Chill with Confidence: Ace the 2025 ASE Air Conditioner Exam and Keep Cool Under the Hood!

To measure the voltage at the compressor clutch, it is essential for the engine to be running, the key to be in the on position, and the air conditioning set to a cold position. This configuration allows the air conditioning system to be in an operational state, which is necessary for engaging the compressor clutch.

When the engine is running, it provides the requisite power for the system to operate, and setting the AC to a cold position initiates the cooling process and engages the compressor. This engagement is what allows for the measurement of voltage across the clutch. It ensures that the compressor is actively being commanded to engage, allowing the technician to verify the voltage being delivered to the clutch under normal operating conditions.

The other choices do not provide the right conditions for accurately measuring the voltage at the compressor clutch. When the engine is off or the key is off, there is no power to the system, and thus no voltage can be measured. Similarly, placing the vehicle in service mode or disconnecting the battery would also prevent any voltage measurement while the system is not operational. Therefore, having the engine running, the key on, and the AC set to cold is the correct approach for measuring voltage at the compressor clutch.