AC not starting or fan not spinning? It might just be the capacitor

The capacitor is the most common AC repair in Las Vegas — and one of the fastest to fix. Here’s what it does, why it fails in the desert heat, and our flat-rate price for both dual and single capacitors.

  • Flat-rate price — confirmed before we start
  • Same-visit repair in most cases
  • USA-made MARS capacitors — on every truck
  • Clubb 33 members pay $0

What Is an AC Capacitor?

The capacitor is the component that gives your motors the electrical push they need to start and run.

Inside an AC capacitor are two long sheets of very thin metal, insulated from each other by an ultra-thin layer of plastic and immersed in oil to help manage heat. The two metal sheets never touch — instead, electrons gather and discharge across them with every cycle of the alternating current. That charge and discharge cycle is what gives the capacitor its ability to store and release electrical energy rapidly.

In a residential AC system, the run capacitor stays in the circuit the entire time the system is running — not just at startup. It continuously provides a phase-shifted current to the start winding of the motor, which is what creates the rotating magnetic field that keeps the motor spinning efficiently at the correct speed and torque. Without a functioning capacitor, a motor either can’t start at all, runs slower than it should, draws more current than rated, and overheats — or some combination of all three.

A weak or failed capacitor is one of the leading root causes of motor burnout. A motor running without proper capacitor support works harder to develop torque, runs hotter, and wears out significantly faster. This is why we always replace the capacitor when we replace a motor — and why catching a weak capacitor at a maintenance visit can save a motor that would otherwise fail within a season.

Dual Run Capacitor vs Single Run Capacitor

There are two types of run capacitors in residential HVAC — dual and single. Most homes have a dual. Here’s the difference.

Dual Run Capacitor

Most common — serves both the compressor and condenser fan motor

How it works:

A dual capacitor houses two separate capacitor sections inside one cylindrical shell — one side serves the compressor (HERM terminal) and the other side serves the condenser fan motor (FAN terminal). Both share a common terminal (C). Rather than having two separate capacitors in the cabinet, the dual design combines them into one compact unit.

Rated for:

  • Two microfarad ratings — one for compressor, one for fan (e.g., 45/5 MFD)
  • 370 or 440 volts — both ratings work on standard 208-230V residential systems
  • Found on the vast majority of split systems and package units

•  The most commonly replaced capacitor in residential HVAC

Single-Pole Contactor

Serves one motor only — compressor or fan, not both

How it works:

A single run capacitor serves only one motor — either the compressor or the condenser fan motor, but not both. Some systems are designed with two separate single capacitors instead of one dual. Single capacitors have one microfarad rating and two terminals.

Rated for:

  • One microfarad rating — serves one motor only
  • 370 or 440 volts — same voltage standards as dual
  • Found on some older systems, certain package units, and higher-end equipment with dedicated capacitors per motor

•  Less common than the dual in standard residential equipment

What does MFD mean?

MFD stands for microfarad — a unit of electrical capacitance that measures how much charge the capacitor can store and release. A dual capacitor rated 45/5 MFD has a 45 MFD section for the compressor and a 5 MFD section for the fan motor. Both sides must be within 10% of their rated value to be considered healthy — beyond that, replacement is needed.

What does voltage rating mean?

The voltage rating on a capacitor (370V or 440V) is the maximum voltage the capacitor can safely handle. Both ratings work on standard 208-230V residential systems — a 440V-rated capacitor is simply built with more headroom. A higher voltage rating on the replacement is acceptable; going lower is not.

Why Capacitors Fail in Las Vegas

Capacitors fail faster in Las Vegas than almost anywhere else in the country. Three factors drive this.

