AC Repair: 12 Most Asked Questions Answered

How do you tell if your home AC compressor is bad?
How do you test an AC capacitor?
How do you make an AC compressor come on?
How do you flush an AC system after a compressor failure?
What are the symptoms of a bad AC compressor?
What does a bad AC compressor sound like?
How do you free a locked up AC compressor?
How do you tell if your home AC compressor is running?
How do you discharge an AC capacitor?
How much does it cost to replace an AC compressor?
Why is my AC running but not cooling?
Can I use my AC when water is leaking?

How do you tell if your home AC compressor is bad?

A bad AC compressor usually shows as an outdoor unit that hums but does not start, warm air from the vents while the indoor fan still runs, and a breaker that trips every time the system tries to run. Loud grinding or clanking from the outdoor unit points the same way.

The compressor is the pump that moves refrigerant, so when it fails the house stops cooling even though the indoor fan still blows. Hard starting that dims the lights is another sign. Many of these symptoms also come from a weak capacitor or a failed contactor, which cost far less to fix, so a technician should test the electrical parts before anyone calls the compressor dead.

How do you test an AC capacitor?

A technician tests an AC capacitor with a meter that reads capacitance, after the power is shut off and the capacitor is safely discharged. The reading is compared to the rating printed on its label. A capacitor outside its range, or one that is swollen or leaking oil, needs replacing.

Homeowners should not try this. A capacitor can hold a dangerous charge even with the breaker off, and a shock from one can seriously hurt you. If your unit hums and will not start, or the fan is slow to spin, call a licensed pro. A capacitor swap is usually a quick repair when it is the real problem.

How do you make an AC compressor come on?

To make an AC compressor come on, set the thermostat to cool and several degrees below room temperature, confirm the breaker and the outdoor disconnect are on, and replace the thermostat batteries if it has them. If the compressor still will not start, a technician needs to find out why.

If the simple checks pass, the cause is usually a failed capacitor, a worn contactor, a safety switch that tripped, or a compressor problem. Do not force the contactor closed or jump the unit, because that can burn out the compressor or hurt you. Shut the system off, since a unit that keeps trying to start makes damage worse.

How do you flush an AC system after a compressor failure?

Flushing an AC system after a compressor failure is done by a licensed technician. It involves recovering the old refrigerant, which requires EPA certification, and removing contaminated oil and debris from the lines and coils. Skipping it lets acid and metal particles destroy the replacement compressor.

A burned out compressor can send acid and metal particles through the system. The pro will also replace the filter drier, and may recommend a new line set or a full replacement if the damage is widespread. On an older unit, replacing the whole system often makes more sense than flushing and installing a new compressor. Ask for both options so you can compare.

What are the symptoms of a bad AC compressor?

The symptoms of a bad AC compressor are warm air from the vents, a humming or clicking outdoor unit that will not start, loud grinding or rattling, a tripped breaker, and an outdoor unit that shuts off soon after starting. The system may also run constantly without cooling the house.

You may also see ice on the refrigerant lines. In Arizona summers a struggling compressor often fails on the hottest afternoon, because heat adds load. These symptoms overlap with simpler problems like a bad capacitor, so have the electrical parts and refrigerant charge checked before agreeing to a replacement. Turn the system off if you hear metal on metal.

What does a bad AC compressor sound like?

A bad AC compressor can sound like loud grinding, rattling, screeching, or a deep clanking from the outdoor unit. A heavy hum followed by a click usually means the compressor is trying to start and cannot, which can be a locked compressor or a weak capacitor.

A short, loud knock when the unit starts can point to internal damage. Some noise is normal, like the fan and a steady low hum, so pay attention to anything new or harsh. If you hear metal on metal, turn the system off at the thermostat and the breaker and call for service, since running it can turn a repair into a replacement.

How do you free a locked up AC compressor?

A locked up AC compressor generally cannot be freed by the homeowner, and tapping it or forcing it can cause more damage. It may be seized from internal wear, or it may only seem locked because the start capacitor has failed. A technician has to check which.

Signs include a loud hum, the breaker tripping, and no startup. A technician checks the capacitor and the electrical supply first, then measures the compressor windings to see if it is truly seized. If it is, replacing the compressor or the whole outdoor unit is the real fix, depending on the age of the system and its refrigerant type. Turn the unit off until it is looked at.

How do you tell if your home AC compressor is running?

To tell if your home AC compressor is running, go to the outdoor condenser, set the thermostat to cool, and check that the large fan on top is spinning and you can hear a steady low hum from the cabinet. A silent unit with warm vent air suggests the compressor is not running.

Another check is the two refrigerant lines at the indoor coil: the larger one should feel cool and the smaller one warm when the compressor works. Stay clear of the electrical parts and never open the access panel. If the fan spins but you doubt the compressor, a technician can confirm in a few minutes.

How do you discharge an AC capacitor?

An AC capacitor should be discharged only by a licensed technician, because it can hold a charge strong enough to cause a serious shock even after the power is off. Pros use a resistor tool made for the job and a meter to confirm it is empty before touching anything.

Shorting the terminals with a screwdriver, which some videos show, can damage the capacitor, make sparks and hurt you. If you suspect a bad capacitor because the unit hums or struggles to start, turn off the thermostat and breaker, stay out of the electrical compartment, and call a pro. The swap itself is usually a short visit.

How much does it cost to replace an AC compressor?

The cost to replace an AC compressor depends on the system's age, the refrigerant it uses, the compressor type and size, the labor to recover and recharge refrigerant, and whether other parts need work. On an older system it is often close enough to a new outdoor unit that replacing the unit wins.

Newer units may still be repairable, but the compressor is one of the most expensive parts, and some refrigerants are costly or phased out. Ask any contractor for a written quote on both a compressor swap and a replacement, so you can compare the repair, the remaining life of the unit and the equipment you would have.

Why is my AC running but not cooling?

An AC runs but does not cool most often because of a dirty air filter or coil, a low refrigerant charge from a leak, a failed capacitor or compressor, or an outdoor unit choked with dust. A frozen evaporator coil from blocked airflow can also keep the house warm.

Start with what is safe: replace a clogged filter, check that all vents are open, and make sure the outdoor unit is not covered in debris. If the air is still warm after that, shut the system off and have it checked. Running a frozen or low-charge system can damage the compressor, and a refrigerant leak must be repaired by a certified technician.

Can I use my AC when water is leaking?

It is best not to use your AC when water is leaking. Turn it off and fix the leak first. Water usually comes from a clogged condensate drain line or a frozen evaporator coil, and running the system can push more water into the drain pan until it overflows into the ceiling, walls or floor.

If the water is near electrical parts, that is also a safety concern. You can switch the system off at the thermostat, clear a surface clog if you can see one, and mop up. If it keeps leaking, call a technician. In the Arizona summer, a fast repair also keeps the house from getting too hot while you wait.