AprilAire 8840 — Wi-Fi Automation IAQ Thermostat Safety & Installation Instructions

Safety and installation instructions for the AprilAire Model 8840 Wi-Fi Automation IAQ Thermostat — a two-piece thermostat system with a separate equipment control module supporting heat/cool and heat pump systems plus full indoor air quality (humidification, dehumidification, ventilation, air cleaning) control.

Overview

The 8840 system consists of a wall-mounted thermostat and a separate equipment control module. The thermostat powers from the equipment control module (24VAC), which maintains clock memory for 24 hours on power loss and saves settings through a memory backup. The system connects to Wi-Fi either directly at the thermostat or via a browser on a connected device, and can pair with an automation system or an Aprilaire cloud account.

Installation Locations

Thermostat

• Mount: Interior wall, frequently occupied space, ~5 ft. above floor, at least 18" from an outside wall. Can mount to a vertical junction box.
• Avoid: Behind doors, corners/dead air spaces, direct sunlight, near heat-emitting fixtures/appliances, outside/unconditioned walls, supply register airflow, stairwells, near outside doors, or walls with concealed pipes/ductwork.

Equipment Control Module

• Operating range 32°F to 158°F (0° to 70°C). Avoid foundation walls or mounting directly on HVAC equipment/ductwork (moisture condensation risk).
• Static discharge note: Installer must touch a grounded metal object before handling the module.
• Six mounting holes (corners + top/bottom center); mount with 2–4 #8 screws. Wires route through top, bottom, sides, or back; nylon wire ties secure wiring at 10 points.

Thermostat Mounting Steps

1. Remove the rear mounting plate from the thermostat.
2. Pull wires through the opening on the rear mounting plate.
3. Position and level the mounting plate on the wall; mark hole locations.
4. Drill 1/4" holes and insert supplied anchors (drywall only).
5. Place mounting plate over anchors, insert and tighten screws.
6. Seal wire entry holes to prevent drafts from affecting temperature readings.

Wiring

Wire spec: 18–24 gauge thermostat wire. Always ensure power is off at the HVAC equipment before wiring; loosen screw terminals, insert stripped wire, re-tighten; push excess wire back into the wall opening and plug it to prevent drafts.

Thermostat-to-Module Terminals

• 1, 2, 3 — Connections to terminals 1/2/3 at the equipment control module.
• A & B — Model 8081/8082 support module communication (optional).
• T1 & T2 — Remote temperature sensor (optional).

Equipment Control Module Terminals

• C — 24VAC common   R — 24VAC   RC — 24VAC cooling   RH — 24VAC heating
• W / W2 / W3(B) — 1st/2nd/3rd stage heat (conventional) or auxiliary/reversing valve (heat pump)
• Y / Y2 / Y3(O) — 1st/2nd/3rd stage cooling (conventional) or compressor stages/reversing valve (heat pump)
• G — Fan   L — System fault indicator (heat pump only, optional)   CEQ — 24VAC common from heat pump for fault indicator (optional)
• HUM — Humidifier   DHno/DHcom/DHnc — Dehumidifier control (normally open/closed)   VENT — Ventilation   EAC — Electronic Air Cleaner
• RAT — Return air temperature sensor (optional)   LAT — Leaving air temperature sensor (optional)   ODT — Outdoor temperature sensor (included)

Optional Sensors

• Remote temperature sensor (8051 flush / 8053 surface mount): wire to T1/T2, enable in installer setup; mount interior wall, ~5 ft. above floor, ≥18" from outside wall, using <300 ft. of wire.
• Support modules (up to 4, Model 8081/8082): wired with CAT-5 cable, total run for all modules ≤1000 ft. Terminals: RC, C, RSB, RSA, T1–T4.
• Outdoor temperature sensor (8052, included): mount on north side out of direct sun, above snow line, ≥3 ft. from exhaust vents/condensing lines, <300 ft. of wire, not routed along 120VAC lines. Enables heat pump balance points and IAQ humidity/ventilation lockouts. A wireless alternative (Model 8056) is available where wiring is impractical.
• Return air temperature sensor (8052): mounted in the return trunk; if thermostat connection is lost, the module uses this sensor to hold temperature between 40°F and 100°F.
• Leaving air temperature sensor (8052): mounted in the supply trunk after the heat exchanger and cooling coils, for diagnostic display during installer test only — do not mount in direct line-of-sight of the heat exchanger, cooling coils, or UV lights.

HVAC Wiring Diagram Reference

The manual includes wiring diagrams for: conventional heat/cool with a single transformer (jumper installed) or two transformers (jumper removed), and heat pump systems with a single transformer (jumper installed) or two transformers (jumper removed). See the original PDF for full diagrams (terminal labels: HC/HP, W/W2/W3, Y/Y2/Y3, G, L, CEQ).

Indoor Air Quality wiring diagrams cover configurations using separate transformers vs. a single shared transformer for the humidifier, dehumidifier (normally closed damper), ventilation, and electronic air cleaner (via pilot relay for 120VAC). All IAQ outputs are 24VAC dry contact — refer to each accessory's own installation instructions for details.

Power & Reset

The equipment control module runs on 24VAC and powers the thermostat. On power loss, the thermostat clock is maintained for 24 hours via memory backup. A factory reset is available under Installer Menu > Installer Tools.

