AC compressor replacement cost (and when it's not worth it)

The compressor is the pump in the outdoor unit that moves refrigerant through the system. It is the most expensive single part in an air conditioner. The table shows the figures This Old House publishes by unit size.

The same page gives labor at $113 per hour, or an average flat fee of $600 for the replacement. Published figures for this repair vary between guides, so treat them as a rough guide and expect quotes above the table for larger or premium units.

• The compressor. Price depends on the tonnage and on the type. Scroll compressors are the most common in homes. Two-stage and variable-speed compressors cost more.
• Labor. The technician recovers the refrigerant, cuts out the old compressor, brazes in the new one, replaces the filter drier, pulls a vacuum and recharges the system. It takes several hours.
• Refrigerant. The full charge has to be replaced. The cost depends on the refrigerant type and how many pounds the system holds.
• Other parts. A new capacitor and contactor are often fitted at the same time.

Check the warranty before you approve anything. If the compressor is still under the manufacturer's parts warranty, you pay for labor, refrigerant and small parts only. Fixr lists that under-warranty cost at $600 to $2,650.

Have the model and serial number from the outdoor unit's data plate ready. The contractor or the manufacturer can confirm whether the unit was registered and what is covered. Labor is rarely included in a manufacturer warranty.

This Old House gives two rules of thumb. Repair makes sense if the AC is under 10 years old and the repair costs under $1,000. Replacement makes sense if the bill is more than 50% of a new unit's price or the system is over 10 years old.

There are practical reasons behind those rules. A compressor often fails because of another problem, such as a refrigerant leak, a dirty coil or an electrical fault. If that cause is not fixed, the new compressor is at risk too. And on an older unit, you are putting the most expensive part into a system whose coil, fan motor and controls are the same age.

Ask for both prices: the compressor replacement and a full replacement of the outdoor unit or system. The repair or replace calculator helps you weigh the two using your unit's age and the quote.

A compressor that will not start is often blamed when the real fault is a capacitor, a contactor or a wiring problem, all of which cost far less. Ask the technician what tests were done, such as the winding resistance and the amp draw, and what the readings were. On a repair this size, a second opinion is reasonable. The page on bad AC compressor symptoms explains the signs and your options.