Relays

HVAC relays are electromechanical switching devices that use a low-voltage control signal, typically 24V AC from the thermostat circuit, to open or close higher-voltage power contacts that energize loads such as compressors, condenser fan motors, blower motors, heat strips, and zone valves. The HVAC relay category on SupplyHouse spans OEM relays for Carrier, Lennox, Nordyne, and other major equipment brands, as well as universal switching relays, general-purpose SPST and DPDT switching relays, contactors, and time-delay relays used across residential and commercial HVAC applications. Carrier relays on SupplyHouse include time delay relays, coil power relays, compressor lockout sensing relays, relay boards, fan relays, electric heat relays, and start relays for the full Carrier equipment lineup. For service technicians, confirming the relay coil voltage, contact rating, and pole configuration before ordering is the first step in selecting a compatible replacement.

Carrier OEM Relays

Carrier OEM relays are factory-replacement switching components for Carrier HVAC equipment, covering time delay relays, fan relays, electric heat relays, compressor lockout sensing relays, and relay boards for Carrier furnaces, air handlers, heat pumps, and condensing units. Carrier relay types include SPST, DPST, and multi-pole configurations with coil voltages specific to the Carrier equipment model. The Carrier relay category on SupplyHouse includes relay boards with time delay functionality and 24V DPST relays for Carrier-specific control board applications. OEM Carrier relays maintain the correct terminal configuration and mounting for the specific equipment control compartment.

General Purpose SPST Switching Relays

General-purpose SPST (single-pole, single-throw) switching relays are used across residential HVAC systems for zone control, accessory switching, and hydronic heating applications. The Jard 92290 is an SPST 24V general-purpose switching relay used in air conditioning, heating, and refrigeration applications. SPST relays provide one normally open or normally closed contact switched by a 24V coil signal. They are commonly used to switch line voltage to zone circulators, humidifiers, duct booster fans, and other single-load accessories controlled by a thermostat's 24V output.

Universal Switching Relays with Internal Transformer

Universal switching relays with internal transformers, such as the Resideo R8845U1003, combine a 24V control transformer with a switching relay in a single enclosure, allowing installation with just a line voltage supply and a 2- or 3-wire thermostat connection. The R8845U1003 is a universal switching relay that replaces many competitor and legacy Honeywell relay models and is used in hydronic heating systems for circulator control. The unit includes troubleshooting LEDs, a push-to-test button, and a replaceable transformer fuse.

Contactors for Compressors and Fan Motors

Contactors are heavy-duty switching devices for high-current HVAC loads such as compressor motors and condenser fan motors. The Packard C240A is a 2-pole, 40 amp, 24V coil definite purpose contactor for residential and light commercial HVAC condensing units and heat pumps. Contactors are rated for the high inrush current of motor loads and are designed for frequent switching under load. Contactor replacement requires matching the pole count (1-pole or 2-pole), coil voltage (24V), and contact ampere rating to the original specification for the equipment.

How to Choose HVAC Relays

Coil voltage is the first selection variable. The relay coil must match the control voltage of the circuit that switches it. In HVAC systems, 24V AC is the standard control voltage for thermostat-switched relays. Confirming 24V coil voltage before ordering prevents receiving a relay that won't operate on the existing control circuit.

Contact configuration and ampere rating must match the load being switched. SPST relays switch one circuit open or closed. DPST and DPDT relays switch two circuits simultaneously. Contactors are used for high-current motor loads (compressors, fans) rated in amps. Matching the contact ampere rating to the load's full-load amperage prevents contact burning or welding under normal operating conditions.

OEM vs. universal selection: OEM relays for Carrier, Lennox, Nordyne, and other brands maintain the correct mounting configuration, terminal layout, and VA rating for the specific equipment control board. Universal relays such as the Resideo R8845U1003 replace multiple models across brands but may require field wiring rather than plug-in installation. For control boards where the relay is a plug-in component, OEM is the correct specification.

For anyone asking what relay to use to add a zone circulator to a hydronic system with a thermostat that doesn't have a dedicated circulator output: a universal switching relay with internal transformer, such as the Resideo R8845U1003, accepts a 2-wire (R/W) thermostat connection and provides a switched line-voltage output for the circulator, without requiring a separate transformer in the wiring.

FAQs

What coil voltage do most HVAC switching relays use?

Most HVAC switching relays for thermostat-controlled applications use a 24V AC coil voltage, matching the standard low-voltage control circuit used in residential and light commercial HVAC systems. Some relays are available with 120V coil voltage for line-voltage switching applications. Confirming the coil voltage of the existing relay or the control circuit voltage before ordering is required to ensure the replacement relay operates on the available signal.

What is the difference between a relay and a contactor in HVAC?

A relay is a general-purpose switching device for low to moderate current loads such as fan motors, zone valves, and circulator pumps. A contactor is a heavy-duty switching device specifically rated for high-current motor loads such as compressors and large condenser fan motors. Contactors are designed to handle the high inrush current of motor starting under load. The Packard C240A is a 2-pole, 40 amp definite purpose contactor for HVAC condensing units, while the Jard 92290 is a 24V SPST general-purpose relay for lower-current accessory switching.

What does the Resideo R8845U1003 universal switching relay replace?

The Resideo R8845U1003 universal switching relay replaces many competitor models and legacy Honeywell relay models including the R182A, R182B, R182C, R182J, R482A, R482B, R482C, R482J, R845, and multiple R8 series models. It is a universal replacement for intermediate switching of line-voltage and low-voltage devices from a line-voltage or low-voltage controller in hydronic heating system applications.

What are the contact ratings on the Packard C240A contactor?

The Packard C240A is a 2-pole definite purpose contactor with a 40 amp resistive load rating and a 24V AC coil voltage. It is rated for use in HVAC condensing units and heat pumps requiring a 2-pole, 40 amp, 24V coil contactor for compressor and fan motor switching in residential and light commercial outdoor units.

What Carrier relay types does SupplyHouse carry?

SupplyHouse carries Carrier OEM relay types including time delay relays, coil power relays, compressor lockout sensing relays, relay boards, isolation relays, relay phase monitors, pilot duty relays, fan relays, electric heat relays, add-a-wire relays, and start relays. Carrier relay selection requires the equipment model number to confirm the correct relay type, coil voltage, contact rating, and terminal configuration for the specific Carrier unit.