RCS Model TR65 — RS485 Thermostat Installation Manual

Installation manual for the RCS Model TR65 RS485 Thermostat — a two-part thermostat with a Wall Display Unit (WDU) and a separate HVAC Control Unit, designed for RS485 networked control applications.

Important: Do NOT use this product for building freeze protection — install a dedicated mechanical freeze protection device for that purpose.

System Architecture

The TR65 splits into two components: the TS65 Wall Display Unit (WDU), mounted in the traditional thermostat location, and the ZCV1 HVAC Control Unit, typically installed at the HVAC mechanical system (though it can be placed anywhere in the wiring run between the WDU and the HVAC system). A 4-wire cable (thermostat wire or Cat 5) connects the WDU to the Control Unit; a 5-wire minimum thermostat cable connects the Control Unit to the HVAC system.

Wiring Approach

• Retrofit installations: reuse existing thermostat wiring (4 wires required) — install the WDU at the thermostat end, cut the cable at the desired Control Unit location, and splice it in-line.
• New construction: prewire from the thermostat location to the HVAC system with thermostat wire (5-conductor, 18–20ga) or Cat 5 cable.

Before removing the old thermostat: write down the existing wiring connections and label each wire with its terminal marking — wire color codes are NOT standardized beyond simple 5-wire systems, so don't rely on color alone.

Old Thermostat Terminal Reference

Wall Display Unit (WDU) Installation

For new installations, avoid outside walls, drafty locations, direct sunlight, near HVAC vents, and corners/behind doors — these skew temperature sensing.

1. Mark installation hole locations and install screw anchors.
2. Run wiring through the back plate.
3. Install the back plate with the provided screws.
4. Connect wiring to terminals — double-check wiring; mis-wiring can damage the unit.
5. Record the terminal wiring colors for connecting the WDU cable at the HVAC Control Unit end.

WDU to Control Unit wiring: +V/GND/CLK/DAT on the WDU correspond to G/R/Y/W on the ZCV1 Control Unit's "Zone 1" terminal block, respectively. A 4-wire connection is required.

Remote Sensors (on the WDU)

Two remote sensors can attach to the Wall Display Unit — use only RCS 10K Thermistor-style sensors (Model RTS3 or RTS4). Wiring is non-polarized.

• RS1 — replaces the internal sensor entirely
• RS2 — averaged with the internal sensor, or with RS1 if attached

HVAC Control Unit Installation

Install in a protected, convenient indoor location near the HVAC system (equipment closet or garage), mounted vertically on a wall or sturdy structural member. If mounted on the HVAC system itself, avoid hot burner sections or high-vibration areas.

Wall Display Unit connection wire spec: 4-conductor 18/20ga thermostat wire, 22ga twisted pair, or Cat 5 (preferred). Standard thermostat wire color code: Ground=Green, 12VDC=Red, Clock=Yellow, Data=White. Preferred Cat 5 color code: Ground=Brown pair, 12VDC=Blue pair, Clock=Green pair, Data=Orange pair.

Outside temp sensor (Model OS5, optional): 2-conductor 22ga twisted pair or Cat 3/5, non-polarized, wired to the S1 terminal.

RS485 Network Connection

The RS485 port is a 2-wire (D+/D–) plus ground, half-duplex network connection, supporting runs up to 4,000 ft. Three wiring methods are supported:

1. Direct connection to an RS485 host com port
2. Multi-drop (daisy-chained) to other thermostats/devices — a 100-ohm line termination resistor is recommended on the last device if the run exceeds 100 ft
3. Homerun wired to an RCS Star Wiring Hub (Model CS308 or 8AH485), with each HVAC Control Unit homerun-wired to the hub

Wiring note: always wire + to + and – to –, regardless of whether the labels read D+/D-, A/B, or TX/RX.

To connect to a PC or control system: use an RS232-to-RS485 converter (e.g. RCS Model 485PB 5-Port, B&B Electronics 485DB9TB, or USConverters RS485) or a USB-to-RS485 converter (B&B 485USBTB-2W, USConverters US485MIO or USB485CAB).

Power Connection

The HVAC Control Unit requires 24VAC power, sourced either from the HVAC system itself or an external 24VAC 40VA transformer (not supplied). Connect only one power source — do not connect HVAC system power if using an external transformer.

Vent Damper Wiring (Optional)

• RD Series (2-wire): normally closed, power-open/spring-return damper — requires 2-conductor cable
• RDM Series (3-wire): power-open/power-close damper — requires 3-conductor cable

Recommended wire: 18/20ga thermostat wire. Vent damper output is 24VAC, 1A max.

HVAC System Connection

Standard Gas/Electric: RC (24V, blue) → C, RH (24V, red) → R, W1 (white) → W1, W2/CO (orange) → W2, G (green) → G Fan, Y1 (yellow) → Y1 Compressor 1, Y2 (brown) → Y2 Compressor 2. JP1 jumper commons RH and RC for single-transformer systems — cut it for separate-transformer systems (this also switches W1/W2 to RH and G/Y1/Y2 to RC).

Heat Pump: Same RC/RH/G/Y1/Y2 mapping, but W1 becomes Aux Heat and W2/CO becomes the O/B Changeover Valve output. Do not cut JP1 for heat pump systems — leave RH and RC connected. Set the correct Changeover valve operation (O for CO w/Cool, B for CO w/Heat) on DIPSW1 on the control board.

HVAC System Setup — Dipswitch SW1

The TR65 must be configured for the correct HVAC system type via the SW1 dipswitch on the HVAC Control Unit before use.

Any change to SW1 requires power-cycling the HVAC Control Unit. Confirm the configuration on the WDU's Main Menu → Thermostat Info screen.

System Checkout (Bench Test Before Final Install)

1. Set dipswitch DIPSW1 to ALL OFF before power-up.
2. Connect the WDU to the Control Unit with a 3-ft 4-wire cable, then power the Control Unit with a 24VAC transformer.
3. Verify the Status LED flashes and the WDU displays the current temperature (a "CF" display means a Communications Failure — check your wiring).
4. Press the WDU Fan button — the Control Unit's Fan LED and relay should turn on, then off when pressed again.
5. Select Heat mode and raise the setpoint above current temp — the Heat LED and relay should engage (after any MOT delay).
6. Select Cool mode and lower the setpoint below current temp — the Y1 and Fan LEDs/relays should engage (after any MOT delay).
7. Before final installation, set SW1 to the correct configuration for your actual HVAC system type.

Communications Test with a PC

Connect the RS485 port to a PC COM port via an RS232-to-RS485 converter. Using HyperTerminal at 9600 baud, no parity, 8 data bits, 1 stop bit, no flow control (CAPS lock ON — commands are case-sensitive): send A=1 R=1 to request status, A=1 M=H to set Heat mode, or A=1 SPH=78 to set the heating setpoint to 78°.

HVAC System Quick Test

If the TR65 has trouble controlling the HVAC system, verify the HVAC system independently by shorting across its thermostat connection terminals: R-to-G confirms Fan operation, R-to-W confirms Heat, and R-to-Y plus R-to-G together confirm Cool. If any of these fail, the HVAC system itself is not working correctly — call an HVAC professional.