Carrier 25HCS3 Comfort™ Series Heat Pump Wiring Diagrams

For 1 1/2 To 5 Nominal Tons with Puron® Refrigerant

Connection Diagram

This section illustrates the physical wiring connections for the heat pump unit. It shows how the power supply (208/230V) connects to the outdoor unit, and how the outdoor unit connects to the indoor unit and thermostat.

Key Connections Shown:

Power Supply: L1, L2, Equipment Ground (EQUIP GND).
Outdoor Unit Components: Compressor (COMP), Capacitor (CAP), Outdoor Fan Motor (OFM), Crankcase Heater (CH), Start Relay (SR), Start Capacitor (SC), Start Thermistor (ST), various control points (*CHS, *CH, *LPS, *DTS, *HPS).
Control Wiring: Connections to the Circuit Board (CB), Defrost Control (DFT), Reversing Valve (RVS), and other control signals.
Indoor Unit/Thermostat: Connections labeled C, Y, O, W2, R, G, L, W3.

The diagram uses lines to represent wires, with labels indicating the component or terminal they connect to. Specific wire colors (e.g., BLK, BLU, BRN, RED, YEL, WHT, ORN, PNK) are indicated.

Schematic Diagram (Ladder Form)

This diagram provides a logical representation of the electrical control system, similar to a ladder logic diagram. It details how components interact through relays and switches.

Main Circuits Depicted:

Power Circuit: Shows L1 and L2 power feeding contactors (CONT) and components like the compressor and fan motor.
Control Circuit: Illustrates the 24V control signals originating from the thermostat and processed by the Circuit Board (CB) and Defrost Control (DFT).
Defrost Control: Details the defrost relay and circuitry (DR), defrost thermostat (DFT), and its interaction with the system to initiate defrost cycles.
Safety Circuits: Includes connections for High Pressure Switch (*HPS), Low Pressure Switch (*LPS), and Discharge Temperature Switch (*DTS) which can interrupt operation for safety.
Component Control: Shows how the reversing valve solenoid (RVS/RVSR), auxiliary heat relay (AUXR), and compressor are energized or de-energized based on system logic and inputs.

Note on Defrost Control Board: The board includes a five-minute short cycle protector, ensuring a five-minute delay between compressor off/on cycles.

Legend

This section defines the abbreviations used in the wiring diagrams:

FACTORY POWER WIRING: Factory-installed power wiring.
FIELD POWER WIRING: Field-installed power wiring.
FACTORY CONTROL WIRING: Factory-installed control wiring.
FIELD CONTROL WIRING: Field-installed control wiring.
CONDUCTOR ON CIRCUIT BOARD: Wire termination point on the circuit board.
COMPONENT CONNECTION: General connection point for a component.
1/4 INCH QUICK CONNECT TERMINALS: Standard quick-connect terminals.
FIELD SPLICE: Point where field wires are joined.
JUNCTION: A junction point for multiple wires.
PLUG RECEPTACLE: Socket for a plug connection.
AUXR: Auxiliary Heat Relay
CAP: Capacitor (Dual Run)
*CH: Crankcase Heater
*CHS: Crankcase Heater Switch
COMP: Compressor
CTD: Compressor Time Delay
CONT: Contactor
CB: Circuit Board
DFT: Defrost Thermostat
DR: Defrost Relay and Circuitry
*DTS: Discharge Temperature Switch
*HPS: High Pressure Switch
*LPS: Low Pressure Switch
OFM: Outdoor Fan Motor
RVS: Reversing Valve Solenoid
RVSR: Reversing Valve Solenoid Relay
*SC: Start Capacitor
*SR: Start Relay
*ST: Start Thermistor

Note: Components marked with an asterisk (*) may be factory or field installed.

Notes

Compressor and fan motor are furnished with inherent thermal protection.
Wiring must be in accordance with the National Electric Code (N.E.C.) and local codes.
N.E.C. Class 2, 24V circuit; minimum 40 VA required, 60 VA on units installed with LLS.
Use copper conductors only from disconnect to unit.
Must use the thermostat and sub-base as stated in pre-sale literature.
If the indoor section has a transformer with a grounded secondary, connect the grounded side to "C" on the circuit board.
If any of the original wire, as supplied, must be replaced, use the same or equivalent wire.
Check all electrical connections inside the control box for tightness.
Do not attempt to operate the unit until service valves have been opened.
Use conductors suitable for at least 75°C (167°F).

DIP Switch Settings

This section details the selectable options for the time period between defrost cycles using DIP switches on the control board.

Setting	30 MINUTES	60 MINUTES	90 MINUTES	120 MINUTES	QUIET SHFT (DEFAULT)
DIP Switch Position	1 2 3	1 2 3	1 2 3	1 2 3	OFF (DEFAULT)
Field Selectable Options	OR	OR	OR	ON

Speed Up Function:

The "SPEED UP" function is accessed via jumpered test pins. Using a metal object:

Momentarily short pins and release to bypass the compressor off delay.
Short for 5+ seconds and release for forced defrost.
A permanent short will be ignored.

Defrost will terminate normally if the Defrost Thermostat (DFT) is closed. Defrost will terminate in 30 seconds if DFT is open.

Figure Caption

Fig. 1 – Wiring Diagram – Model sizes 1-1/2 – 5 tons, 208/230-1

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