AC Compressor
What is an AC compressor?
An AC compressor is a pump which creates the heat by putting the air conditioning refrigerant under extremely high pressure. The AC compressor is called a pump because both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible; while some can be compressed, the main action of a pump is to pressurize and transport.
How does an auto AC compressor work ?
The compressor is the heart of the air-conditioning system because it circulates or pumps refrigerant and oil through the system.
The compressor is responsible for two main functions required by air-conditioning system.
- One function of the compressor is to raise the pressure of the refrigerant.
- It is critical that the refrigerant be hotter than the temperature of the ambient (surrounding) air; otherwise, no heat transfer would take place.
- The second function of the compressor is to create low pressure in the evaporator. The lower pressure condition in the evaporator allows the refrigerant to vaporize (boil), enabling the refrigerant to absorb large quantities of heat energy from the cab of the vehicle.
- The compressor also circulates the refrigerant and compressor oil, which are mixed together throughout the air-conditioning system.
Failure of either of the compressor’s two main functions would result in a loss or reduction of refrigerant circulation within the air-conditioning system.
Without proper refrigerant circulation, the cooling process of the air-conditioning system will be reduced or will stop working altogether.
Air conditioning compressors come in may different styles, but all perform the same function. In most cases, the compressors are mounted near the front of the engine. The compressor is belt-driven from the engine crankshaft. The compressor’s drive pulley is incorporated into an electromagnetic clutch. This clutch provides a means of turning the compressor on or off, depending upon the temperature requirements of the system.
Two refrigerant lines are attached to the compressor, one being the discharge line and the other the suction line. The refrigerant lines can always be identified by their physical size. The suction line is always larger in diameter than the discharge line.
The suction (inlet) side draws in low-pressure, low-temperature refrigerant gas from the evaporator. The compressor then pumps out high-pressure, high-temperature refrigerant gas to the condenser.
Two-piston-type compressor operation.
Intake Stroke: Whenever the piston is moving in a downward direction, it can be considered to be on an intake stroke. As the piston moves down in the cylinder, the volume becomes greater and the pressure is reduced. The refrigerant gas is then drawn into the cylinder from the suction (low pressure) side. To accomplish this, the refrigerant must first enter the intake port and push the intake reed valve down (open) so that it may be drawn into the cylinder.
Compression Stroke. When the piston then starts its upward travel, the volume within the cylinder is reduced, causing a rise in pressure. The instant the pressure within the cylinder exceeds that of the suction line, the intake reed valve closes. The closing of the inlet valve allows the piston to continue to raise the pressure within the cylinder. The discharge reed valves are held closed by springs so that they act like a check valve. Once the pressure within the cylinder exceeds the force of the closing springs and the refrigerant pressure in the discharge line, the valve opens, allowing the high pressure refrigerant gas to be pushed out into the discharge port and eventually into the discharge line.
Swash Plate Compressor Operation.
Intake Stroke. As the swash plate pulls the piston down in the cylinder, it creates a drop in pressure. This pressure is lower than that of the refrigerant in the suction line. This imbalance in pressure forces the higher pressure of the refrigerant within the suction line to open the suction reed valve, allowing the cylinder to be filled with refrigerant gas.
Compression Stroke. Further rotation of the swash plate changes the direction of the piston within the cylinder. As the refrigerant is compressed slightly, it creates a pressure higher than that contained within the suction line. This pressure imbalance causes the suction reed valve to close, preventing refrigerant from exiting the cylinder through the suction port. The pressure within the cylinder rises to a point where the discharge reed valve opens, allowing the superheated refrigerant to be pushed out of the cylinder into the discharge port and on out the other components of the air-conditioning system.
Rotary Vane Compressor.
The compressor drive pulley is belt-driven from the engine crankshaft pulley. Turning the rotor assembly causes the vanes to extend by centrifugal force, and causes them to seal against the cylinder wall. As the vane passes the suction inlet, the volume of the chamber increases, causing a lower pressure that draws refrigerant into the cylinder. Once the vane passes the largest portion of the eccentric, the vane will be pushed back into its bore as if follows the eccentric shape. This causes the volume of the chamber to decrease, squeezing the refrigerant between the vane and the cylinder wall, and increasing the pressure and temperature of the refrigerant. The high-pressure, high-temperature refrigerant is then pushed out the discharge port and through the discharge valve out into the discharge line.
