Advent Air Air Conditioner: “E4”
warning RV air conditioner error codes
What it means
On the Advent ACTH12 thermostat, E4 indicates a communication error between the thermostat (T-Stat) and the relay/control kit, so the two are not exchanging signals correctly.
Most likely causes
- Loose, dirty, or damaged wiring between the thermostat and the relay kit most likely
- Moisture or dust on the connection points in the air distribution box common
- Failed relay kit or failed thermostat less common
Safe checks you can do yourself
- With power off, open the air distribution box and inspect all wiring for damage or loose/incorrect connections.
- Verify the thermostat wires match the relay kit terminals (e.g., A, B, COM, 12V) per the install diagram.
- Clean any dust or moisture from the connectors.
How to reset / clear E4
- With the thermostat in Off mode, press and hold both the Mode and Fan buttons at the same time.
- While still holding them, press the Power button, then release all three buttons.
- Power-cycle the unit at the breaker if the code remains.
When to call a technician
If wiring and connections are confirmed good and E4 still appears, the relay kit or thermostat is likely defective and should be replaced.
Applies to
Advent Air ACTH12 thermostat · Advent Air ducted rooftop AC systems using the ACTH12 / ACRG relay kit
FAQ
What does Advent Air Air Conditioner code "E4" mean?
On the Advent ACTH12 thermostat, E4 indicates a communication error between the thermostat (T-Stat) and the relay/control kit, so the two are not exchanging signals correctly.
How do I reset Advent Air Air Conditioner E4?
With the thermostat in Off mode, press and hold both the Mode and Fan buttons at the same time. While still holding them, press the Power button, then release all three buttons. Power-cycle the unit at the breaker if the code remains.
What is the most common cause of E4 on a Advent Air Air Conditioner?
The most likely cause is loose, dirty, or damaged wiring between the thermostat and the relay kit.
Related · Advent Air air conditioner
Sources
- Advent ACTH12 Operating Instructions (full text) — ACTH12 error code table: E4 Check wire connections at T-Stat and relay kit (Internet Archive / Manualzilla)
- Advent Air Troubleshooting Guide — Communication Defect with T-Stat and Relay Kit (RV Upgrade Store)
Note: Advent code numbering differs from Houghton/RecPro. Some etrailer/JustAnswer field reports describe the communication fault as E5 rather than E4; the ACTH12 manual table assigns the relay-communication fault to E4.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.