How can you check the heater on the air dryer for voltage?

To check the heater on the air dryer for voltage, it is essential to ensure that the system is energized and operational. Measuring for voltage requires that the ignition switch is in the ON position, as this allows electrical power to flow to the heater circuit. By removing the plug and directly using a voltmeter to check for voltage across the terminals with the key ON, you confirm that the heater is receiving the proper electrical supply needed for it to function correctly.

This method is particularly important in diagnosing air dryer issues, as it quickly indicates whether the heater is receiving power or if there’s an interruption in the circuit. Other options, while they might provide some information, would not effectively determine if voltage is present at the heater terminations when needed. For example, measuring resistance across the terminals without power does not indicate whether the heater can actually operate under normal conditions. Inspecting for physical damage can show visible issues but won't confirm electrical functionality. Testing with the key OFF would not provide any voltage reading, making it ineffective for this purpose.