The condensing unit for your central air conditioner is the portion that sits outside your house on a concrete slab. The unit holds the compressor, condenser coils, and other parts that help get the cooling system started with gas refrigerant and its passage. Problems with parts in the condensing unit can lead to the entire system shutting down unexpectedly, which will leave you without cooled air in your home.

What are a couple of the problems that can lead to an unexpected shutdown, and how can an air-conditioning installation and repair company assist you?

Broken Compressor Capacitor

The compressor starts up and compresses the gas refrigerant so that the chemical can move through the HVAC system. The compressor requires steady supplies of electricity to do that job properly, and interruptions in the utility can cause the compressor to fail. Air conditioners often have a failsafe to protect the compressor in the form of the capacitors.

Your air conditioner might have a start capacitor, a run capacitor, or both. The capacitors each store a small amount of electrical current to help the compressor stay steady while starting up and while running. If your air conditioner is starting but shutting down unexpectedly, the problem is more likely in the run capacitor.

You can perform testing if you own a multimeter with an Ohms setting. You will need to remove the charge from the capacitor first, after you've turned off the main power to the unit, by holding the end of an insulated screwdriver across the capacitor terminals for a few long moments. You can then hook up the probes for the meter and check to see whether the Ohms reading matches the reading on the side of the part. If the numbers differ, you will need a new capacitor.

You can simplify the capacitor checking process by calling in an HVAC tech to perform both the reading and the part replacement if needed. 

Overheating Condenser Coils

Your air conditioner has a safety shutoff that can happen if the system becomes overheated. The overheating usually arises from a problem in or around the condenser coils, which take in gas refrigerant from the compressor and then performs a phase change that makes the gas a liquid and makes the coils hot. A nearby fan is pointed at the coils to make sure the surface doesn't become overly hot.

The overheating shutdown can happen due to the condenser coils having a dirty surface, and this interferes with the phase change and can cause the coils to become hotter than the fan can offset. Or the fan itself can stop working, which will leave the coils with no way to reduce the phase-change heat.

You can stand near the condensing unit when it runs to listen to the sound of the fan running. If you don't hear the fan, shut off the unit manually and call in an HVAC tech for help. If you hear the fan, the problem is likely the coils. You want to leave the cleaning up to a pro because getting water where it doesn't belong in the condensing unit can cause even larger problems.