Recently, BHPian Jeroen shared an insightful experience with the community, and it sparked an idea. Inspired by the detailed discussions on car AC systems within enthusiast forums, particularly focusing on the intricacies of car AC systems, I decided to delve into a practical exploration.
Having previously worked on the air conditioning in my Jeep Cherokee and my wife’s Ford Fiesta, documented in my personal car tinkering thread, I gained hands-on experience with AC systems. Just recently, with the help of my neighbor Jack, an AC specialist, we replaced the AC compressor on the Fiesta. This presented a perfect opportunity to dissect the old compressor and understand its inner workings.
My fascination with taking things apart dates back to childhood. While my early attempts sometimes resulted in parental interventions – like the time I dismantled our central heating furnace – I’ve since become more adept at reassembly, usually managing to put things back together successfully.
My aim with this compressor teardown is twofold. Firstly, to gain a comprehensive understanding of its internal components and operation. Secondly, with a long-term vision, I’m considering transforming it into a ‘cut-away’ display model – a cool addition to my garage and a visual aid for understanding car AC systems.
So, join me as we dismantle this compressor piece by piece. This exploration will be somewhat technical, possibly even nerdy, but primarily mechanical, making it accessible to most enthusiasts interested in car air conditioner parts.
Before we dive into the compressor itself, let’s briefly recap how a car AC system functions. For a detailed explanation, numerous resources are available, but here’s a simplified overview using the diagram below.
The compressor, the heart of the system and our main focus, is responsible for compressing the refrigerant. This high-pressure refrigerant is then pushed towards the evaporator. The evaporator, typically located behind the dashboard and integrated within the car’s air circulation system (as detailed in my Jeep AC work), cools the air.
This cooling process occurs because the expansion valve regulates refrigerant flow based on upstream temperature. From the evaporator, the refrigerant passes through a dryer to remove moisture and then reaches the condenser. The condenser, usually positioned at the front of the car, dissipates heat, completing the cycle.
While this is a simplified explanation, it covers the core principles of a car AC system. Modern car AC systems, however, incorporate sophisticated controls and sensors. These include internal and external temperature sensors, sun load sensors (that small dome on your dashboard), and various pressure and temperature sensors throughout the system.
The functional diagram of the Ford Fiesta AC system, largely unchanged since 2012 and likely still relevant in more recent models, illustrates this complexity.
Ford Fiesta AC system functional diagram
Car AC compressors come in various designs, primarily differing in their control mechanisms: clutch systems, variable displacement mechanisms, or a combination of both.
Clutch-only compressors are typically found in older vehicles, like my Jeep and Alfa Romeo Spider. These systems are ON/OFF, engaging and disengaging the compressor via a clutch based on system pressure. A distinct “click” sound is usually audible when the clutch engages. The clutch cycles on and off frequently, typically in intervals of 20-60 seconds, depending on system demands.
Variable displacement compressors, like the one in the Fiesta, offer more nuanced control. These compressors run continuously once the engine is started, but they regulate the volume of refrigerant pumped. This continuous operation, however, can lead to wear and a slight drain on engine power, impacting fuel efficiency, even when the AC isn’t actively cooling.
Early variable compressors sometimes suffered from durability issues when not used frequently, as lack of pumping could hinder lubrication. Refrigerant also plays a crucial role in circulating oil throughout the system.
To address these issues, clutch-variable compressors have become increasingly common, combining the benefits of both types.
Here’s a side-by-side view of the old and new compressors. The silver one is the new compressor installed in the Fiesta, and the black one is the old unit we’re about to dissect.
The prominent black pulley at the front houses the clutch. An electrical connector is visible, used to energize the electromagnet that engages the clutch.
On the bottom, another black connector sits atop the compressor housing, directly on the control valve of the variable displacement mechanism, which we’ll examine later.
When installing a new compressor, it’s crucial to determine if it’s pre-filled with oil. Car AC systems require a precise amount of lubrication oil. If the compressor is already oiled, less needs to be added during system recharge. Recharging involves adding refrigerant along with the correct oil quantity and a UV dye for leak detection.
Workshop manuals specify the oil capacity for the entire system and individual components (compressor, dryer, evaporator, etc.). This information is essential when replacing components to ensure proper oil levels are maintained.
