What is the first step in troubleshooting an HVAC unit that is not cooling?

When troubleshooting an HVAC unit that is not cooling, one of the most crucial initial steps is to check the thermostat settings. The thermostat is the control center of the HVAC system, dictating when the system should turn on and off based on the desired temperature set by the user. If the thermostat is set incorrectly, whether it’s set to a temperature higher than the current room temperature or if it is inadvertently placed in a mode other than cooling (such as the 'off' or 'heating' mode), this can prevent the system from operating as expected.

Ensuring the thermostat is set to the cooling mode and at a temperature lower than the current room temperature is fundamental in identifying whether the issue lies within the operating parameters of the HVAC system itself or if it is merely a matter of incorrect settings. This quick check can save time in the troubleshooting process and help pinpoint the cause of the cooling issue more efficiently.

While examining other factors such as the air filters, power supply, or refrigerant levels are also important in the overall diagnostic process, confirming the thermostat settings is often the simplest and most immediate action that can lead to restoring function to the cooling system.