Why the compressor engage on a 2001 4Runner when AC button is pressed?

When the AC button is pressed in a 2001 4Runner, the compressor engages to initiate the process of cooling the vehicle's interior. Here's a step-by-step explanation of what happens when the AC is turned on:

1. AC Button Press: When you press the AC button on the vehicle's dashboard, you are essentially sending a signal to the climate control system.

2. Signal to AC Control Module: The AC button sends an electrical signal to the AC control module (sometimes called the HVAC module). This module is responsible for controlling various aspects of the climate control system, including the operation of the compressor.

3. Compressor Engagement: Upon receiving the signal from the AC control module, the compressor clutch is activated. This engagement is typically accompanied by a noticeable clicking sound.

4. Refrigerant Flow: With the compressor engaged, it initiates the refrigerant flow in the air conditioning system. The refrigerant is a crucial component that absorbs heat and undergoes phase changes (liquid to gas and back) during the cooling process.

5. Cooling Process: As the refrigerant circulates through the system, it absorbs heat from the vehicle's interior. The warm refrigerant then passes through the condenser (located in front of the radiator), where it is cooled down by ambient air.

6. Expansion and Evaporation: The cooled refrigerant, now in liquid form, flows into the expansion valve (or orifice tube), where it undergoes rapid expansion. This expansion causes the refrigerant to convert into a low-pressure gas and absorb more heat. The evaporator (located behind the dashboard) facilitates this process.

7. Blower Fan: Simultaneously, the blower fan inside the vehicle is turned on. This fan circulates the cooled air within the cabin, removing the warm air and replacing it with the cooler air.

8. Continuous Regulation: The AC control module constantly monitors the temperature and adjusts the operation of the compressor, blower fan, and other system components to maintain the desired cabin temperature.

So, when you press the AC button in your 2001 4Runner, the compressor engages to initiate the refrigerant flow and cooling process. The combination of compressor activation, refrigerant circulation, and air circulation results in the cooling of the vehicle's interior.