Generac Error Code 2780: Charger Missing AC

What code 2780 means

An air-cooled Guardian keeps its starting battery topped up with a charger built into the controller, fed by 120 V on the T1 wire. T1 originates in the transfer switch (behind a fuse on RTS and HomeLink switches) and lands on the customer-connection strip in the generator. Generac's charging-system article explains where that 120 V comes from: from the utility whenever the grid is up — charging continues "even if the controller is OFF and/or the generator's MLCB is OFF" — and, during an outage, from the generator's own output once the switch has transferred, which needs the MLCB ON and the unit running. The charger monitors its own input; when T1 goes dead, the controller lights the yellow LED and posts CHARGER MISSING AC.

Generac's 2780 article (Sep 21, 2026) gives the meaning as: "Code 2780 normally indicates that the controller is not detecting the expected 120 VAC on the T1 battery charging circuit. This may be caused by an issue with the T1 wire or T1 fuse." During an outage, it adds, the warning "may occur if the automatic transfer switch did not transfer to generator power or the generator main line circuit breaker (MLCB) is not set to ON." Generac's starting-issues article says that "'Charger Missing AC' warnings are expected during outages and are not indicative of charger faults."

The version that matters is 2780 with the utility on. Then the battery is slowly discharging with nothing to replace it, and in a few weeks you'll have 2750 Low Battery (below) — or a unit that won't crank when the next outage hits.

Mobile Link messages: 2780 — "The unit is not charging the battery properly. Please contact a dealer." 2770 — "The battery is not charging properly. Please replace the battery or contact a dealer." 2750 — "The battery charge level has fallen below the acceptable level. Please inspect or replace the battery. If necessary, please contact a dealer." On colour, Generac's two owner-facing documents disagree about one of these, and it is worth knowing which you are reading. The published error-code list puts 2750 Low Battery among the red alarms; the Quick Reference Guide in the 10–26 kW owner's manual (A0001846499) lists LOW BATTERY as YELLOW, with a yellow LED lit "in any state" — that is, the unit keeps running — and the owner action being the BATTERY menu. Both are Generac documents and neither is a dealer table, so this page reports the disagreement rather than picking a winner. 2770 and 2780 are yellow warnings in both, and on both the unit keeps running.

One number people search alongside these — 2690 — does not appear in Generac's published error-code list for air-cooled units at all, and no owner-facing definition for it exists. If your panel shows it, there is nothing on this page to apply: call a dealer.

How to clear Generac code 2780

You don't clear 2780 with a key press so much as give the charger its 120 V back: Generac says the code "should clear automatically after the underlying issue is corrected." During an outage, check that the generator's main line circuit breaker is ON. With the utility on, the T1 fuse and wiring are a technician's check. A few Next Generation units show it as a nuisance warning.

What Generac's 2780 article lets an owner do, by situation:

1. During an outage, with the generator running: "Check that the MLCB is set to ON." If the generator runs but the house did not transfer, that is a transfer-switch question — see runs but no power.
2. With utility power on: "A qualified technician can use a multimeter to confirm the voltage received on the T1 wire," and "can inspect the T1 fuse inside the transfer switch." Its warning: "Generac does not recommend end users attempt to modify or service internal generator wiring or attempt to service the transfer switch."
3. On some Next Generation units: "A limited number of Next Generation Air-Cooled Standby generators may display Charger Missing AC code 2780 even when the generator is operating normally and the battery charger is maintaining the battery." The article treats it as a possible nuisance warning only when a qualified technician confirms all four of: "The battery voltage is greater than 12.1 VDC", "The battery charger is maintaining the battery properly", "The T1 wiring is correctly connected", and "The T1 fuse has been inspected and is not blown." Such a unit "should continue to exercise and operate during an outage." If the battery reads below 12.1 VDC, the article says to contact a dealer.

The owner's manuals give CHARGER MISSING AC one solution: "Contact an IASD." (Guardian A0001846499 Rev. C, p. 35; Next Generation A0004332577 Rev. C, p. 38). For 2750, 2760 and 2770 the yellow-warning clear applies once the cause is fixed; the key presses are under clearing a yellow warning. Generac's 2770 article adds: "If the warning message does not clear in Mobile Link, run the generator temporarily in Manual mode for at least one minute to change the generator's status, then set it to AUTO."

Tracing a missing T1 feed

Battery and fuse numbers for charger codes

The T1 fuse is part of the transfer switch, and its rating and holder differ between RTS and HomeLink models; no part number is listed because none could be confirmed with fitment. The battery charger is integrated into the controller on Evolution units and is not sold as an owner-replaceable part.

When a charger warning needs a dealer

The four battery and charger codes compared

The codes on this page describe the same circuit from different angles: 2780 — no AC into the charger; 2770 — the battery still under 12.5 V at the end of an 18-hour charge; 2750 — battery voltage low right now; 2760 — named by Generac among the same family, without a published owner-facing definition. A unit with no code that won't crank is covered in Generac won't start. What the yellow light means on each controller: Generac lights and alarms. A miswired T1 at installation can also show up as a 2098/2099 wiring error.