Factors Why it matters here
Heat Capacitors contain oil to help dissipate heat. But oil has its limits. When the ambient temperature inside the outdoor cabinet climbs to 140°F or higher in a Las Vegas summer — which it does regularly — that heat breaks down the capacitor's dielectric material and oil over time, reducing the microfarad rating and eventually causing failure. Capacitors are rated for a maximum operating temperature, and Las Vegas routinely pushes them to or past that limit.
Continuous runtime Every cycle of alternating current causes electrons to gather and discharge across the capacitor's internal metal plates. In a city where AC systems run 14+ hours a day in summer, a capacitor completes an enormous number of charge and discharge cycles per season. That wear accumulates faster here than in moderate climates where systems cycle far less.
Voltage events Las Vegas power grid events — summer storms, heavy grid load, momentary spikes — create electrical stress on capacitors. Each high-voltage event slightly degrades the thin plastic insulation between the metal plates inside the capacitor. Over enough events, the capacitor reading drops below the 10% tolerance threshold and the motor it serves begins to struggle.

Signs Your Capacitor Has Failed

What you notice What it likely means
AC hums but the outdoor fan isn't spinning The compressor may be running — you can hear it — but the fan blade isn't moving. The motor is trying to start but can't develop enough torque without capacitor support. This is one of the clearest signs of capacitor failure.
System tries to start then immediately shuts off The compressor or fan draws high locked-rotor amperage at startup, the breaker or internal overload trips, and the system shuts down. Without the capacitor providing the correct phase-shifted current, the motor never reaches running speed.
Lights flicker or dim when the AC turns on A struggling motor draws significantly more current during a hard start — that extra load is enough to dip voltage momentarily in the home. A healthy capacitor smooths out startup current; a failed one doesn't.
AC running but not cooling well A weak but not yet failed capacitor allows the motor to run — but slower than designed. A condenser fan running below rated speed moves less air across the coil, head pressure builds, and the system loses cooling capacity without shutting down completely.
Outdoor unit hot to the touch after shutdown Reduced fan airflow from a struggling motor means heat isn't being rejected efficiently. The unit retains more heat than normal after shutting down.
Capacitor looks swollen, bulged, or leaking oil A failed capacitor will sometimes show physical damage — a bulged top or sides, or oil residue around the casing. If you can see the capacitor, this is a visual confirmation. Most of the time failure happens internally with no visible change.

Important — do not touch the capacitor.

A capacitor stores an electrical charge even after power has been disconnected. It must be safely discharged before handling. Our technicians do this as standard procedure on every service call involving electrical components.

Flat-Rate Pricing

We price capacitors by type — dual or single. One flat-rate price covers any size within that type. The microfarad rating and brand of the original don’t change the price. We bring both on the truck and replace whichever your system needs.

Dual Run Capacitor

$ 250
  • Compressor + fan motor — any MFD size
Standard

CLUBB 33

$ 0
  • USA-made MARS capacitor
  • 5-year warranty
  • Any MFD rating — same price
  • Usually fixed same visit

Single Run Capacitor

$ 220
  • One motor only — any MFD size
Standard

CLUBB 33

$ 0
  • USA-made MARS capacitor
  • 5-year warranty
  • Any MFD rating — same price
  • Usually fixed same visit

Clubb 33 — $33/month. Both dual and single capacitor replacements are $0 for members.

$3,000 repair credit per visit covers the full cost of any capacitor replacement. Join at VegasAC.com/clubb-33

Why We Use MARS Capacitors

We stock MARS USA-made capacitors on every truck.

The same brand we trust for motors, we trust for capacitors.

MARS — Motors & Armatures, Inc. — manufactures their run capacitors in the United States. Their USA-made capacitor line meets EIA-456A test standards, carries a 5-year warranty, and covers the full range of residential microfarad ratings we need for both dual and single applications.

