Aprilaire Model 8870 Communicating Thermostat System — Whole-System Installation Manual

Installation manual for the Aprilaire Model 8870 Communicating Thermostat System, covering the full 14-step process for wiring, mounting, and checking out a multi-zone RS-485 communicating thermostat network with Model 8818 Distribution Panels and a Model 8811 Protocol Adapter.

Overview

This manual guides installers through installing, wiring, and checking out a complete Aprilaire Model 8870 Communicating Thermostat System. (Instructions for the Aprilaire 8840 Series communicating thermostat system are covered in a separate document, Part No. 10004345.) A full command set for custom software integration is available as DP 10005756 from Research Products Corporation (888-782-8638).

Warning: 120 volts may cause serious injury from electrical shock — disconnect electrical power to the HVAC system before starting installation (this system itself is low-voltage). Improper installation may cause serious injury; the system must be installed by a qualified contractor per NEC standards and applicable local/state codes.

System Components

• Model 8870 Communicating Thermostat — one per zone or single-zone HVAC system. RS-422 communicating thermostat controls single- or multi-stage heat/cool or heat pump HVAC systems. Field-configurable via menu-driven setup. Network communication is non-isolated, full-duplex RS-485 (RS-422): 'A' terminals are receive, 'B' terminals are transmit (host/computer reference). Baud rate selectable 9600/19200. Up to 64 uniquely addressed thermostats per network.
• Model 8818 Distribution Panel — one per 8 thermostats. A switch-controlled communication bus wired to up to 8 thermostats; each thermostat station has individual power and communication on/off switches for easy installation and troubleshooting.
• Model 8811 Protocol Adapter — one per 32 thermostats. Converts RS-485 communication signal to RS-232, readable by a host computer.
• Model 8061 / 8062 Support Modules — up to 4 per thermostat, each supporting 2 sensors. Model 8061 has one onboard + one offboard temperature sensor slot; Model 8062 has one onboard temperature and one onboard humidity sensor. Sensors can be configured as control (replaces thermostat sensor) or monitor (read-only).
• 4-8 conductor thermostat cable (18-20 gauge), depending on equipment stages.
• Category 5 communication wire (4-pair twisted cable) for all communication wiring.
• One 24VAC ungrounded transformer per Distribution Panel (Model 8027, or 8029 for California).
• RS-232 or RS-485-based automation system, such as the Aprilaire Model 8825 System Controller.

Tools needed: small flat-head screwdriver (1/8" tip) for terminal screws, medium flat/phillips screwdriver for component mounting, volt/ohm meter, computer with RS-232 com port and terminal emulator (e.g. HyperTerminal), wire strippers, small level.

Installation Steps (14 Total)

Step 1 — Get All the Components You Will Need

Gather all components and tools listed above before beginning.

Step 2 — Disconnect Power to All HVAC Equipment and/or Zone Control Panels

If thermostats are wired to a zone control panel, disconnect the input terminals supplying power to thermostats and dampers. If wired directly to HVAC equipment, shut off power at the equipment disconnect switch, or remove the fuse / shut off the circuit breaker if no disconnect is available. Caution: Failure to disconnect power could damage HVAC equipment or thermostats — leave power off until all connections are made and checked.

Step 3 — Run the Required Wires

1. Run thermostat cable (4-8 conductor, per equipment type/stages) from each thermostat to the HVAC system or zone control panel — run one more wire than a mechanical thermostat would need. If using remote temperature/humidity support modules, run a separate Cat-5 cable from thermostat to support module.
2. Label each thermostat's cable location with tape as you go, at the HVAC/zone control system.
3. Run Category-5, 4-pair twisted (8-conductor) cable from each thermostat to the Distribution Panel; label locations at the panel.
4. Run Category-5 wire from the Distribution Panel to the Protocol Adapter (and between Distribution Panels if multiple are used).
5. Run two-conductor thermostat cable from the Model 8027/8029 Transformer to the Distribution Panel (Cat-5 can substitute, using one pair per terminal).

