Testing HVAC if Temperture is below 60 degrees

[David Nasser]

I have verbiage that states that the outside temperature is to low
to test AC system. ( to turn on from the thermostat) Does anybody
know the reasoning behind that disclosure ?

David

[David A. Andersen]

A/C (not heat pumps) are not set up to run in cold temps.

1. They do not have wide ranging metering devices. They also do not have an accumulator to catch liquid refrigerant before it makes it to the compressor (like a HP does).
2. There is no load indoors to use up the liquid refrigerant. It is also cold outside so low head pressure causes the system to starve.
3. They don't have an immersion heater in the compressor.The refrigerant migrates into the oil when cold outdoors a not used for a while. At startup the refrigerant (and the oil with it) is pumped out of the compressor. Oil may damage the compressor.

For a compressor to be efficient, there must be little clearance between the compressor piston and the head. Any liquid getting in there will break a valve or crankshaft.

If you do run it in the cold, It wont run right for you to tell anything but that it runs.

It can be modified to operate in the cold (by an HVAC engineer) so it can be tested, but you can't.

[David Nasser]

Originally Posted by dandersen

A/C (not heat pumps) are not set up to run in cold temps.

1. They do not have wide ranging metering devices. They also do not have an accumulator to catch liquid refrigerant before it makes it to the compressor (like a HP does).
2. There is no load indoors to use up the liquid refrigerant. It is also cold outside so low head pressure causes the system to starve.
3. They don't have an immersion heater in the compressor.The refrigerant migrates into the oil when cold outdoors a not used for a while. At startup the refrigerant (and the oil with it) is pumped out of the compressor. Oil may damage the compressor.

For a compressor to be efficient, there must be little clearance between the compressor piston and the head. Any liquid getting in there will break a valve or crankshaft.

If you do run it in the cold, It wont run right for you to tell anything but that it runs.

It can be modified to operate in the cold (by an HVAC engineer) so it can be tested, but you can't.

Thanks

[David A. Andersen]

Hope that helped.

Had to be brief, leaving for work...

[Wade Williamson]

Thanks for the very detailed explanation. I have had the same question.