What Is the Coldest Temperature to Run an AC

About 60 degrees. That is the lowest outdoor temperature recommended for using AC. And trying to get your air conditioner to cool your home to lower than that temperature can cause damage to the system. 

When most people think of running their air conditioners, they generally think of only running it when the weather is hot and/or humid.

However, some homeowners for various reasons run their air conditioning when it is cool outdoors. 

Read on to find out more about how cold it can be to run your air conditioner in cooler weather conditions. 

Running AC Below 60 Degrees

Running an air conditioner when the temperature is below 60 degrees is never recommended. To put it more bluntly, it is a bad idea. 

Most air conditioner manufacturers state this in their literature that the AC should not be run when the ambient temperature is 60F or below. By the way, ambient temperature is a technical phrase referring to the temperature in which the compressor and coil are functioning – that is, the outside temperature. 

Why Running AC Below 60 Degrees is a Bad Idea 

There are three main reasons why you should never operate an air conditioner in cooler weather.  

1). First of all, the lubricant in an AC compressor is designed for warmer temperatures. When the temperature is below 60 degrees, the lubricant thickens and might not do its job. Imagine your car engine without motor oil or oil that wasn’t fully lubricating the pistons as they traveled up and down in the cylinder. That would be bad news.

If you turn down the AC in cool temperatures, the thick lube will cause it to run inefficiently, create more wear and tear and potentially cause mechanical failure.

2). Secondly, many air conditioners have a cold weather sensor. If the temperature is too cold, the sensor will not allow your air conditioner to kick on. Older air conditioners lack the cold temperature sensor, so they can turn on and cool the home, but this will possibly damage the AC unit. 

3). Even if the AC runs OK and starts removing heat from your home, pretty soon the cooling coil will freeze up. This will cause the compressor to work too hard. And that could cause irreparable damage to the air conditioning system. 

4). Finally, a word of caution from Oklahoma home inspector C. Bottger: In cold temperatures, there is a risk the refrigerant won’t completely vaporize as it should. The result will be it flowing back to the compressor in a liquid state – and that’s another source of compressor damage, primarily to the valves when the unit starts. This is known as liquid migration. 

Running AC Under 65 Degrees

While 60 degrees and below is a standard temperature that is too cold to run an air conditioner, running an AC unit at 65 degrees or cooler is also not recommended. 

The potential problems are the same as those listed above – thick lubricant causing the compressor to wear unnecessarily, potential coil freeze-up and liquid refrigerant (freon) flowing into the compressor and causing damage. 

The general rule recommended by AC pros including those here at Pick HVAC is to wait until the outside temperature is at least 68 degrees Fahrenheit to operate your air conditioning system. If it is 65 degrees or cooler outside and you are too hot inside your home, open a window or turn on a fan. Or both. 

Running AC When It’s Colder Outside than Inside

Homeowners should not run their air conditioners when the temperature outside is colder than the temperature inside. 

Running AC when it’s colder outside than inside is a bad idea because air conditioners are not constructed to operate effectively and efficiently in cold weather, as we’ve attempted to make clear above – that is, that running an air conditioner in cold weather could damage it.

As noted earlier, older units don’t have a sensor to protect the AC by preventing it from running in cold ambient temperature, so they will operate whenever they are turned on. And if your AC is older, the next breakdown might be the end of the unit. 

Minimum Outside Temperature For Air Conditioner

The minimum outside temperature to run an air conditioner is 60 degrees, according to most manufacturers. But even running it when it is 60F outside might not be a good idea.

When you talk with technicians that work on ACs and heat pumps every day, they usually say that you shouldn’t run air conditioning when it is 65 or below outside. Some put the temperature as high as 70.   

Can a Heat Pump Run below 60 Degrees When Cooling?

Like a central air conditioning system, heat pumps should not run in AC Mode when the temperature is below 60 degrees. Heat pumps are designed to produce cool air that is 15 to 20 degrees cooler than the outside temperature. 

Will Running an Air Conditioner in Cold Weather Damage It? 

The answer to the question, “Will running an air conditioner in cold weather damage it?” is a definite yes. 

We hope it has become clear that air conditioners are not designed to operate in cold weather. Running AC under 65 degrees can cause damage to the air. Let’s review one more time the potential dangers of running air conditioning in temperatures below 65F – and for sure below 60 degrees Fahrenheit.

1). Thick lubricating oil doesn’t do its job, and the compressor wears out quickly.

2). The indoor coil will freeze up, which will prevent it from working and could cause the compressor to become overworked and overheated – both can damage it.

3). Non-vapor refrigerant (liquid refrigerant) in the compressor can damage its valves on start up. 

Final Note – The compressor is the most significant and expensive component of a central AC condensing unit – the outside unit.The cost of compressor replacement is $1,300 to $2,500 – and possibly higher now that prices for parts and labor have gone up. That’s a big bill, so the minimum outside temperature air conditioner should be run is 65 degrees to give your compressor the TLC it needs.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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