Maximum Wiring Distances

Step 4 — Locate and Mount the Automation System Components

• Locate thermostats/sensors per their own installation instructions. Set the thermostat's four configuration dip switches and sensors' six configuration dip switches per equipment requirements (see individual product manuals).
• Complete a Network Interconnection Worksheet documenting the location/name of each thermostat and how communication components connect — this saves significant time during software setup.
• Mount zone control panel(s) per their own installation instructions, if the system is zoned.
• Mount the Distribution Panel indoors in an accessible location (closet/utility room) with adequate workspace — it has wire access holes on top, bottom, sides, and back.
• Place the Protocol Adapter within 3 feet of the host computer or automation system's RS-232 port.
• Locate the Model 8027/8029 plug-in transformer near the Distribution Panel. When using multiple panels/transformers, keep polarity consistent (R to R, C to C) across all panels — critical for stable communications even though power is AC.

Step 5 — Connect the Control Wires to the HVAC/Zone System and Thermostats

Should be performed by a qualified HVAC technician. Ensure HVAC system power is off before wiring — do not turn on power yet. Use 18-20 gauge thermostat cable; the manual provides reference wiring schematics for typical multi-stage furnace/A/C systems (terminals Y1/Y2, W1/W2, G, C, R) and typical heat pump systems (terminals Y1/Y2, O/B reversing valve, W1/W2 aux heat, G, C, R, L). Refer to the thermostat's own installation sheet for internal schematic and full wiring details.

Step 6 — Connect the Communication and Power Wires to the Distribution Panel and Thermostat

1. Make sure all switches on the Distribution Panel are OFF.
2. Connect communication wires per the standard wire-color scheme: B+/B- = Transmit (from automation system), A+/A- = Receive (from thermostats), REF = ground reference, R = thermostat voltage (hot), C = thermostat voltage (common).
3. Connect the REF terminal of each thermostat to the Distribution Panel REF terminals only if: (a) more than one transformer powers thermostats in the network, or (b) the installation environment has excessive electromagnetic interference (fluorescent lights, motors, industrial/office settings).

Step 7 — Connect Multiple Distribution Panels

Ensure all Distribution Panel switches are OFF. If more than one Distribution Panel is used, daisy-chain the communication lines together using consistent wire colors. If necessary (per Step 6 REF guidance), connect the REF terminal for each thermostat to its panel's REF terminal, and connect REF terminals between panels.

Step 8 — Connect Protocol Adapter to the Distribution Panel and Host Computer or Automation System

1. Ensure all Distribution Panel switches are OFF.
2. Use Category-5 wire to connect the Distribution Panel's main communication terminals to the Protocol Adapter's Breakout Adapter.
3. Connect the provided 3 ft. RS-232 cable from the Protocol Adapter to the computer/automation system (DB9-to-DB25 adapters available at retail if needed for 25-pin serial ports).
4. Power up the Protocol Adapter with the provided plug-in transformer — the "Power" LED should light.

Step 9 — Provide Power to the Distribution Panel

1. Ensure all Distribution Panel switches are OFF.
2. Use 2-wire thermostat cable to connect the Model 8027/8029 transformer's load terminals to the Distribution Panel's 24VAC terminals — R to R, C to C.
3. Plug in the transformer.
4. No LEDs on the Distribution Panel should be lit at this point.

Step 10 — Turn On Power to All HVAC Equipment and to the Thermostats

1. Turn on power to the HVAC and/or zone control systems.
2. Verify no LEDs are lit on the Distribution Panel. If any LED is on, immediately unplug the transformer — this usually means the HVAC system transformer is powering the thermostat improperly (check for a stray jumper between RH/RC and R at the thermostat; only the Cat-5 cable should supply the thermostat's R and C terminals).
3. Turn on the main power switch, then the power switch for one thermostat at a time. The green LED next to the switch should light and the thermostat display should power up. Do not turn on other switches yet.

Step 11 — Check-Out HVAC System Operation

Use the thermostat's own buttons to verify it controls the equipment, following the checkout procedure in the thermostat's installation instructions. This confirms equipment operation only; communication system checkout follows in later steps.

Step 12 — Address the Thermostats and Set Highest Address

These steps must be done at each thermostat for communication to work properly.

