Electrical & Controls for HVAC and Facilities: Capacitors, Contactors, Relays, Control Boards & More, Same-Day Shipping
Voomi Supply sells electrical components and controls for HVAC, refrigeration, and general facility use, from capacitors, contactors, and relays to control boards, meters, and backup power equipment. Order trusted brands with in-stock small parcel orders placed before 12 PM shipping same day, plus a 30-day return policy and financing at checkout.
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Product typesCapacitors, contactors, boards, meters, power
ShippingSame-day, orders before 12 PM
Returns30-day (excludes final-sale items)
FinancingAvailable at checkout
SupportUS-based experts
BrandsAllen-Bradley, ABB, Carrier & more
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Trusted BrandsAllen-Bradley, ABB & more
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MARS
MARS 14255 70/5 MFD Round Run Capacitor 440/370V
$38.53
In stock
SIEMENS
Siemens 42FE35AJ Contactor 42DP 75A 3P Open 24V
$347.17
In stock
GOODMAN
Goodman 0200054001P Limit Switch 150-45F
$54.76
In stock
RHEEM
Rheem 62-105217-01 Integrated Furnace Control Board for HVAC Systems
$339.58
$179.07
In stock
ICM CONTROLS
ICM Controls ICM493 40A Single Phase Line Voltage Monitor with Surge Protection
$491.21
$270.66
In stock
UEI TEST INSTRUMENTS
UEi Test Instruments EM152 Dual Differential Digital Manometer
$220.18
In stock
GLOBAL
Global DTK-KG2 Kool Guard 2 120/240V 40amp Surge Protector Voltage Monitor
$471.10
$238.66
In stock, final sale
Brands we carry
Why electrical & controls matter in HVAC
Nearly every HVAC failure that isn't refrigerant- or airflow-related traces back to the electrical side of the system: a weak capacitor that won't spin a motor, a stuck contactor, a blown control board, or a tripped breaker.
This category covers the components that start, protect, regulate, and power HVAC and refrigeration equipment, plus the meters and testers technicians use to diagnose them, and the generators and power supplies that keep systems running when utility power doesn't.
Voomi Supply's Electrical & Controls category supports professionals and property owners working across HVAC, refrigeration, and building electrical systems.
Who may rely on HVAC electrical & controls?
HVAC technicians
Source OEM and compatible replacement parts including capacitors, contactors, relays, transformers, control boards, igniters, flame sensors, and diagnostic tools for residential and commercial HVAC repairs.
Electricians and facility maintenance teams
Find circuit breakers, disconnects, fuses, transformers, relays, electrical testers, and other components used to install, maintain, and troubleshoot building electrical systems and mechanical equipment.
Commercial property owners and facility managers
Keep critical systems operating with replacement electrical components, backup power equipment, generators, extension cords, and electrical supplies for planned maintenance and emergency repairs.
Core electrical components: what each one does
| Component | Function | Common failure signs |
|---|---|---|
| Capacitor | Stores and releases electrical charge to start and run motors (compressor, fan, blower) | Motor hums but won't start, AC unit clicks and shuts off, capacitor case bulging or leaking |
| Contactor | Heavy-duty switch that uses a low-voltage signal to close a high-voltage circuit powering the compressor or other large loads | Unit won't start, contactor buzzing/chattering, pitted or burnt contacts |
| Relay | Low-current switch that controls a circuit via an independent control signal, often relaying between the thermostat and larger components | Fan or component fails to cycle on/off correctly, erratic operation |
| Circuit breaker | Interrupts current flow to protect a circuit from overcurrent; resettable | Repeated tripping, breaker won't reset, warm breaker panel |
| Disconnect | Provides a manual, lockable point to cut power to equipment during service | Required for code compliance and technician safety, not typically a "failure" part |
| Fuse | One-time overcurrent protection; must be replaced after it blows | Equipment dead with no reset option, visibly blown element |
| Transformer | Steps line voltage down to the low voltage (typically 24V) used by thermostats and control circuits | No power to thermostat, control board not responding |
| Sequencer | Times the staged activation of electric heat elements to prevent overloading the circuit | Electric furnace heats unevenly or trips breakers on startup |
| Timer / time delay relay | Delays or sequences equipment operation (e.g., compressor short-cycle protection) | Compressor short-cycling, defrost cycle not running on schedule |
| Control/circuit board | The central "brain" that manages ignition, blower timing, defrost cycles, and safety switches | No response to thermostat calls, error/flash codes, intermittent operation |
Relay vs. contactor: a common point of confusion
Relays and contactors look similar and are often mixed up, but they're built for different jobs. A relay is designed for low-current switching (typically up to around 10A) in control circuits. It acts as the go-between for a low-power signal and a larger load.
A contactor is a heavier-duty switch built to handle high-current, high-voltage loads directly, such as a compressor, large motor, or lighting bank.
Capacitors: start vs. run, and how to size a replacement
AC and refrigeration systems typically use three types of capacitors:
- Start capacitors deliver a short, strong burst of energy to get a motor moving from a standstill, then drop out of the circuit.