Variable displacement compressor operation.
The pistons of the compressor are driven by a variable angle swash plate. The angle of the swash plate is changed by a bellows-activated control valve located in the rear head of the compressor. The control valve senses the suction pressure and controls the swash plate angle based on crankcase suction pressure differential. Operation of the control valve is dependent on differential pressure.
Scotch Yoke Compressor operation.
The operation of this compressor is similar to that of all the other piston compressors. During the intake stroke, the piston moves down in its bore and refrigerant vapor is drawn into the cylinder through the suction reed valve. The piston changes its direction of travel on the exhaust stroke and compresses the refrigerant vapor to a high-pressure gas, pushing it through the discharge valve plate on the exhaust stroke.
Scroll Compressor Operation.
The scroll compressor operates by rotating one scroll within a stationary scroll. The ends of the rotating scroll coop up the refrigerant vapor at the suction port of the compressor. As the scroll continues to rotate, the inlet passage is sealed off and the volume of the passage becomes smaller, increasing the pressure of the refrigerant vapor. The refrigerant vapor is squeezed through to the discharge passage at the center of the scrolls. The refrigerant vapor is at a higher pressure and temperature as it leaves the discharge port.
Symptoms Of Bad AC Compressor
How to know if AC compressor is bad is actually not as difficult as you thought since the symptoms of bad AC compressor are clear to see. There are…. bad ac compressor symptoms which you may see when your car has a bad AC compressor. Following these symptoms will give you a basic knowledge to diagnose your car.
1. Higher Temperatures Than Normal In The Cabin
One of the first signs which is really to recognize symptoms of bad AC compressor is the AC no longer blowing as cold as it did. A damaged or failing compressor will not be able to properly regulate the refrigerant flow in the AC system, and as a result, the AC will not function properly. So you may notice that the degree inside the car increases and the airflow from the AC is hot. There are 3 possible reasons behind, first is the low level of the refrigerant, second is the leak of the refrigerant and the third is the compressor is going bad and needs to be replaced.
2. Loud Noise When Compressor Is Running
When the heating, ventilation, and air conditioning (HVAC) system operates, it tends to have some noise when it’s kicking on and off. But the loud noise when the AC switches on is another potential symptoms of bad AC compressor. The AC compressor has several interior components and uses a sealed bearing to turn. If any of the interior components break, or the compressor’s internal bearings fail or seize, then all sorts of noises can be produced as a result. The most valuable solution is changing the whole AC compressor.
3. Moisture Leaks
Most people who wonder what does a bad ac compressor sound like don’t know about the moisture leaks in the AC compressor. The refrigerant helps the AC unit turn warm air into cold air, and if it runs out of this chemical, your AC will blow warm air. When the refrigerant leaks out, it not only increases the potential harmful health concerns but also increases your energy consumption.
4. Compressor Clutch Is Not Moving
The clutch on the compressor is what allows the pulley to engage and disengage from engine power so that the compressor is only turning when it needs to be. The clutch keeps the compressor activated, if it breaks, the compressor will not be able to receive the engine power anymore. At the mechanic, the repairman will check the serious level of the compressor clutch, then they may decide to replace the clutch only or the whole compressor. Since it is possible to replace the clutch, it will reduce the cost for replacement.
5. Circuit Breaker Tripping
If your outside condensing unit keeps losing power and tripping the circuit, it is one of the symptoms of bad ac compressor. The reason behind is the overheating and drawing too much power, causing the circuit breaker to trip. The tip is do not just keep resetting the circuit breaker and turning the system back on. The circuit breaker is doing the job to protect you from the potential fire hazard.
6. Broken Suction Lines
The refrigerant line in the AC system can be blocked if the compressor is failed to operate, leading to the result of hot airflow in the car. You can fix this problem by taking your car to the mechanic. The repairman knows how to remedy this issue by unblocking the refrigerant lines, but if he’s not successful, the lines will need to be replaced.
7. Damaged Wire
When you do the maintenance at home, you may notice the damaged wiring of any sort. It is a bad ac compressor symptom. Damaged wiring presents a huge safety concern because it can easily lead to an electrical fire. When an AC unit is exposed to electrical problems, it can lead to the compressor receiving too much or too little voltage. This quickly damages the compressor and results in the replacement of a new AC compressor.
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