Our SOP states that we should not run an air conditioner when the air temp is below 60F because it could cause damage. Can anyone explain what kind of damage can occur?
I think you meant to say 65° Fahrenheit!
- operate equipment or systems if the exterior temperature is below 65° Fahrenheit, or when other circumstances are not conducive to safe operation or may damage the equipment.
As a result of liquid migration the refrigerant in a closed loop system migrates to the coldest area of the system which when below 60 degrees or what ever your SOP dictates is the exterior condenser the liquid refrigerant has the capability of entering the oil sump of the compressor and when the unit is activated the liquid refrigerant and the oil can be pumped through the discharge valves of the compressor and create damage as the valves within the compressor are designed to pump vapor not liquid. These type of valves are not used on a scroll type compressors there are no valves to damage. Thus the only possible damage than can occur to a scroll compressor is if the oil is pumped out of its reservoir and does not readily return to the reservoir which is highly unlikely unless the the line set between the A-coil and the exterior condenser is lengthy or the A-coil is located within a basement below the exterior condensing unit
Couldn’t have said that any better Charley. 
Merry Christmas to you. 
Thanks Charley,
I needed to explain the reason for not testing under 65 to a client.
This helps a lot.
Also yesterday when we went to church, it was very mild here, about 40 degrees The church was packed & the air condioners were running full blast.
Do you think they may have been damaged?
Roy
Here’s more info at recent discussion.
I would bet my red hat that the units in your Church were not damaged. Most units but not all on a church are set up with colder weather operation. Crankcase heaters and suction line accumulators and possible oil separators on the discharge line.
To many HI’s are under the impression that if one operates the unit below 60 degrees F. that the unit is going to disappear in a cloud of smoke. All they under stand is what is written in a book. I can state after 40 years of operating thousands of residential units and some at 10 degrees F I have never damaged one
I think Mr. cmi meant to say: to type the “degree” symbol, on a Mac it’s shift+option+8 and on a PC it’s Alt+0176.
I have seen 60 degrees Fahrenheit to Kevin.
I questioned it myself and saw it referenced several times 2 weeks ago.
To be on the safe side Kevin I state my standards of safe operational practices is 6o degrees Fahrenheit to my clients.
Also explaining that 65 degrees is also referenced in some literature.
That it will be noted in limitations and that I will inspect the system when the ambient temperature rises above 65 for free.
JMO
Great explanation Mr. Bottger.
Text book.
In the vault it goes.
Thanks Linus!
When the temp outside is too cold the pressure in the condenser (outside section) is very low. In addition usually there is not a enough heat load on the evaporator (inside section) this causes a low pressure there as well. The combinatioin of low pressure in the inside coil and outside coil will not let the refrigerant in the evaporator completely turn into a vapor. if you get liquid refrigerant back to the compressor it slugs through the compressor valves damaging them and it washes the oil out of the compressor as well causing lack of lubrication. we all know what happens when you don’t have oil in a car engine.
Kenneth.
Look at post #3.
I think it is an excellent narrative about refrigerant and low temperature operations.
You are doing a better job then myself at the moment in understanding then creating a narrative for the condition.
Mr. Bottger explanation should influence you.
Good for you Mr. Levine.
I just tell them the oil is too thick and cold,may damage the compressor, and I don’t want to buy a new one.
But I like Charlie’s explanation.