- Run capacitors stay in the circuit continuously, maintaining steady voltage to keep the motor running efficiently.
- Dual-run capacitors combine both the compressor and fan motor's run capacitor into a single unit, common in residential condensing units.
When replacing a capacitor, microfarad (µF/MFD) rating and voltage rating both need to match the original part, or fall within the manufacturer's approved tolerance. Undersized capacitance starves the motor of starting torque; oversized capacitance can overheat the motor winding. Dual-run capacitors also need to match on both capacitance values (e.g., "45/5 MFD").
Circuit boards: matching the right board to the right job
"Control board" is a broad term. HVAC and refrigeration equipment typically uses several purpose-built boards rather than one universal board.
Furnace control boards
Manage ignition sequence, blower timing, and safety lockouts in gas or electric furnaces.
Defrost control boards
Time and trigger the defrost cycle on heat pumps and refrigeration equipment to prevent coil icing.
Ignition control boards
Manage the spark or hot-surface ignition sequence and flame verification.
Fan control boards
Regulate blower speed and cycling, particularly on variable-speed systems.
Power supply control boards
Convert and regulate incoming voltage for the rest of the control system.
Display/heater/water control boards
Equipment-specific variants for thermostats, electric heaters, and water heaters.
Boards are rarely interchangeable across equipment types or even across manufacturers' model years, so confirming the exact OEM part number (or a verified cross-reference) before ordering is important to avoid a return.
Ignition components: igniters and flame sensors
On gas furnaces, the igniter and flame sensor work as a pair, though they serve different purposes. The igniter lights the burners. Most modern systems use a hot surface igniter (a silicon-based element that glows hot enough to ignite gas) or, less commonly now, a spark igniter.
The flame sensor is a safety device: it confirms a flame is actually present after ignition, and it's what shuts off the gas valve if the flame fails or goes out unexpectedly. A furnace that fires briefly and then shuts down is a classic flame-sensor symptom (often just needing cleaning); a furnace that won't ignite at all more often points to the igniter or the control board driving it.
Sizing and choosing electrical protection devices
Circuit breakers, fuses, and disconnects all protect equipment and wiring from overcurrent, but they're not interchangeable:
- Circuit breakers are resettable and sized to the equipment's minimum circuit ampacity (MCA), found on the equipment's data plate, never sized larger than the maximum overcurrent protection (MOCP) rating.
- Fuses provide one-time protection and must be replaced after tripping; time-delay ("slow-blow") fuses are typically required for motor-driven HVAC loads to tolerate normal startup surge.
- Disconnects don't provide overcurrent protection on their own, they provide a manual, lockable shutoff point required by code near outdoor condensing units and other equipment for technician safety during service.
Meters and testers: what technicians actually use
| Tool | What it measures | Typical use |
|---|---|---|
| Multimeter | Voltage, resistance (ohms), continuity, and often capacitance | General diagnostics: dead circuits, blown capacitors, bad switches |
| Clamp meter | Current (amps) without breaking the circuit | Checking motor draw against rated amperage |
| Voltage tester | Presence of voltage (non-contact or contact) | Quick safety check before servicing equipment |
| Conduit bender | Not electrical measurement, shapes conduit to route wiring | Rough-in electrical installation work |
Confirming a capacitor, contactor, or control board is actually bad starts with a multimeter check: capacitance reading against the rated µF, continuity across contactor contacts, and voltage present at the expected points on a control board.
Backup and standby power: generators and power supplies
Generators and portable power equipment serve a different but related need, keeping HVAC, refrigeration, and other critical loads running through an outage. Sizing depends on:
- Running wattage of everything intended to run simultaneously (HVAC compressors and motors draw meaningfully more at startup than while running).
- Starting/surge wattage, which the generator must also cover for the largest motor load starting up.
- Fuel type and runtime needs: portable gas/propane units for shorter outages, standby units for whole-building continuity.
- Power quality for sensitive electronics: inverter generators produce cleaner power than conventional models.
Power and extension cords, solar panels, and PTO-driven generators round out this category for job site, backup, and off-grid applications.
Before you order: verify compatibility
Electrical components are often not universally interchangeable. Before ordering, confirm:
- Voltage rating (e.g., 24V control circuit vs. 120V/208V/240V line voltage)
- Amperage/current rating appropriate to the load
- Coil voltage on relays and contactors
- Capacitance (µF) and voltage rating on capacitors, including dual-run values
- Exact OEM part number or verified cross-reference on control boards
- Single-phase vs. three-phase compatibility on motors, contactors, and generators
Common HVAC electrical symptoms and the likely part
| Symptom | Likely cause | Part to check |
|---|---|---|
| AC hums but doesn't start | Weak or failed run/start capacitor | Capacitor |
| Outdoor unit fan won't spin | Bad capacitor or seized motor | Run capacitor, contactor |
| Compressor won't start but hums | Weak run capacitor | Run capacitor |
| Unit clicks repeatedly, won't stay on | Failing or pitted contactor | Contactor |
| No power to thermostat or control board | Blown transformer or fuse | Transformer, fuse |
| Breaker trips repeatedly | Overcurrent, often from a failing motor or short | Circuit breaker, motor |
| Furnace fires briefly then shuts off | Dirty or failed flame sensor | Flame sensor |
| Furnace won't ignite at all | Failed igniter or ignition control board | Igniter, ignition control board |
| Electric furnace trips breaker on startup | Sequencer staging heat elements incorrectly | Sequencer |
| Coil ices over, no defrost cycle | Failed defrost control board or timer | Defrost control board |
Safety note
Always disconnect and lock out power before servicing any electrical component. Capacitors can retain a dangerous electrical charge even after power is removed and should be discharged properly before handling. If you're not confident diagnosing or replacing electrical components, especially line-voltage work, contact a licensed electrician or HVAC technician.
