How can it damage an air-conditioner to run it when it is cold outside?

[PeterDonis]

Maybe there is a safety circuit to inhibit the compressor from running till the temperature is safe.

In cars, I don't think so; the low pressure cutoff is enough. When it's cold enough outside, the pressure of the refrigerant never gets higher than the low pressure cutoff, so the compressor won't run even if the A/C switch inside the car is turned on.

The problem with having an outside temperature sensor controlling this in a car is that such sensors can be skewed by the heat sources in the car itself, the main one being the engine, and by not having a good place available to sense undisturbed outside air.

 

[PeterDonis]

All heat pumps have a defrost mode

Doesn't that just use electric heat to warm the coils?

 

[PeterDonis]

Not only car A/C can work in the winter, but it is recommended to use them (It probably does it automatically anyway)

The compressor can't run if the low pressure cutoff stops it from running. In cold winter conditions, the refrigerant pressure inside the system will never get above the low pressure cutoff. Under those conditions, you can turn the "A/C" switch on inside the car, and have the light come on, and it won't make any difference; the compressor still won't run. If you know the sound of the compressor clutch engaging, try starting the car in cold weather, turning the A/C switch off to make sure it's disengaged, and then turning the A/C switch on again and listening for the sound of the clutch engaging. Under cold enough conditions, you won't hear it.

 

[Averagesupernova]

Concerning automotive A/C working in the winter, when the defrost is turned on it's not uncommon for the A/C compressor to run. Part of defrosting is to remove the moisture. Drive a vehicle long enough to get used to how well it defrosts and then when the A/C no longer works you will notice it does not defrost as well.

 

[russ_watters]

Doesn't that just use electric heat to warm the coils?

I think the typical method is to switch to AC mode briefly, but with the outdoor fan off:

https://www.hvac.com/expert-advice/heat-pump-defrost/

 

[jack action]

If you are familiar with them - how are the lubrication works for such an A/C unit in a car?

Oil to add if you replace the condenser, accumulator, receiver, or the evaporator​

Add the correct oil to the component before installing it into the system.

Component	Amount of oil to add
Condenser	1 Oz.
Evaporator	1.5-2 Oz.
Accumulator	2 Oz.
Receiver/Dryer	1 Oz.
Hose	1 Oz.

How much oil to add when replacing an AC compressor​

Most new AC compressors are filled with enough oil for the entire system. If you’re replacing all the components in your AC system or you’ve flushed the entire system, just install the new compressor and you’ll get good-to-go.

However, if you’re just replacing the compressor, you must remove some oil before installing it, or the system will have too much oil. Here’s how to adjust the oil in the compressor.

 

[sophiecentaur]

Part of defrosting is to remove the moisture.

In my old Skoda Octavia the windscreen will not clear well unless I use the AC . Trouble is that I only do short trips and the humidity in the cab is high due to trips to the dump with green waste. It's only a problem in the winter (leaves wetter then).

 

[Averagesupernova]

In my old Skoda Octavia the windscreen will not clear well unless I use the AC . Trouble is that I only do short trips and the humidity in the cab is high due to trips to the dump with green waste. It's only a problem in the winter (leaves wetter then).

I am not surprised you would have this trouble. A few extra people will cause the same thing.

 

[Averagesupernova]

I think the typical method is to switch to AC mode briefly, but with the outdoor fan off:

https://www.hvac.com/expert-advice/heat-pump-defrost/

My parents house has a heat pump with fuel oil backup. Defrost involves running the heat pump in A/C mode while running the oil burner. Pretty quick defrost cycle.
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My sister's house is set up the same except with electric resistance for backup heat. That one is not set up to run the resistance coils during defrost. Pretty sure the HVAC company could have done it but they didn't. My experience with them so-far has been less than stellar. I suspect they are simply not smart enough to handle with somewhat complex low voltage wiring for such a case.

 

[BillMcC]

TL;DR Summary: How can it damage an air-conditioner to run it when it is cold outside?

When I was inspecting the house that I later bought about ten years ago, it was the winter time. It was cold outside. I wanted to run the air-conditioner to test that it would cool the house off effectively, but my realtor asked me not to. She said that it would damage the air-conditioner to run it when it is cold outside. I asked her "how would it damage the air-conditioner to run it when it is cold outside?" She just told me "the air-conditioner is not made to run when it is cold outside." Well, duh. I knew that. But that does not answer the question.

Perhaps a residential air-conditioner would not cool the house as effectively in cold weather as in hot weather. But I cannot figure out why it would damage a residential air-conditioner to run it in cold weather. Maybe my realtor was misinformed.

How can it damage a residential air-conditioner to run it when it is cold outside?

I'm looking for a specific answer that tells me what parts of the air-conditioner would be damaged by running it in cold weather, and I am looking for information that tells me how exactly those parts would be damaged by running the air-conditioner in cold weather.

