Capacitor & contactor replacement
Humming but not starting?Usually the capacitor.
It is the most common air conditioning failure in Fresno and one of the fastest to fix. Most are done inside an hour, on the first visit, with the part already on the truck.
Stocked on our trucks Price published below Usually same day
Does this sound like your system?
Six symptoms that point at the capacitor or the contactor rather than anything expensive.
It hums but will not start
The classic. The compressor is trying to start and cannot get the torque it needs. Left running like that, it will overheat and trip its overload.
The outdoor fan will not spin
Or it starts if you nudge it with a stick through the grille. That is a textbook capacitor symptom, and it is not a reason to keep doing it.
It struggles to start, then runs
A hard start with a noticeable delay or a dimming of the house lights. The capacitor is weak but not gone, and it is taking the compressor with it.
Clicking or chattering at the unit
A contactor rapidly pulling in and dropping out. Usually a failing coil, low control voltage or pitted contacts.
The unit will not shut off
Contactor contacts welded closed, so line voltage never disconnects. This one keeps running your compressor whether the thermostat wants it or not.
A bulging or leaking capacitor
A domed top or oily residue means it has failed physically. Visible from outside the panel, though you should not be opening that panel yourself.
Not sure which of these you have? Start with the AC won't turn on guide, or just call and describe it.
What these two parts actually do
Both are small, inexpensive and absolutely fundamental. When either fails, nothing else works.
The run capacitor
Stores and releases the starting charge
Motors need a large jolt of energy to overcome inertia and start turning, far more than they need to keep running. The capacitor stores that charge and releases it on demand. Most residential systems use a dual run capacitor serving both the compressor and the condenser fan from one can.
How it is tested: measured in microfarads against the rated value printed on the can. Most are rated within roughly six percent, so one reading below tolerance is failing even while the system still starts.
The contactor
The switch that feeds the outdoor unit
An electromagnetic relay. Your thermostat sends a low-voltage signal that energizes a coil, which pulls line-voltage contacts together and powers the compressor and fan. It does this thousands of times a season, and the contacts erode with every cycle.
How it is tested: voltage drop measured across the closed contacts, plus a visual check for pitting, and the coil verified. Burned contacts starve the compressor of the voltage it needs to start.
Being straight with you
The part is cheap. The job is not just the part.
A run capacitor is an inexpensive component. We are not going to pretend otherwise, because you can look it up in thirty seconds and we would rather tell you first than be caught out by it.
So here is the honest arithmetic. What you are paying for is a licensed, insured technician arriving today rather than Thursday, with the correct capacitance and voltage rating already on the truck. It includes the diagnostic that confirms the capacitor is actually the failure rather than a symptom of something that would destroy the new one within a month. It includes the warranty on the work, and it includes nobody in your household handling a component that stores a potentially lethal charge.
A fair price on a capacitor is not the price of the part. It is also nowhere near four figures.
Please read this
A capacitor holds its charge after the power is off
This is the part of the DIY videos that gets glossed over. A run capacitor stores electrical energy and it does not release it when you flip the breaker. It can hold a dangerous charge for a long time afterwards, and discharging one safely requires the right tool and the knowledge to use it.
People are seriously injured doing this every year. The part costs very little and the risk is entirely disproportionate to the saving.
If your outdoor unit is not working, turn it off at the thermostat and at the breaker and leave the panel closed. It is genuinely not worth it.
Do not attempt this yourself
- Capacitors retain a charge with the breaker off and the unit disconnected
- The wrong microfarad or voltage rating damages motors over time
- Replacing it without finding why it failed usually means doing it again
- Work inside the unit can affect your manufacturer warranty
- Terminals are live even when the system appears completely dead
Why capacitors fail so often in Fresno
This is a much bigger repair category here than in most of the country, and there are real reasons for it.
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Heat is what kills them
Capacitors are heat-sensitive components sitting inside a metal box in full sun, in a city that runs well over a hundred degrees for weeks at a stretch. Ambient temperature is the single biggest factor in how long one lasts, and Fresno is about as hard on them as anywhere in the country.
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Run hours
Our systems accumulate far more operating hours per season than the national average. Capacitors wear with use, so components here reach the end of their service life years earlier than the same part in a milder climate.
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A dirty condenser coil makes it worse
A coil packed with valley dust raises head pressure and makes the compressor work harder, which loads the capacitor harder on every cycle. This is one of several reasons an annual coil clean pays for itself.
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Short cycling from an oversized system
Capacitors do their work at start-up. A system that starts and stops constantly asks far more of them than one running longer, steadier cycles. More on sizing.
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They fail gradually, and measurably
This is the useful part. A capacitor does not usually die overnight — it drifts out of tolerance over months. One microfarad reading during a spring tune-up will generally tell you whether yours will survive August. See what a tune-up covers.
Published pricing
What these repairs cost in Fresno
Published because this is the part of HVAC where people most often feel they were taken advantage of, and a range you can check beforehand removes the whole question.
Both include the diagnostic, the part fitted, and verification that the system runs correctly afterwards. Where both parts have failed together, which is common, they are quoted as one job rather than two.
Capacitor questions
How much should an AC capacitor replacement cost?
In the Fresno area, typically $150 to $350 including the diagnostic, the part and verification afterwards. Contactor replacement runs similarly at $150 to $300. The part itself is inexpensive; the price reflects a licensed technician arriving the same day with the correct part stocked, confirming the capacitor is genuinely the failure, and warranting the work.
My AC hums but will not start. Is it definitely the capacitor?
It is the most likely cause, but not the only one. A pitted contactor, low supply voltage, a seized condenser fan or a genuinely failing compressor all produce the same symptom. The difference between them is a few minutes with a meter, which is exactly why the capacitor should be measured rather than assumed.
Can I replace an AC capacitor myself?
We strongly recommend against it. Capacitors store an electrical charge and hold it after the power is switched off, so they must be discharged safely before anyone touches the terminals. People are seriously injured doing this every year, and the part is inexpensive enough that the risk makes no sense.
How long does a capacitor last?
Commonly five to ten years, though considerably less in Fresno because heat and high run hours are the two things that shorten their life most. Testing yours annually during maintenance is the practical way to avoid finding out on a Saturday in July.
Why did my new capacitor fail so quickly?
Usually because whatever killed the first one was never addressed. A fouled condenser coil, a seized fan motor, a failing compressor drawing high amps or a system short cycling will all destroy a replacement. If a capacitor has failed twice in a short period, the capacitor is not the actual problem.
What is a hard start kit and do I need one?
It is an additional capacitor and relay that gives the compressor extra starting torque. On a compressor that is struggling to start but otherwise healthy, it can help. It is not a substitute for a failed run capacitor and it will not rescue a failing compressor, so it should be a considered recommendation rather than an automatic add-on.
Can you come out today?
Usually yes. Capacitors and contactors are stocked on our vehicles, so most of these repairs are completed on the first visit. We are open 24 hours a day, seven days a week — call (559) 520-4240 and we will give you an honest arrival window.
Most of these are fixed in under an hour
Part on the truck, price known before we start, and the reason it failed checked as well.
Prices shown are typical ranges for the Fresno area and are not quotes. Do not attempt capacitor replacement yourself — capacitors retain an electrical charge after power is disconnected. California Heating & AC Repair is operated by Craftline Renovations, Inc. · CSLB License #999179 · Licensed and insured.