Installer Setup Wizard

On first power-up (or after a factory reset), the thermostat enters the Installer Setup Wizard, covering all installer settings. Re-access anytime via Menu > press and hold Contractor Info for 10 seconds. The wizard first checks for a USB drive with exported installer setup files (Import USB Settings) — insert a USB drive to import, or press Skip to proceed manually. Setup files can be created via Installer Menu > Installer Tools > Export Setup.

Key Installer System Settings

Default values shown in bold below.

General

• Connection Type: Automation System / Aprilaire Cloud
• Installer Temperature Scale: Fahrenheit / Celsius
• Contractor Information Input: company, phone, email, web

Thermostat / HVAC

• Equipment Type: Heat/Cool / Heat Pump
• Control Setup: Heat & Cool / Heat Only / Cool Only
• Heat Pump Auxiliary Type (heat pump mode): Gas/Oil Heat / Electric Heat
• Number of Compressor Stages (heat pump): One / Two
• Number of Auxiliary Heat Stages (heat pump): One / Two
• Number of Stages of Heat / Cool (heat/cool mode): One / Two / Three
• Remote / Return / Outdoor Temp Sensor Installed: No / Yes (with fallback/average variants)
• Schedule: Enabled / Disabled
• Progressive Recovery: Enabled / Disabled
• Away Button / Heat Blast Button: No / Yes (Heat Blast offset options: 3°F/4°F/5°F, default 3°F)
• Extended Fan – Heat/Cool: Disabled / Enabled
• Auto Changeover: Disabled / Enabled, deadband default 3°F (1.5°C), min. time between calls default 4 minutes
• Equipment Minimum On Time: 2 minutes (1–5)   Heating Minimum Off Time: 2 minutes   Compressor Minimum Off Time: 5 minutes
• Outdoor Temp High/Low Balance Points (heat pump w/ ODT): High default 65°F (0–80°F), Low default 20°F (0–60°F)
• Stage Rate Factor: 2 (1=rapid/comfort staging, 5=slow/economy staging)
• First/Second/Third/Fourth Stage Differential: 1°F each (1–9°F range)
• Service HVAC Reminder: Disabled / Enabled, recurrence default 12 months

Indoor Air Quality

• Humidifier Installed: No / Yes. Mode: Automatic (uses outdoor sensor) / Manual. Allowed Operation: Heat Only / Heat or Fan / Forces Fan. Humidity Deadband default 10% (10–20%). Water panel change reminder options: Off / 300h / 600h / seasonal.
• Dehumidifier Type Installed: None / Whole Home / Air Conditioner. Disable During Cooling default Yes. Overcooling limit default 1°F (1–3°F). Vacation hold low temp limit default 75°F (70–85°F).
• Air Cleaner Installed: No / Yes. Reminder recurrence default 12 months.
• Fresh Air (Ventilation) Installed: No / Yes. Setup Type: Timed / ASHRAE (calculated from bedrooms, occupants, home size, CFM delivered). Fresh Air Time default 30 min/hr (5–55). Indoor RH high limit default 60% (50–70%, Timed mode only). Outdoor temp low/high lockouts default 10°F / 100°F.

Installer System Test

Accessed from the Installer Menu — all configured equipment outputs can be manually turned on/off for testing, with minimum on/off times not enforced in this mode.

Wi-Fi Setup

1. Confirm the thermostat is in Wi-Fi Connection Mode (radio bars strobing by default).
2. Via thermostat: Menu > Wi-Fi Settings > Advanced > Connect without App, select a network, enter password, press Done.
3. Via browser: connect a computer/mobile device to the thermostat's own network (named APRILAIRE8840 + unique ID from the MAC address), browse to http://192.168.1.99/index.html, select the target network and enter its credentials, then confirm connection (radio bars reflect signal strength).
4. If not using a home automation system, register instead to an Aprilaire account per the Wi-Fi Thermostat App User Guide at my.aprilaire.com.

Thermostat Features

• Remote access/control over Wi-Fi; indoor air quality control (humidification, dehumidification, Event-Based™ air cleaning, ventilation with temp/humidity limits)
• Displays room temperature, humidity, setpoints, and optional outdoor temperature
• Air filter, humidifier, dehumidifier, and HVAC service reminders
• Programmable fan control with circulation mode; touch override of schedule anytime
• Heat Blast® raises room temperature 3–5°F; one-touch Away mode
• Optional wireless outdoor temperature sensor support; progressive recovery; built-in compressor protection
• Large adjustable-backlight touchscreen; 7-day programmability; system test mode

Equipment Control Module LED Indicators

• Power/Status: solid during normal operation; flashes when thermostat connection is lost or during power-up pairing.
• Individual LEDs for Heating, Cooling, Fan, Humidifier, Dehumidifier, Ventilation, and Air Cleaning — lit when the respective output is active.

Troubleshooting

Specifications

Manufacturer

AprilAire (Research Products Corporation), P.O. Box 1467, Madison, WI 53701-1467. Phone: 800-334-6011. Fax: 608-257-4357. www.aprilairepartners.com. Full owner's manual available at my.aprilaire.com.