Checking the compressor’s model plate is always a good practice. This original Ford Motor Company compressor, manufactured in Hungary in 2015, is designed for R134A refrigerant, a common type in modern car AC systems.
Let’s take a closer look at the clutch mechanism at the front of the pulley.
The electrical lead connects to the electromagnet, which is responsible for engaging the clutch.
To remove the pulley and clutch, the small bolt on the shaft needs to be unscrewed. To hold the pulley securely, I used a vise and a small socket to loosen the nut.
Here’s the inside of the clutch plate. When the electromagnet is energized, it pulls this plate towards the pulley, directly engaging it. Notice the bearing in the center of the pulley. When the clutch is disengaged, the pulley spins freely, driven by a V-belt, similar to the alternator, while the compressor remains idle.
The clutch plate’s center has splines that mate with corresponding splines on the compressor shaft, directly linking the clutch to the compressor shaft. The pulley freewheels on the shaft until the clutch engages.
This is the clutch plate viewed from above. It consists of the main clutch plate with a spring attached to a smaller plate. When the electromagnet de-energizes, the spring pulls the clutch plate away from the pulley, creating a small gap – a gap that can indicate clutch wear. On my Jeep, I’ve replaced the bearing, and on a previous Jeep, I had to replace the entire clutch due to wear, as thinning of the clutch plate can prevent the electromagnet from engaging it effectively.
Arranged from right to left, you can see the components as they were removed: the bolt and washer, the clutch plate, a circlip securing the pulley bearing, the pulley with the bearing still inside, and the rest of the compressor with the exposed electromagnet on the right.
Common wear points in these compressors are the bearing and the clutch. Even when the AC isn’t in use, the pulley is still rotating, leading to wear over time. In my experience with AC repairs, bearing wear is more frequent, followed by clutch wear (excluding refrigerant-related issues). Fortunately, replacing the clutch or bearing is usually straightforward on most compressors, often possible without removing the compressor from the car and without needing to evacuate the refrigerant. Refer to the links at the end of this post for my Jeep AC clutch bearing replacement experience.
A close-up of the electromagnet reveals a green felt seal. I believe this seal protects against dirt and debris from the clutch. The clutch drive protrusion fits within this area and is somewhat sealed by the felt.
Continuing the disassembly sequence, the electromagnet has also been removed, secured by another circlip. Notice the green dye on the clutch sprocket – a clear sign of a leak!
Looking into the front assembly of the compressor, where all the removed components were located, you can see green gunk – a mixture of lubrication oil and UV dye.
This confirms the Fiesta’s AC system leak originated from here. Compressor leaks typically occur in three areas: inlet/outlet pipes (usually easily fixed with O-ring replacement) or, most commonly, the front seal of the compressor shaft. This front seal leak is what we identified as the issue. Using a UV light, we traced the dye to the front of the compressor, confirming the source.
Observe the splines on the shaft, matching the splines on the clutch plate. This direct connection between the clutch and compressor shaft means that when the clutch engages, it locks the rotating pulley to the stationary compressor shaft, initiating compressor rotation.
Deeper inside the recess, you’ll notice another bearing and circlip. Theoretically, these components are replaceable. However, in practice, it’s a complex and tricky task requiring specialized tools. In many Western countries, replacing the entire compressor for a front seal leak is the standard practice. Individual parts can be difficult to source due to the variety of compressors used by car manufacturers. Furthermore, labor costs are high, and the risk of পুনরায় assembly issues or persistent leaks after seal replacement makes full replacement the more cost-effective and reliable solution.
Front seal failures are not typically common. Jack mentioned that Ford AC compressors rarely experience such problems. Perhaps we were just unlucky. Our 2015 Fiesta had approximately 97,000 kilometers on the clock.
The bearing/top of the seal is surrounded by a felt piece. While its exact function is uncertain, I suspect it provides extra protection against dirt and grime for the bearing and front seal. Insights from anyone with more knowledge on this would be appreciated.
After removing another circlip, we can begin separating the compressor body. It comprises three main sections. I’ve detached one section, while the middle section, containing the cylinders, remains connected to the rear, which houses the control solenoid and valve plates.
Continue exploring BHPian Jeroen’s thread on car AC compressors for further insights and detailed information.
