RCS ZTech ZC2S 2-Zone HVAC Control Unit — Installation & Operation Manual

Installation and operation manual for the RCS ZTech Model ZC2S 2-Zone HVAC Control Unit, which lets two standard electronic thermostats independently control a single one-stage heat / one-stage cool HVAC system via motorized zone dampers, including the patented Thermal Equalizer feature.

Overview

The ZC2S allows 2 standard electronic thermostats to connect to a single heating and cooling HVAC mechanical system, providing two independent zones of temperature control by regulating the mechanical system and motorized dampers in each zone. It works with any residential-style standard gas or electric heating HVAC system up to 5-ton capacity, supporting one stage of heating and one stage of cooling. Zones are fully independent (either can run heat or cool), with auto-changeover between modes and heating calls given priority. Operation is fully automatic and transparent — each zone's thermostat provides complete, independent control for its zone, as if it had its own separate HVAC system.

Compatible Thermostats

Works with most electronic thermostats (Honeywell, White Rodgers, Lux). Use only thermostats that are either battery-operated or use both sides of the 24VAC power (have R and C terminals).

DO NOT use power-stealing thermostats — these steal power from the "W" (heat) connection and will not work with the ZC2S. Older mechanical thermostats using "anticipator" circuits are also not recommended, as they will not function properly. Thermostats connect to the zone control unit terminals the same way they would connect directly to the HVAC system.

Zone Dampers

The ZC2S regulates conditioned airflow to each zone using two-position (on/off) motorized dampers. Compatible with normally-open, two-position, spring-return, 24VAC, 2-wire motorized dampers such as the RCS RD Series round motorized dampers (0.5A draw each). Normally-open dampers provide fail-safe operation, ensuring conditioned air is available even if a damper motor fails — when Zone 1 calls for heat/cool, the Zone 2 damper closes. Maximum rated current for all dampers combined is 1 Amp (typically 2 dampers).

HVAC System Compatibility

Designed for most standard gas/electric residential heating and cooling systems, providing these outputs:

• One stage of heating: W output
• One stage of cooling: Y output
• Fan: G output (selectable for gas systems with no fan on heat calls, or electric systems requiring fan with heat calls)

The controller connects to the HVAC system at its standard thermostat connections, functioning just like a thermostat. Consult your HVAC system's thermostat wiring diagram to verify compatibility.

Thermal Equalizer Feature

A patented feature for two-story, forced-air applications that reduces heat stratification. During heating cycles, heat naturally rises and the upstairs zone tends to overheat, leaving the downstairs zone cooler and still calling for heat. The Thermal Equalizer monitors Zone 1 (which must be the downstairs zone) for heat run time; after a selectable timeout, it stops the heat call and recycles the overheated upstairs air back down to the downstairs zone via the blower. During an equalizer cycle, the Zone 2 (upstairs) damper closes and the high-speed fan turns on. Net effect: more comfortable upstairs temperature and energy-saving reuse of excess heat downstairs.

Short Cycle Protection

The ZC2S enforces a 5-minute delay between successive compressor operations to prevent damage from rapid off-on cycling. This delay is normal and should be expected when troubleshooting. To reset the 5-minute delay for testing, remove power from the controller. (Most thermostats also have their own built-in short-cycle protection delays.)

Status LED

If the Status LED is not flashing at all, check power and the fuse.

Installation

Install the controller near the HVAC mechanical system or in a convenient indoor service location (garage, basement, closet, utility room). Mount to the wall or structural bracing — mounting directly on the HVAC unit is possible but not recommended due to potential vibration and heat exposure.

Wiring

• Thermostats: Use standard 18 AWG thermostat wire to connect thermostats to the controller and the controller to the mechanical system.
• Dampers: Zone damper outputs provide 24VAC at 1 Amp maximum; use 18 AWG thermostat wire.
• Power: The ZC2S is powered directly from the HVAC system's 24VAC R and C (common) terminals — no external transformer is required. Total damper draw must stay under 1 Amp per zone.
• Fuse: Supplied with a 2AG-style 2 Amp fuse.

Thermostat Wiring

Connect zone thermostats to their respective zone input terminals, J1 & J2. Both 24VAC Common (C) and 24VAC (R) power are available at these terminals. Only the 24VAC (R) terminal is strictly required for thermostat input; the 24VAC Common (C) is provided for thermostats that need power from the system. Each zone's thermostat terminals (24V C, 24V R, FAN G, HEAT W, COMP Y) wire directly to the corresponding ZC2S zone input terminals.

HVAC System Wiring

The ZC2S connects to the HVAC mechanical system at its normal thermostat connections. Standard color-coded wiring: R (24VAC, red) to 24VAC R, G (fan, green) to FAN G, W (heat, white) to HEAT W, Y (compressor, yellow) to COMP Y, plus 24VAC common (C).

Control Unit Setup — Dipswitch Settings (SW1)

Note: There is a 2-minute Minimum Heat Run Time (MHRT). If a Zone 1 heat call ends before the MHRT elapses, no equalizer cycle is triggered. If the heat call lasts longer than the MHRT but less than the set Heat Run Time, an equalizer cycle starts when the call ends. This determines how long a Zone 1 heat call may run before it is interrupted by an equalizer cycle.

Manufacturer

RCS, Model ZC2S, PN: 001-00240, Rev E. Document DCN 141-00240-02.