of IOG-2023A; the wording is below with the carbon monoxide warning.