1. Press Mode and Enter simultaneously to enter the Thermostat Set Up Menu.
2. Scroll down to "Communications Set Up" and press Enter.
3. Select "Set Thermostat ADDRESS" and press Enter.
4. Set a unique address between 1 and 64 using Scroll Up/Down — start at 1 and increment by 1 without skipping (speeds communications). Write the address down on the Network Interconnection Worksheet. (For Model 8840 thermostats mixed on the network, see the Appendix 1 addressing rules below.)
5. Press Enter to store the address.
6. Set "Number of Stats On Network" to the highest address that will exist on the network — this value must match at every thermostat.
7. Set the baud rate (default 9600; optionally 19200) and press Enter.
8. Exit the Communications Set Up sub-menu, then exit the main menu — the thermostat resets and returns to normal operation.

Step 13 — Setup Computer for Communication System Checkout

Connect the Protocol Adapter's RS-232 output to a Windows PC and open HyperTerminal (or add it via Windows Setup if not present). Create a new connection, select the COM port the Protocol Adapter uses, and configure connection properties: 9600 bps (or 19200 if thermostats use that baud rate), 8 data bits, no parity, 1 stop bit, no flow control. Under terminal settings: Emulation = Auto Detect, Telnet terminal = ANSI, Backscroll = 500 lines. Under ASCII setup, enable: echo typed characters locally, append line feeds to incoming line ends, wrap lines exceeding terminal width. Verify the connection by typing a character and confirming the Protocol Adapter's "RXD" LED flashes.

Step 14 — Check-Out Communications to the Thermostat Network

1. Type SN? and press Enter — expect no response since no communication switches are on yet.
2. At the Distribution Panel, turn on the communication switches for thermostat address #1.
3. Type SN? again — the computer should respond SN1, confirming thermostat #1 is communicating. If not, verify the address and switch settings.
4. Type SN ID? — expect a response like SN1 MODEL# 8870 VER: x.xxx - RPC 2006. An incorrect/garbled response indicates a communication signal problem — check terminal connections, wire condition, and consider connecting the REF terminals if not already done.
5. Turn off switches for address #1, turn on address #2, and repeat verification for every thermostat, one address at a time.
6. Once all addresses verify individually, turn on all communication switches together and re-run SN ID? — all thermostats should respond, with response count matching your total thermostat count.
7. Once verified, use your automation/software package to test all thermostat functions, or continue testing via HyperTerminal using the Aprilaire Command Set (see below).

Appendix 1 — Mixing Model 8870 with 8840 Series Thermostats

If adding a Model 8870 to a system already using 8840 series thermostats (8844, 8846, 8847, 8848), two special requirements apply:

• Separate power supply required: Model 8870 and 8840 series thermostats cannot share a power supply. If using a Model 8800-8808 Communication Panel, wire per the manufacturer's schematic for this configuration. If using a Model 8818 Distribution Panel, the 8840 series thermostat must use an 8809 Sub-base to connect its RS-485 communication directly to the Distribution Panel.
• Addressing order: Model 8870 thermostat(s) must either be addressed first on the network, or have one address skipped between them and 8840 series units. Example: adding one 8870 to an existing 4-thermostat 8840 series network — address the 8870 as #1 (renumbering the existing #1 to #5), or simply add the 8870 as address #6. Set "Number of Stats On Network" to 32 and baud rate to 9600 in this mixed configuration.

Note: The Model 8870 has an expanded command set versus the 8840 series — refer to DP 10004345 for the 8840 series command set.

Appendix 2 — Aprilaire Command Set (Summary)

A full command reference (DP 10005756) is available from Research Products Corporation for custom software integration. Command syntax: SN# [Command] [? or =] [Value (with = only)] Enter.

• All commands begin with SN followed immediately by the thermostat address (1-64, or a leading zero for single digits, e.g. "01").
• Omitting the address, or using 0, makes the command global — all connected thermostats respond (exception: SN? or SN0? makes every thermostat return its own address).
• Upper or lower case letters are accepted; invalid characters immediately invalidate the command (backspace/delete are not usable when typing commands directly).
• Responses are sent in upper-case ASCII, using the same syntax as commands but with no separating spaces. Unrecognized commands produce no response (there is no error message).
• Unless marked "Read Only" or "Write Only," all commands are Read and Write. Inquiries (all commands except BLTON) use the syntax SN [address, blank, or 0 for global] [Command]? to read the current value.

Manufacturer

Research Products Corporation (Aprilaire), 1-888-782-8638. © 2008 Research Products Corporation.