The A/C has components like the blower motor, which are vital to its operation. The blower motor helps move air through the HVAC (Heating, Ventilation, and Air Conditioning) system. This component is part of the electrical system and has various wires and connectors around it.

The blower motor wires will overheat when using the heater while the cabin air filters are restricted. The air filters can become clogged with dirt, especially if they're too old. Then, the overheating will burn nearby plastic components, causing a smell through the heater and A/C system.

A humming noise escapes from the engine bay, varying depending on the vehicle and engine's speed. In this case, the sound only appears when you use either the air conditioning or defrost system.

The radiator keeps your engine cool by removing heat from the coolant through airflow. The coolant flows inside the radiator, and air flows over the outside fins, transferring heat away. Any restriction in the air or coolant flow makes it harder for the radiator to remove heat from the coolant. Consequentially, your engine overheats.

If you notice the heater malfunctioning, A/C malfunction, pinging sounds coming from the engine, red check engine light, gurgling noises from the engine/dashboard, and steam coming from the hood, save this information; they're essential if you go to an auto shop later.

The expansion valve is a device that helps regulate the flow of a substance called "freon" in an air conditioning system. The valve works by reducing the pressure of the freon. This causes the freon to change from a liquid to a gas, which helps it absorb heat and make the air colder.

However, the part of the valve that controls how much freon flows through can wear out or break. This can cause the valve to malfunction and make the air coming out of the air conditioner shift temperature quickly, constantly feeling warmer and cooler.

Some cars have computers that modernize their performance. For example, the computer can turn off car parts that might make the engine overheat. So, if the air conditioner is on and the engine is overheating, the computer turns off the air conditioner before the heat gets extreme. This safety behavior prevents the engine from overheating and causing damage. But it does make the temperature light flash on the dashboard.

In an air conditioning system, an orifice tube helps turn a liquid substance called freon into a gas. This part helps the system absorb heat and cool the air. The tube has a screen to keep external particles out, but if something significant goes wrong inside the air conditioning system, like a part breaking, those particles can get through and block the orifice. This can cause the air conditioning system to stop working correctly and even shut down to protect itself. Hence, the air might start cold and then heat over time.

A leak in the air conditioning system can cause water to enter it. When the freon passes through the expansion valve, there is a rapid drop in pressure and temperature. If there is any water in the freon, it can freeze at the orifice of the expansion valve and block it. This can cause the air coming out of the air vents in the vehicle to become very cold until the orifice is completely blocked with ice. As a result of the blockage, the compressor shuts off due to the high-pressure safety switch being triggered by accumulated pressure. When this happens, the temperature in the vehicle rises to the outside temperature. It takes significant time for the expansion valve to thaw and for the AC system to start working again.

The condenser is a part of the air conditioning system that sits before the radiator. Its job is to help remove heat from the freon and coolant by allowing air to flow across it. When the cooling fan turns on, it helps pull this air through the condenser and radiator to cool everything down. However, if it fails, it can diminish airflow. The AC and engine temperature can rise and cause problems if there isn't enough airflow.

Your car's air conditioning system has several doors in its box that merges hot and cold air and direct it to where it must go. The Mode door motor is usually connected to a lever mechanism that controls multiple doors. However, if the Mode door motor gets miscalibrated, it causes air to come out of the wrong vent or not come out at all. This happens due to an intermittent connection that causes the motor to function only sometimes or stall, directing air to the wrong location.

The evaporative temperature sensor is a small but essential part of your car's air conditioning system. It's located in the airbox before the evaporator core, and it determines the core's temperature. This information is crucial for maintaining your AC system's efficiency. Another essential function of the temperature sensor is to alert the climate control module if the evaporator freezes over. If the sensor registers a temperature colder than the actual temperature of the evaporator, the climate control module thinks that the evaporator is frozen. This causes the AC system to shut down until the temperature rises.

These symptoms can be caused by a faulty "belt-like" rubber component known as a serpentine — or accessory — belt. This component moves between gears and pulleys in the engine, providing power for systems like the A/C compressor, radio, water pumps, power steering, alternator, and lights.

So, if you're noticing an issue with any of these accessories/systems while also picking on a burning smell, explain this to a mechanic.

The burning rubber smell happens in this case because this belt can degrade, damaging some pulleys' bearings, loosening itself, and touching hot parts. Sometimes, the spring-loaded tensioners might be underperforming, causing the belt's looseness.