if the switch is closed then voltage if it exists would go to HVAC - you could test for voltage at the HVAC as well - If the HVAC does not have voltage then if you open the disconnect is would not have voltage as well. Would you need clearances for a wall switch? it can be considered a non fused disconnect in certain uses. Likely is the term usedTesting voltage to an HVAC unit. You could accidently short it.
but not clearances - turn off / lock off the breaker- no need to checkThere is still power in the switch in the off condition. PPE is required to verify the absence of voltage.
Still need to verify absence of voltage somewhere if you are doing electrical work.but not clearances - turn off / lock off the breaker- no need to check