Why choose Voomi Supply for electrical & controls?
Wide selection
Find capacitors, contactors, relays, control boards, generators, diagnostic tools, and other electrical components for HVAC, refrigeration, and facility maintenance in one place.
Technical product information
Detailed specifications and compatibility information help you choose the right replacement part with confidence.
Trusted brands
Shop OEM and compatible electrical components from established manufacturers trusted by HVAC professionals.
Fast shipping
Many in-stock products ship the same day, helping reduce downtime and keep projects moving.
US-based support
Our team can help confirm compatibility and answer product questions before you order.
Electrical & controls glossary
- Capacitor
- An electrical component that stores and releases energy to help start and run HVAC motors; used as start, run, or dual-run capacitors. Shop capacitors →
- Contactor
- A heavy-duty switch that uses a low-voltage control signal to close a high-current circuit powering a compressor, motor, or large load. Shop contactors →
- Relay
- A low-current electrical switch that controls a circuit via an independent signal, commonly used to relay commands between the thermostat and larger components. Shop relays & switches →
- Circuit breaker
- A resettable safety device that interrupts current flow to protect wiring and equipment from overcurrent. Shop circuit breakers →
- Disconnect
- A manual, lockable switch installed near equipment to safely cut power during service, required by code near most outdoor HVAC units. Shop disconnects →
- Fuse
- A one-time overcurrent protection device that must be replaced after it trips. Shop fuses →
- Transformer
- Steps down line voltage to the low voltage (commonly 24V) used to power thermostats and control circuits. Shop transformers →
- Sequencer
- Times the staged activation of electric heat elements so they don't all draw power at once. Shop sequencers →
- Control board
- The central circuit board that manages ignition, blower timing, defrost cycles, and safety switches for HVAC and refrigeration equipment. Shop control boards →
- Igniter
- The component that lights the burners in a gas furnace, typically a hot surface or spark igniter. Shop ignition control boards →
- Flame sensor
- A safety device that confirms a flame is present after ignition and shuts off the gas valve if it isn't. Shop control & circuit boards →
- Multimeter
- A handheld diagnostic tool that measures voltage, resistance, continuity, and often capacitance. Shop multimeters →
- Clamp meter
- A diagnostic tool that measures current (amperage) by clamping around a wire, without breaking the circuit. Shop clamp meters →
Frequently asked questions
What electrical supplies do you offer for HVAC systems?
Capacitors, contactors, relays and switches, circuit breakers, disconnects, fuses, transformers, sequencers, control and circuit boards, plus diagnostic tools like multimeters and clamp meters, and backup power equipment including generators.
How do I know which capacitor I need?
Match the microfarad (µF/MFD) rating and voltage rating to the original part, or to the equipment manufacturer's specification. Dual-run capacitors need both capacitance values to match, not just the total.
What's the difference between a relay and a contactor?
A relay handles low-current control-circuit switching, while a contactor is built for high-current, high-voltage loads like compressors and large motors. They're often confused because they look similar, but using the wrong one can cause short cycling or equipment damage.
Can I replace a control board myself?
Basic swaps are possible for comfortable DIYers, but control boards must be an exact match (or verified cross-reference) to the original, and the power must be disconnected before servicing. If you're unsure, a licensed HVAC technician is recommended.
Why does my AC hum but not start?
This is a classic sign of a weak or failed capacitor, which can no longer deliver the starting charge the compressor or fan motor needs.
Do I need a disconnect near my outdoor AC unit?
Yes, most jurisdictions require a lockable disconnect within sight of outdoor HVAC equipment so technicians can safely cut power during service.
What tools do I need to diagnose electrical HVAC problems?
A multimeter covers most diagnostics (voltage, continuity, capacitance), while a clamp meter is useful for checking motor amp draw against rated values.
How do I size a generator for HVAC backup power?
Add up the running wattage of everything you want to power simultaneously, then make sure the generator's starting/surge wattage rating covers the largest motor's startup draw. HVAC compressors draw significantly more at startup than while running.
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CategoryCircuit breakersFeatured in the components table above
CategoryDisconnectsCode-required near outdoor units
CategoryTransformers24V control circuit power
HubHVAC equipment & systemsACs, furnaces, heat pumps
HubHVAC replacement partsControl boards, capacitors & more
HubRefrigerantR-410A, R-32 & supplies
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