The first thing to do whenever servicing any HVAC equipment is to look at the rating tag and verify the unit operating voltage. Then check for that voltage where the power enters the unit. Often times a serviceman will call with an issue, and when asked about power, the answer they give is “I have power to the unit.”
Some service techs have a bad habit of checking power from the line to the ground and not from the actual two power lines coming into the unit. If you have a 208/230 volt single phase unit and the contactor is pulled in or a crank case heater is installed and you have one dead leg of power, you will read 115v to ground on each leg due to a back feed through the unit, but you will not have 208/230.
So remember to verify the proper voltage first! A digital multimeter is a good tool to have handy.