Is it safe to run the air conditioning when it is cold outside?
No, you should not operate the cooling system when the outdoor temperature is below 50°F (10°C). Running the air conditioning compressor in cold outdoor temperatures can cause equipment damage. This is listed as a Caution warning in the manual. (Page 6)
From the official Honeywell TH5110D Home Programmable Thermostat manual, page 6
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