---
title: "True/false: air conditioner is closed loop"
subject: "Control Systems"
chapter: 1
key: "semester_3/control_systems:tf-air-conditioning-closed"
source: https://www.bctengineer.com/q/semester_3/control_systems/tf-air-conditioning-closed
site: BCT Engineering
---

# True/false: air conditioner is closed loop

Control Systems · Chapter 1: Control System Background

- Asked in: 2078 Bhadra, 4 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/control_systems/tf-air-conditioning-closed
- Whole chapter: https://www.bctengineer.com/md/semester_3/control_systems/chapter-1

## Question

State whether the following statement is true or false and justify: An air conditioning system is an example of closed loop control system.

## Short answer

True. An air conditioner with a thermostat is closed-loop because the room temperature is measured and compared to the setpoint, and the error controls the compressor. The output affects the control action, which is the defining feature of closed-loop control.

## Answer

**True.** An air-conditioning system with a thermostat is a closed-loop control system, because the room temperature (output) is measured and compared with the set temperature, and the difference decides whether the compressor runs.

```text
 set   +  e  +----------+  +----------+  +------+ temp
 ----->(Σ)-->|Thermostat|->|Compressor|->| Room |-+->
        ^ -  +----------+  +----------+  +------+ |
        |                                         |
        +--------[Temperature sensor]<------------+
```

- **Reference:** set temperature, e.g. 24 °C.
- **Sensor:** a thermistor in the indoor unit measures the room temperature.
- **Controller:** compares the two and switches the compressor on/off, or varies its speed in an inverter AC.
- **Plant:** the room; **disturbances:** sunlight, people, opening doors.

If the room becomes warmer than 24 °C, an error appears (room temperature above the set value) and cooling increases; when the set value is reached, the compressor slows or stops. The output itself affects the control action, which is the defining feature of a closed loop.

Note: an old cooler or fan that runs at a fixed setting without a thermostat would be open loop.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. An air conditioner with a thermostat is
   A. Open loop
   B. Closed loop
   C. Neither
   D. Linear time-varying only
   Answer: B. Room temperature is measured and compared with the set value, so it is closed loop. (Key point: True or false)

2. What defines a closed loop in the air conditioner?
   A. Output temperature affects the control action
   B. The compressor runs for fixed time
   C. No sensor is used
   D. Set temperature is ignored
   Answer: A. The output itself affects the control action. (Key point: Defining feature)

3. Which is a disturbance for the AC loop?
   A. Set temperature
   B. Sunlight, people or opening doors
   C. Thermostat comparator
   D. Compressor
   Answer: B. These unwanted inputs change room temperature. (Key point: Disturbances)

4. Which device would be open loop?
   A. An old fan running at a fixed setting without thermostat
   B. An inverter AC
   C. A thermostat heater
   D. A geyser
   Answer: A. A fixed-setting device does not use output information. (Key point: Open-loop counterpart)

## Related in Control Systems

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- [Control system block diagram and closed loop advantages](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Awhat-is-cs-bd-cl-advantages) — Control Systems, chapter 1
- [Control system importance and closed loop components](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Adefine-cs-importance-components) — Control Systems, chapter 1
- [Why closed loop response is faster than open loop](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Acl-faster-than-ol) — Control Systems, chapter 1, asked 4×
- [LTI system and closed loop in modern systems](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Alti-define-cl-pronounced) — Control Systems, chapter 1

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