What Size Capacitor Do I Need for My AC Unit?

Choosing the Right AC Capacitor#

A failed capacitor is one of the most common reasons an air conditioner stops working. Fortunately, it's also one of the easiest and cheapest parts to replace. But you must get the exact right part.

1. Match the Microfarads (µF or MFD)#

This is the most critical specification. It typically looks like:

35 µF (Single run capacitor)
45/5 µF (Dual run capacitor)

You must match this number exactly.

If you use a lower value, the motor/compressor won't run efficiently or start.
If you use a significantly higher value, you risk overheating the windings.

2. Match or Exceed the Voltage (VAC)#

Your original capacitor likely says 370 VAC or 440 VAC.

You CAN use a 440V capacitor to replace a 370V one. (Higher is fine).
You CANNOT use a 370V capacitor to replace a 440V one. (Lower is dangerous).

Rule of thumb: When in doubt, buy the 440V version. It works for both 370V and 440V systems.

3. Physical Shape (Oval vs. Round)#

Round
Oval

Electrically, they are identical. If a round capacitor fits in the space of an oval one (with a new strap), it will work. However, simple replacement is easiest if you match the shape.

Frequently Asked Questions#

Can I use a "Turbo" or Universal capacitor?#

Yes. Universal capacitors have multiple terminals that allow you to "build" the capacitance you need by connecting jumpers. They are great for service trucks but are more expensive than specific values.

My capacitor is swollen. Is it bad?#

Yes. If the top of the capacitor is domed or bulging (like a soda can about to explode), it has definitely failed. However, a capacitor can also be bad while looking perfectly normal.

Choosing the Right AC Capacitor#

1. Match the Microfarads (µF or MFD)#

This is the most critical specification. It typically looks like:

35 µF (Single run capacitor)
45/5 µF (Dual run capacitor)

You must match this number exactly.

If you use a lower value, the motor/compressor won't run efficiently or start.
If you use a significantly higher value, you risk overheating the windings.

2. Match or Exceed the Voltage (VAC)#

Your original capacitor likely says 370 VAC or 440 VAC.

You CAN use a 440V capacitor to replace a 370V one. (Higher is fine).
You CANNOT use a 370V capacitor to replace a 440V one. (Lower is dangerous).

Rule of thumb: When in doubt, buy the 440V version. It works for both 370V and 440V systems.

3. Physical Shape (Oval vs. Round)#

Round
Oval

Electrically, they are identical. If a round capacitor fits in the space of an oval one (with a new strap), it will work. However, simple replacement is easiest if you match the shape.

Frequently Asked Questions#

Can I use a "Turbo" or Universal capacitor?#

My capacitor is swollen. Is it bad?#

Yes. If the top of the capacitor is domed or bulging (like a soda can about to explode), it has definitely failed. However, a capacitor can also be bad while looking perfectly normal.

What Size Capacitor Do I Need for My AC Unit?

Choosing the Right AC Capacitor#

1. Match the Microfarads (µF or MFD)#

2. Match or Exceed the Voltage (VAC)#

3. Physical Shape (Oval vs. Round)#

Frequently Asked Questions#

Can I use a "Turbo" or Universal capacitor?#

My capacitor is swollen. Is it bad?#

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Choosing the Right AC Capacitor#

1. Match the Microfarads (µF or MFD)#

2. Match or Exceed the Voltage (VAC)#

3. Physical Shape (Oval vs. Round)#

Frequently Asked Questions#

Can I use a "Turbo" or Universal capacitor?#

My capacitor is swollen. Is it bad?#