There are a lot of variables in this conversation: if you need to ask this question, you should probably go with the 60° rule of thumb.
Heat pumps have an accumulator, air conditioners do not. The accumulator stores refrigerant that would otherwise flood back on the compressor under low ambient conditions. It also collects the oil that was flushed out of the compressor on a cold startup, so it can be returned at a slower rate through a small orifice at the bottom of the accumulator.
It depends on the type of compressor you have. Scroll compressor can handle testing at any condition as long as you don’t run it the entire time you’re on your inspection in the wintertime.
As for the question of wide variations of ambient temperature before testing: if the duration of cold weather has been a long time since it was last run, or if the compressor doesn’t have a heater, you should leave it alone. The heater can be a belly band or an immersion heater in the crankcase of the compressor, which keeps the refrigerant from being absorbed into the compressor oil. If it was just cold last night, you’re fine running it. Recommend that you turn on the heater and raise the temperature in the house and test that first. Then you have a significant load for a short period of time that will help prevent any liquid slugging of the refrigerant on the compressor.
As for air conditioners with accumulators: I know of no reason to have an accumulator on a unit less than 25 years old because most of the compressors younger than 25 have scroll compressors which can handle anything without the need of an accumulator. Maybe something in your regional area.
Mark; a split system is a two-part system, not just an air conditioner. Both heat pumps and air-conditioners can be split systems, otherwise they are a package unit.
Note: when you say “run the unit”, just how long is that?
Hopefully nobody tries to lower the air temperature in the building during the wintertime! All you have to do is bump the unit and see if the fans and compressor run, you don’t need to take any dam delta-t at the registers with your IR thermometer! If you are doing this, even at 60° with no load in the house, you can damage the compressor on an air conditioner. All it takes is a dirty filter or dirty evaporator coil, and you will slug the compressor. The key here is indoor ambient temperatures. That is the load that causes the refrigerant to change state. No load, no change of state, compressor slugging will occur. If The heat is not on in a vacant house and it was really cold the previous night, it is most likely that the indoor air temperature is below thermostat set point and therefore no load.
There are air-conditioners, primarily in commercial settings that have low ambient controls on them which turns off the outdoor fan and prevents the drop of refrigeration pressures, thus temperature in the system.These systems can be run anytime. They have been designed to do so. Depending on your geographical location, you may or may not see them in a residential setting. Also variable speed units (units that have fan and compressor speed control) can also be run.