There were a lot of great replies here. Experts in the field often misunderstand this subject. There are many ways the cold can damage an outdoor unit. This subject is huge, and you have to know some of the mechanisms in the condenser for it to make sense.
Most AC systems sold in the north have a crankcase heater installed from the factory. It is an elemental heating element that runs when you power the unit. This is great as it keeps oil and refrigerant migration from taking place. Refrigerant migration takes place after an outdoor unit running in the cold shuts down after reaching the indoor setpoint. The indoor unit evaporator tends to run very cold when it is cold outside, and liquid refrigerant builds up in it until it shuts down and the refrigerant stops flowing. Then, the indoor evaporator coil warms up and forces liquid refrigerant into the low-pressure line. If the outdoor unit is physically located below the indoor unit, liquid can load up into the compressor if there is no crankcase heater. It can also fill the low-pressure or suction line, as it is sometimes referred to incorrectly in the field. Upon startup, this can slug(slang term) the compressor, which means introducing a large amount of refrigerant in liquid form into the compressor. This can cause the entire condensing unit to move around. It can rip out capacitors and undo wiring or rip the compressor from the condenser housing. It can even cause copper piping and brass service valve piping to break. Extremely funny to see. This happens if the AC power goes down at night while an outdoor unit is in heat pump mode. At this point, the crankcase heater is not functioning. So refrigerant can enter the compressor. Four hours later, when the power comes back on, the five-minute safety function that is designed to allow the pressure to equalize in the system in case there is a short ten-second power outage does not give the crankcase heater enough time to do its work. The condenser can do a dance, an actual dance. It's pretty funny to see. if you put a Hula hoop around it, it would keep the Hula hoop going. That is what it looks like.

 

[BillMcC]

TL;DR Summary: How can it damage an air-conditioner to run it when it is cold outside?

When I was inspecting the house that I later bought about ten years ago, it was the winter time. It was cold outside. I wanted to run the air-conditioner to test that it would cool the house off effectively, but my realtor asked me not to. She said that it would damage the air-conditioner to run it when it is cold outside. I asked her "how would it damage the air-conditioner to run it when it is cold outside?" She just told me "the air-conditioner is not made to run when it is cold outside." Well, duh. I knew that. But that does not answer the question.

Perhaps a residential air-conditioner would not cool the house as effectively in cold weather as in hot weather. But I cannot figure out why it would damage a residential air-conditioner to run it in cold weather. Maybe my realtor was misinformed.

How can it damage a residential air-conditioner to run it when it is cold outside?

I'm looking for a specific answer that tells me what parts of the air-conditioner would be damaged by running it in cold weather, and I am looking for information that tells me how exactly those parts would be damaged by running the air-conditioner in cold weather.

We always used to have a piece of cardboard from the last condenser we installed, especially for March startups, or for old York R-22 heat pumps to charge them in AC mode. You have to keep the discharge air of the outdoor condenser around 65 degrees or more. You just put the cardboard around the condenser. This way you do not stress the condenser fan.

 

[BillMcC]

My parents house has a heat pump with fuel oil backup. Defrost involves running the heat pump in A/C mode while running the oil burner. Pretty quick defrost cycle.
-
My sister's house is set up the same except with electric resistance for backup heat. That one is not set up to run the resistance coils during defrost. Pretty sure the HVAC company could have done it but they didn't. My experience with them so-far has been less than stellar. I suspect they are simply not smart enough to handle with somewhat complex low voltage wiring for such a case.

Some smart thermostats make it a simple choice while programming the t-stat, ecobee for example. Or if you have a zone control board, it is just a dip switch choice. You have to spend some time with the manuals to ensure each device is doing what you think it is doing or what it did last year. There is no time and money for that today. Things change so fast today, and there are no standards. They are trying to do away with the legacy wiring system and introduce a standard communicating system. The problem is that the companies making the new equipment never reached out to find out what was really needed in the field, so now we will have fancy, complicated stuff that still does not and cannot do the simple things customers ask for. We end up adding ice cube relays and designing the logic with them.

 

[PeterDonis]

Concerning automotive A/C working in the winter, when the defrost is turned on it's not uncommon for the A/C compressor to run.

Yes, as long as it's not so cold that the low side cutoff prevents it from running.

 

[PeterDonis]

I think the typical method is to switch to AC mode briefly, but with the outdoor fan off:

https://www.hvac.com/expert-advice/heat-pump-defrost/

Ah, that makes sense.

 

[BillMcC]

Some smart thermostats make it a simple choice while programming the t-stat, ecobee for example. Or if you have a zone control board, it is just a dip switch choice. You have to spend some time with the manuals to ensure each device is doing what you think it is doing or what it did last year. There is no time and money for that today. Things change so fast today, and there are no standards. They are trying to do away with the legacy wiring system and introduce a standard communicating system. The problem is that the companies making the new equipment never reached out to find out what was really needed in the field, so now we will have fancy, complicated stuff that still does not and cannot do the simple things customers ask for. We end up adding ice cube relays and designing the logic with them.

I think my realtor believed that if an air-conditioner ran in cool mode, it would actually physically damage the air-conditioner, not just not run effectively. What part of the air-conditioner would be damaged?

A lot of split systems run in the winter, especially when they serve an area with a lot of people that raise the temperature of the room to an uncomfortable level. There are a lot of ways to stop the compressor from getting damaged in low outdoor ambient conditions, adding a low-side accumulator, especially where long line set runs are involved. Adding a condenser fan control that monitors condenser temperature/pressure and shuts down the condenser fan when the pressure is low. This way, in conjunction with an accumulator, it can run even if the low side gets very cold and spills a little liquid into the low side piping. Almost all commercial freezers with condensers outdoors use this method to shut down at least one of two fans cooling the condenser.

Server room mini splits even have wind baffles that limit the amount of air that can blow through the condenser even though the fan is shut off by temperature pressure controls.