AC Compressor Problems: Turning On and Off, and a Bad Compressor

What the compressor is, and what people mean by the word

The Energy Saver guide from the Department of Energy describes a split system as an outdoor unit holding the condenser and compressor, plus an indoor unit. EPA's FAQ page says the condensing unit contains the condenser coil and compressor, and the indoor coil is the evaporator.

The Energy Saver guide also uses the word for the whole outdoor unit. Its tip says to keep the compressor, the part of the unit outside, clean to prevent overheating. Our reading: a compressor that seems not to turn on may be a fan, capacitor or contactor problem. A contactor is the relay that connects the compressor to power. AC not turning on covers those checks.

Normal cycling, short cycling and the built-in pause

Cycling means the compressor starts and stops as the thermostat calls for cooling. Short cycling means it starts again and again after only brief runs. Our reading: no document below sets a number that proves a given home system is short cycling.

Danfoss makes scroll compressors, a design in which two spiral parts squeeze the refrigerant gas. Its application guidelines cover light-commercial and large-commercial models, not a particular home. They recommend a restart delay timer to limit compressor cycling. They say there must be no more than 12 starts per hour, and that a higher number reduces the service life of the motor-compressor unit. They recommend a three-minute time-out. They also say the system must be designed to give a minimum running time of 2 minutes, so the motor cools after start-up and oil returns to the compressor.

Rheem's instructions for its residential heat pump outdoor units describe a time delay control. It keeps the compressor off at least 5 minutes after a power failure or thermostat shut-off. Rheem says this lets system pressure equalize, so the compressor is not damaged and fuses are not blown at start-up. Rheem also warns that the unit may start suddenly and without warning. Its control tries to restart the compressor when the delay ends or a pressure control resets. Stay clear of the outdoor unit and leave its panels closed.

Under electric control failure, the same Energy Saver guide says the compressor and fan controls could be worn out. It blames the system turning off and on too frequently. It tells the reader to contact a professional to check the unit's electrical connections.

Our reading: a pause of several minutes before a restart is by design, and the makers' figures are limits for their own equipment. An oversized system is one reason for frequent cycling, and humidity with the AC running explains why.

When a compressor stops to protect itself

Rheem's instructions say the compressor has an internal overload protector, a safety device built into the compressor. They say that under some conditions it can take up to 2 hours for the overload to reset. They say to make sure it has had time to reset before condemning the compressor. A chart in the same document says to wait at least 3 hours for an overload to reset. Our reading: the two figures differ, and both show that a compressor that has stopped may be a protected compressor, not a failed one.

Rheem says its high-pressure and low-pressure controls, on the models that have them, keep the compressor from operating in pressure ranges that can cause damage. On models with its enhanced defrost control, the compressor and fan motor stop when the high-pressure control opens. They start again after the high-side pressure drops and the control resets on its own. If the control opens 3 times within one call for heating or cooling, that defrost control locks out the compressor and outdoor fan.

Danfoss's guidelines for its commercial compressors say that when a safety switch trips, the compressor must stop immediately. It must not restart until the tripping condition is back to normal. Where possible, they recommend limiting automatic restarts after a motor-protection or low-pressure trip to less than 3 to 5 times in 12 hours, managed as a manual reset. Our reading: both makers' logic is to stop the compressor first and restart it only when set conditions are met. A unit that keeps stopping is a reason to call a licensed contractor.

What the makers' charts list as possible causes

One symptom can have many possible causes, and the makers' own charts show it. Daikin Comfort's troubleshooting chart for its condensing units lists symptoms in columns and possible causes in rows. Under the symptom compressor cycles on overload, it marks low voltage, unbalanced power and too little or too much refrigerant. It also marks noncondensibles, recirculated condenser air, a restricted liquid line and three expansion-valve conditions. Noncondensibles are gases, such as air, that do not condense in the refrigerant circuit, and recirculated condenser air is hot air from the outdoor unit drawn back into it. The expansion valve is the metering device that feeds refrigerant to the indoor coil. None of the causes the chart marks under that symptom is a fault inside the compressor. Under compressor runs, goes off on overload, it also marks a shorted or grounded compressor and a stuck compressor. Alongside those, it marks loose connections, wiring, capacitor, contactor, voltage, refrigerant overcharge and expansion-valve causes.