Feature What it means
Made in the USA MARS capacitors are manufactured domestically. Not imported, not of unknown origin. We chose them for the same reason we chose their motors — quality we can stand behind.
EIA-456A tested EIA-456A is the industry standard test specification for motor capacitors. Every MARS USA capacitor is tested to this standard before leaving the factory, verifying that the microfarad rating is accurate and the capacitor will perform as rated.
Oil-filled dielectric The dielectric fluid inside the capacitor dissipates heat and protects the internal metal plates. This is what allows the capacitor to survive the extreme temperatures inside an outdoor cabinet during a Las Vegas summer.
5-year warranty MARS stands behind their capacitors for 5 years. Orange Air also backs every installation with our own 5-year labor warranty — if the capacitor we install fails within that window, we come back.
Full MFD range on the truck MARS dual and single run capacitors cover the complete residential microfarad range. We don't have to special-order a size — whatever your system needs, we have it on the truck.
Same price regardless of size Because MARS multi-rating capacitors cover multiple MFD values, our pricing is the same for any size within each type. Dual is $250, single is $220 — no matter what the original rating was.

What the Technician Does on a Capacitor Call

We don’t guess. Before any capacitor is replaced, we measure.

Step What we do
1 Disconnect and discharge Power is disconnected at the outdoor disconnect before approaching any capacitor. The capacitor is then safely discharged — it holds a charge even after power is off and must be handled correctly before testing or removal.
2 Capacitance measurement We measure the actual microfarad reading on both sections of the capacitor using a meter capable of capacitance measurement. If the reading is more than 10% below the rated value on either section, the capacitor has failed — even if it hasn't completely stopped working yet.
3 Visual inspection We inspect the capacitor casing for bulging, swelling, or oil leakage — physical signs of internal failure.
4 Replacement with correct rating We match the replacement to the correct MFD rating and voltage rating for your system. Higher voltage rating is acceptable; lower is not. The new capacitor is secured properly and all terminals connected firmly — loose terminals are a common cause of repeat failures.
5 Amperage check after startup After replacing the capacitor and restarting the system, we measure compressor and fan motor amperage to confirm both are drawing within their rated range. This confirms the new capacitor is doing its job.

Frequently Asked Questions

Both a failed capacitor and a failed motor can cause the outdoor fan to stop spinning. A failed capacitor will often cause the motor to hum without turning — the motor is trying to start but can't get the torque it needs. A failed motor typically makes no noise or produces grinding and squealing. Your technician will test both before recommending anything. Sometimes it is just the capacitor — which at $250 is far less than a motor at $620.

Yes — and this is one of the most important things to understand about capacitors. A motor running with a weak capacitor draws more current than rated, runs hotter than it should, and wears out its windings and bearings faster. A weak capacitor caught and replaced at a maintenance visit can prevent a motor failure that would have happened within a season. That is exactly why we check capacitor readings at every maintenance visit.

Because we carry MARS multi-rating capacitors that cover the full range of residential MFD values. The labor is the same regardless of the MFD rating. The part cost difference between sizes is small enough that we absorb it into a single flat rate rather than charging differently based on the original spec. Simple, transparent, predictable.

Always. A weak or failed capacitor is one of the most common root causes of motor failure. Putting a new motor on the same old capacitor is one of the fastest ways to shorten the new motor's life. Every condenser fan motor replacement at Orange Air includes a new capacitor at no additional charge.

In moderate climates, run capacitors often last 10 years or more. In Las Vegas, due to extreme ambient temperatures and long system runtimes, 3 to 7 years is more typical. Some fail sooner, some last longer. This is why annual maintenance matters — catching a weak capacitor before it fails completely prevents a no-cool call on the hottest day of summer.

Almost always yes. A capacitor replacement is one of the most cost-effective repairs in HVAC. Even on a 20-year-old system, if the compressor and coils are healthy, spending $250 to keep the system running another season is almost always the right call. We will tell you if the overall condition of the system changes that math.

AC not turning on? Call or text now

702-604-8092

We carry single-pole, two-pole, and three-pole contactors on every truck. Most replacements are diagnosed and completed same visit. $240 flat-rate — price confirmed before we start.

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