RCS ZTech ZC4 4-Zone HVAC Controller — Installation & Operation Manual

Installation and operation manual for the RCS/ZTech ZC4 4-Zone HVAC Controller, which lets up to four standard electronic thermostats independently control temperature in up to four zones of a building using a single heating/cooling mechanical system.

Overview

The ZC4 controls temperature by opening/closing motorized dampers (forced air) or valves (hydronic systems) for each zone. It is compatible with Standard HVAC systems (single-stage heat, single-stage cool) and Heat Pump HVAC systems (two-stage heat, single-stage cool), including changeover-with-cooling (O) or changeover-with-heating (B) configurations. All four zones operate independently and can be in any mix of heating or cooling modes; the controller auto-changes over between heating and cooling and gives heat calls priority. Operation is fully automatic — each zone thermostat provides complete control for its zone, effectively acting as its own heating/cooling system.

Short Cycle Protection

The controller enforces a 5-minute delay between successive compressor operations to prevent damage from rapid off-on cycling. This delay resets if power is removed from the controller — useful for testing.

Thermostats

• Use standard thermostats for Gas/Electric HVAC systems and Heat Pump thermostats for Heat Pump HVAC systems.
• Use only electronic thermostats (normal or setback) that are battery operated or use BOTH sides of the 24VAC power from the HVAC system.
• Do not use power-stealing thermostats — these "steal" power from the "W"/Heat connection and will not work.
• Do not use older mechanical thermostats with "anticipator" circuits — they will not function properly.
• Thermostats connect to the zone controllers the same way they'd connect directly to an HVAC system.

HVAC Systems Supported

Forced air gas heating, electric heating, split systems, cooling-only systems, heat pumps, and circulating hot/chilled water systems. Standard systems get one stage of heat and one stage of cooling. Heat Pumps get two stages of heat (Stage 1 = compressor output Y, Stage 2 = heat output W) and one stage of cooling (Stage 1 = compressor Y + changeover valve CO). Changeover with heat or cooling can be selected via dipswitch.

Note for Heat Pump systems: The Emergency Heat (EH) switch on thermostats cannot be used for EH mode. To enable EH function (no compressor output), set EH mode via dipswitch SW1 position 4 on the ZC4 unit itself.

Zone Dampers / Valves

The controller provides independent temperature control by regulating conditioned airflow (dampers) or water flow (valves) using two-position, on/off control.

• Dampers: Normally open, two-position, spring-return, 24VAC, 2-wire motorized dampers (e.g. ZTECH RD series round motorized dampers), drawing 0.5A each. Normally-open design provides fail-safe operation. When a zone calls, all other non-calling zone dampers close. Max rating per zone: 1.0A.
• Valves: For water-based heating, each zone controls a two-position, spring-return, 24VAC, 2-wire motorized valve. Max rating per zone: 1.0A.

Thermal Equalizer Feature (ZTE Version)

Patented feature for two-story, forced-air applications that reduces heat stratification. Heat naturally rises and overheats the upstairs zone during heating cycles, leaving downstairs cooler and calling for more heat. The Thermal Equalizer monitors Zone 1 (must be the "downstairs zone") heat run time, and after a selectable timeout, stops the heat call and recycles overheated upstairs air back down. During an equalizer cycle, the Zone 2 damper (must be the "upstairs zone") closes and the high-speed fan turns on. Zones 3 and 4 are unaffected.

Installation

• Install near the HVAC mechanical system or in a convenient indoor service location (garage, basement, closet, utility room).
• Mount to a wall or structural bracing — mounting directly on the HVAC unit is possible but not recommended due to vibration/heat.
• Use standard 18GA thermostat wiring for both thermostat-to-controller and controller-to-mechanical-system runs.

Power

Requires an external 24VAC power transformer connected to terminal J8. Do not power from the HVAC system — a 4-zone system's damper/valve load can exceed the HVAC system's available 24VAC supply.

Size the transformer for your damper/valve load: calculate max damper/valve current + 0.1A for the controller itself. Example: 3 dampers at 0.5A each + 0.1A controller = 1.6A × 24VAC = 38.4VA → use a 40VA transformer. 6 dampers + 0.1A = 3.1A = 74.4VA → use a 75VA transformer. The controller ships with a 3A fuse; increase it if your damper load calculation requires a larger rating.

Thermostat Wiring

Connect zone thermostats to their respective zone input terminals J1–J4. Both 24VAC Common (C) and 24VAC (R) power are available at these terminals; only 24VAC (R) is required for proper thermostat input, while 24VAC Common (C) is provided for thermostats that need power from the system.

Standard thermostat wiring: 24VAC COM (C), 24VAC (R), FAN (G), HEAT (W), COMP (Y) connect through to the corresponding Zone 1 Input terminals on the controller.

Heat pump thermostat wiring: Same as standard, plus a CHANGE OVER (O) terminal — see changeover terminal note below.

Changeover terminal selection (Heat Pump only): Heat pump systems use a changeover/reversing valve to switch between heating and cooling modes. Two types exist — changeover with Cooling ("O" terminal, most common) and changeover with Heating ("B" terminal). You must know which type your system uses (check existing thermostat wiring on a retrofit, or your HVAC manual), then set dipswitch SW1 position 3 to match.

HVAC System Wiring

The ZC4 connects to the HVAC mechanical system at the normal thermostat terminals on the HVAC unit, via terminal J5.

• Standard heating/cooling with common power supply: Wire R (24VAC/red), G (Fan/green), W (Heat/white), Y (Comp/yellow) straight through from controller to the HVAC indoor unit's thermostat terminals.
• Standard heating/cooling with separate power supplies: Requires an additional external 24VAC relay — wire the relay's R/W to the separate heating system while the main run goes to the indoor unit/outdoor compressor as above.
• Heat pump systems: Wire R, G, W2 (Aux Heat), Y (Comp), and O (Changeover) from the controller to the indoor air handler, which relays Y (Comp) and O (CO Valve) on to the outdoor compressor.

Dipswitch (SW1) Settings

Note: There is a 2-minute minimum Heat Run Time (MHRT). If a heat call ends during this period, no equalizer cycle starts. If the heat call lasts longer than MHRT but less than the selected Heat Run Time, an equalizer cycle starts at the end of the call.

Status LED