Correct, parent comment is confused. UPS hires many seasonal employees, and even pays higher wages during the holiday season to all workers (Union and seasonal). After the holidays if the facility has need for more workers, some of the seasonal workers are offered permanent employment, after which time they become part of the Union.
It's not seasonal at all and HVAC shops are far more comprehensive than just Heating/Cooling. V is for ventilation so any ventilation system consisting of blowers, fans and ducting is included. Air Conditioning is understood to be cooling but those systems range from window units to massive chiller systems. They can also service refrigeration systems for commercial and industrial use.
At work we had an out of warranty water chiller for a laser break down so we called our HVAC guys who found the leak, patched it and recharged the system same day.