Understanding the Thermostat Location in Window AC

The thermostat is a crucial component in a window type air conditioner. Its main function is to sense the room temperature and control the operation of the compressor to maintain the desired temperature set by the user. Understanding where it's located within the electrical circuit helps explain how the AC system regulates cooling.

Role of the Thermostat in the AC Circuit

In a window air conditioner, the electrical circuit controls various components like the compressor, fan motor, and potentially heaters (in reverse cycle units). The thermostat acts as a temperature-controlled switch within this circuit. When the room temperature rises above the set point, the thermostat closes its contacts, allowing power to flow to the compressor circuit. When the room temperature drops below the set point, the thermostat opens its contacts, stopping the compressor.

Analyzing the Location of the Thermostat

Let's look at the common components involved in controlling the compressor and where the thermostat fits in.

• Selector Switch: This is the main switch where the user selects the mode (Cool, Fan, Heat, etc.) and fan speed. It directs power to different parts of the circuit based on the user's selection.
• Overload Protector (OLP): This is a safety device, typically integrated with or connected to the compressor motor. It monitors the motor's current and temperature. If the motor draws excessive current or overheats, the OLP opens the circuit to protect the motor from damage.
• Relay: A relay is often used as a high-current switch controlled by a low-current signal. In AC units, a relay might be used to switch the main power supply to the compressor motor, controlled by the thermostat and selector switch signals.
• Running Winding & Winding: These are parts of the electric motor, typically the compressor motor or fan motor. They are the loads that consume power, not control devices in the circuit path of the thermostat signal itself.
• Condenser Fan: This motor drives the fan that blows air over the condenser coil, part of the refrigeration cycle. It operates when the system is cooling, usually in parallel with the compressor or controlled by the same circuit, but the thermostat's primary control is over the cooling capacity via the compressor.

The thermostat's signal needs to be in line with the user's selection (from the selector switch) and before the final power switching to the compressor, which is often handled by a relay, but it must also work in conjunction with safety devices like the OLP.

The thermostat typically receives power after the selector switch has confirmed a "cooling" mode is selected. Its output signal then influences the circuit that powers the compressor. The OLP is directly in series with the compressor motor's power supply to immediately cut power in case of an overload. Therefore, the control signal path from the selector switch often goes through the thermostat (which decides *if* cooling is needed) before potentially activating a relay that powers the compressor circuit, where the OLP provides the final safety cut-off.

Considering the options, the thermostat is positioned in the control circuit path originating from the selector switch, influencing the signal that eventually leads to the compressor circuit which is protected by the OLP. This places it logically in the signal flow between the selector switch's output for cooling mode and the control path leading towards the compressor circuit guarded by the OLP.

Based on how these components interact in a typical window AC control circuit, the thermostat is strategically placed in the signal path that originates from the user's selection via the selector switch and governs the activation of the compressor circuit which includes the OLP for safety.

Why Other Options Are Less Likely

• Relay and OLP: The thermostat typically controls the relay coil which then switches power to the compressor (in series with the OLP). So, the thermostat is usually influencing the relay, not placed *between* the relay and OLP in the power path. The OLP is in the main power path *after* the relay contacts and *before* the motor winding.
• Running winding and Condenser fan: Both are loads (motors). The thermostat is a control device that governs when these loads receive power, it's not placed electrically between them.
• Relay and Winding: Similar to the previous point, the winding is part of the motor load. The thermostat controls the signal that activates the relay, which then supplies power to the winding (often via the OLP). The thermostat is not positioned between the relay (specifically the contacts) and the motor winding itself.

Therefore, the placement that makes the most sense functionally within the control circuit, influencing the activation signal coming from the selector switch and working in conjunction with the final power path protected by the OLP, is between the selector switch and the control circuit elements leading to the compressor (which includes the OLP).

Revision Table: Window AC Components

Additional Information: Types of Thermostats

Thermostats in air conditioners can be:

• Mechanical Thermostats: Use a bimetallic strip or bellows that expand/contract with temperature changes to open or close electrical contacts.
• Electronic Thermostats: Use thermistors or other electronic temperature sensors to measure temperature and a microcontroller to control relays or triacs to switch power. These are more precise and allow for digital displays and programming.

Regardless of the type, the functional placement within the control circuit for regulating the compressor based on room temperature remains similar in principle.