How Long Should an Air Conditioner Run Per Cycle?

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Measure Your AC Cycle Time and Buy Something Useful With the Savings

There are some industry misconceptions homeowners are told:

  • “Bigger AC systems cool faster and work better.”
  • “Short cycling isn’t a big deal.”

Neither is accurate.

An oversized air conditioner will cool your house.
But when it’s too large for the load, it often short cycles — and that affects efficiency, comfort, and long-term reliability.

Here’s what short cycling actually does — and what it realistically costs over 15 years.

What Is Short Cycling in an Air Conditioner?

Short cycling occurs when an AC system turns on, runs for only a few minutes, shuts off, and then turns back on again shortly after.

A properly sized residential air conditioner in Denver typically runs:

15–25 minutes per cycle on a warm day.

An oversized AC may run:

5–8 minutes per cycle.

That difference matters.

Air conditioners are designed to operate at steady state. When cycles are too short, the system repeatedly operates in its least efficient phase.

What Happens Inside an Oversized AC System?

When an air conditioner starts:

  • Compressor amperage briefly spikes
  • Refrigerant pressures are unbalanced
  • Oil circulation is stabilizing
  • The evaporator coil hasn’t fully cooled
  • The condenser hasn’t reached steady heat rejection

The first few minutes are the least efficient portion of operation.

In a 20-minute cycle, that startup period is small.

In a 6-minute cycle, startup losses become a large percentage of total runtime.

The system spends more time ramping up — and less time operating efficiently.

How Short Cycling Affects Energy Efficiency

Oversizing does not double your electric bill.

But it does reduce seasonal efficiency.

A realistic efficiency loss from frequent short cycling is:

5%–12%

This reflects:

  • Repeated startup energy losses
  • Reduced steady-state operation
  • Lower humidity removal efficiency
  • Increased cycling losses

Let’s apply the math.

Short Cycling Energy Cost Example

Assume a typical 3-ton air conditioner uses:

3,000 kWh per cooling season

At $0.15 per kWh.

5% Efficiency Loss

150 extra kWh
$22.50 per year

10% Efficiency Loss

300 extra kWh
$45 per year

12% Efficiency Loss

360 extra kWh
$54 per year

Not dramatic.

But consistent.

Over 15 years:

$330–$810 in additional electricity.

Short cycling doesn’t destroy efficiency.

It quietly reduces it.

The Bigger Cost of an Oversized AC: Mechanical Wear

Energy loss is only part of the picture.

Short cycling increases:

  • Compressor start events
  • Electrical inrush stress
  • Contactor wear
  • Motor winding temperature swings

Starting is the hardest thing a compressor does.

An oversized air conditioner may start twice as often per hour compared to a properly sized system.

Over 15 years, that can mean tens of thousands of additional starts.

Does that guarantee early failure?
No.

Does it increase probability?
Yes.

Electrical components wear by cycle count — not calendar age.

Comfort Problems Caused by Short Cycling

Oversized AC systems often remove less humidity.

Moisture removal happens after the evaporator coil becomes cold and stays cold.

Short cycles mean:

  • Less latent heat removal
  • Higher indoor humidity
  • Cooler but slightly clammy air

Homeowners often respond by lowering the thermostat further.

That increases runtime and partially offsets the “faster cooling” advantage.

Why AC Systems Get Oversized

Oversizing usually happens because:

  • Contractors use square-foot rules instead of load calculations
  • Bigger equipment feels safer
  • Companies want to avoid callbacks

But proper AC sizing isn’t about maximum cooling capacity.

It’s about matching the actual cooling load so the system runs long enough to operate efficiently.

That requires a proper load calculation — not a guess.

Is Short Cycling an Emergency?

Usually not.

But over time, it:

  • Reduces efficiency
  • Increases wear
  • Lowers humidity control
  • Raises long-term ownership cost

Short cycling is a slow financial leak — not a sudden failure.

Final Thought: Bigger Isn’t Better

Air conditioners are not harmed by running.

They are stressed by starting.

A properly sized system runs longer, starts less often, removes more humidity, and operates closer to its rated efficiency.

Over 15 years, that difference matters.

Sources:

https://www.energystar.gov/ia/home_improvement/home_sealing/RightSized_AirCondFS_2005.pdf

Premier Mechanical
AC Repair & Installation – Denver
www.claimyourcomfort.com
720.207.6812

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