Rheem's service chart for short cycling of the compressor lists a faulty pressure control and loose wiring. It also lists thermostat causes, such as its location in the supply air stream, and expansion-valve problems. The chart adds low refrigerant charge, low evaporator airflow from a dirty coil, dirty filter or restricted duct, a faulty run capacitor and a faulty internal overload. Our reading: the two lists differ, and most entries sit outside the compressor, so a symptom alone cannot name the cause.

The Building America guideline from the Department of Energy says too much refrigerant can let liquid refrigerant reach the compressor and slug it. Slugging means liquid entering a machine built to pump gas. It says too little refrigerant can lead to ice on the indoor coil and can shorten compressor life. It also says moisture left in the system reacts to form acids that erode the compressor's surfaces and can cause compressor failure. These causes are covered in AC refrigerant leak repair, the evaporator coil, air filters, why an AC freezes up and AC installation done right.

Tampa Bay: storms, lightning and salt air

According to the National Weather Service in Tampa Bay, late May through June is when severe storms are most likely. It says frequent lightning continues through the July to early September peak of the rainy season. Surges are covered in AC surge protection in Florida, and salt air in coastal coil protection.

Repair the compressor, replace the outdoor unit or replace the system

EPA's FAQ page says you can continue to repair an existing air conditioning system, including replacing a major component like a condensing unit or compressor. EPA adds that compressors made for R-410A after January 1, 2025 must be labeled for servicing existing equipment only. Our reading: EPA's FAQ page still carries older dates for whole new systems, because a 2026 final rule changed the installation rule. R-410A after 2025 explains the rules that apply today.

On replacing only the compressor, the Building America guideline says the size and condition of the condensing coil is a determining factor of efficiency. It says replacing a compressor in an older system that has a large coil in good condition could be much more cost-effective than full replacement. For the bigger decision, see how to decide between repair and replacement.

After a compressor failure: acid, filter driers and who does the work

Daikin's installation reference says that when a system is replaced because of an electrical failure of the compressor, the installer should assume acid is in the system. It points to the maker's compressor burnout clean-up procedure in its service manual. Rheem's instructions for replacement units say a liquid line filter drier must be installed, and that the oil should be tested for acid. If the test is positive, they say, a suction line filter drier is mandatory. According to the Department of Energy, a filter drier removes moisture, acid, sludge and particles from the refrigerant system. Our reading: ask whether acid will be tested for and cleaned out, not only whether a part will be swapped.

Refrigerant and high-voltage work on the outdoor unit belongs to licensed or certified professionals. EPA's Section 608 rules cover who needs certification and why.

What one maker's warranty form says about a compressor

A warranty can change the repair-or-replace answer, so read yours before agreeing to a plan. One maker's limited-warranty form for condensing units is dated December 2011. It lists the compressor on its own line, with years of coverage that depend on the owner and on registration. If a part fails because of a defect during the warranty period, the maker supplies a new or remanufactured part at no charge for the part. It excludes labor and other costs of diagnosing, removing or installing parts. It does not cover the cost to replace, refill or dispose of refrigerant. It also excludes failure to start due to voltage conditions, blown fuses or open circuit breakers. It excludes failure or damage from lightning, floods, winds and corrosive environments. Our reading: that form is one example from 2011, and other makers' and newer forms differ, so ask for the one that applies to your equipment. Warranty transfer in Florida covers what happens to a warranty when a home is sold.

What to ask before a compressor is condemned or replaced

1. What measurement shows the compressor itself has failed? Rheem tells service people to give an internal overload time to reset before condemning a compressor.
2. What else was checked: supply voltage, the capacitor and contactor, refrigerant charge, airflow and thermostat settings? The Daikin and Rheem charts list all of these among possible causes.
3. What caused the failure, and has that cause been corrected? Our reading: a replacement compressor fitted without removing the cause can meet the same fault.
4. Will the system be tested for acid, cleaned if acid is found, and fitted with a new filter drier? Daikin and Rheem both give instructions on this.
5. Is the offer a compressor only, a new outdoor unit or a new system, and which refrigerant rules apply? R-410A after 2025 covers the rules for new systems and replacement parts.
6. What does the warranty cover for the compressor part, the labor and the refrigerant, and was the equipment registered?
7. Is the person doing the work certified under EPA Section 608, and does the Florida license verify with DBPR?

Get the answers in writing before work starts. For another view, see second opinions on AC repairs. Leave the outdoor unit's panels closed, because the cabinet holds line voltage and refrigerant.