How to Choose a Fuse for Automotive Air Conditioning Systems
Proper fuse selection is critical for protecting your vehicle's air conditioning system from electrical faults. This guide will help you understand how to choose the right fuse for your car's AC system, ensuring both safety and optimal performance.
Understanding Automotive Air Conditioning Systems
The refrigeration system of automobile air conditioning is a completely sealed circulation system. The failure of any one of the components will make the automobile air conditioning system unable to operate normally, and the failure of the refrigeration system cannot be removed at random.
As automobile air conditioner R&D technicians, it is very important to master the analysis and judgment methods of common faults. Although the specific repair techniques and repair methods are different in different air conditioning system maintenance operations, the causes and analysis methods of faults are similar.
There are two kinds of common faults of automobile air conditioning: heating system fault and refrigeration system fault. This paper mainly analyzes the non-refrigeration fault, insufficient refrigeration fault and noise fault of refrigeration system.
System Fault Diagnosis
Start the engine, turn on the air conditioner switch, turn on the blower switch, and set the temperature at a lower position. If there is no cold air blowing out from the air outlet, this situation should be analyzed from both electrical and mechanical aspects.
1. Electrical Fault
If the system does not refrigerate, it mainly means that the compressor does not work. The basic control circuit of the compressor electromagnetic clutch is mainly a series circuit composed of the A/C switch of the air conditioner, the high voltage switch, the low voltage switch and the temperature controller. As long as one component fails, the air conditioner compressor will stop working. The following inspection shall be carried out during troubleshooting.
(1) Check whether the main circuit of the compressor and the fuse of its control circuit are fused. If the fuse is fused, use a multimeter to check the resistance of the relevant circuit to the ground in sections, find out the abnormal grounding point in the circuit, and eliminate the fault.
(2) Unplug the harness connector of the compressor electromagnetic clutch, and directly connect the positive pole of the power supply to the circuit connector of the electromagnetic clutch coil. If the clutch works, the clutch is normal. Otherwise, replace or repair the electromagnetic clutch.
(3) Check the A/C switch (fan speed control switch), high voltage switch, low voltage switch, air conditioning relay contact and temperature controller in the circuit. When the power supply is connected by short circuit method, the switch to be checked is short-circuited respectively. If the air conditioning clutch works when a switch is short-circuited, the switch is faulty.
2. Mechanical Failure
(1) The compressor drive belt is broken and the compressor stops working.
(2) The refrigeration system is blocked, and the refrigerant cannot circulate, resulting in the system not refrigerating. Check the pressure in the system with the manifold pressure gauge. If the pressure on the low pressure side is very low and the pressure on the high pressure side is very high, the most likely parts of the system to be blocked are the receiver dryer and the expansion valve.
(3) The temperature sensing bulb of the expansion valve is broken and the internal liquid is lost, causing the pressure above the diaphragm of the expansion valve to be zero. Under the action of the spring force, the valve needle closes the valve hole, and the refrigerant cannot flow to the evaporator. Therefore, the system cannot refrigerate. After the thermal bulb is broken, the expansion valve shall be replaced with a new one.
(4) All refrigerant in the system leaks. Use a manifold pressure gauge to measure the system pressure. If the pressure at the high and low pressure sides is very low, it indicates that the refrigerant has leaked. The leak detector shall be used for detailed inspection to determine the leakage part and repair it. After repair, the system shall be vacuumized, and then sufficient refrigerant and refrigeration lubricating oil shall be added as required.
(5) The inlet and outlet valves of the compressor are damaged, and the refrigerant cannot be circulated. Use the manifold pressure gauge to detect the pressure in the system. If the pressure at the high and low pressure sides is close to the same, it indicates that the valve plate is damaged. After the valve plate is damaged, the compressor shall be disassembled for repair or replaced with a new one.
How to Choose the Right Fuse for Your AC System
Selecting the proper fuse for your automotive air conditioning system is crucial for preventing electrical damage and ensuring system longevity. Here's what you need to consider:
Fuse Selection Criteria
- Current Rating: Choose a fuse with a current rating slightly higher than the normal operating current of your AC system. Typically, automotive AC systems require fuses between 10-30 amps depending on the vehicle size and system capacity.
- Voltage Rating: Ensure the fuse voltage rating matches your vehicle's electrical system (usually 12V for cars, 24V for larger vehicles).
- Response Time: Consider fast-acting fuses for sensitive electronic components and slow-blow fuses for components with high startup currents like compressors.
- Physical Size: Select the appropriate physical size (mini, standard, maxi) that fits your vehicle's fuse box.
Important Safety Note
Never replace a blown fuse with one of a higher amperage rating. This can lead to electrical fires or permanent damage to your AC system components. Always identify and address the root cause of the fuse blowing before replacement.
Fault Diagnosis of Insufficient Cooling
1. Causes of Refrigerant and Refrigerant Lubricating Oil
(1) Insufficient refrigerant in the system. If the refrigerant is insufficient, the refrigerant injected into the evaporator from the expansion valve will be reduced, so that the heat absorbed by the evaporator during evaporation will be reduced, so the refrigeration capacity of the system will be reduced. When insufficient refrigerant is diagnosed, occasional bubbles can be seen in the sight glass, indicating that the refrigerant is slightly less. If there are obvious billowing bubbles, it indicates that the refrigerant is much less.
(2) Excessive refrigerant injection. There are many refrigerants, which occupy a large capacity and affect the heat dissipation effect. Because the refrigeration effect and heat dissipation effect are two thermodynamic processes of heat absorption and heat release, poor heat dissipation will directly affect the refrigeration effect. If no bubbles can be seen in the sight glass, the pressure on both sides of the high and low pressure of the refrigeration system will increase, and the excess refrigerant can be discharged by the manifold pressure gauge.
(3) Refrigerant and lubricating oil contain dirt. Due to the large amount of dirt, the filter screen of the filter is blocked, which reduces the refrigerant flow and affects the refrigeration effect. Touch both ends of the dryer by hand. Normally, there is no temperature difference. If the temperature difference is obvious, it indicates that the dryer is blocked. The manifold pressure gauge can be used for detection. If the pressure on the high pressure side is too high and the pressure on the low pressure side is too low, it indicates that the high pressure side is blocked. Otherwise, the dryer is blocked and needs to be replaced.
(4) Refrigerant contains air. Air is a substance with poor heat conduction. Under the system pressure and temperature, it cannot be dissolved in the refrigerant. The refrigerant mixed with air affects the heat dissipation of the system. Some air circulates in the system with the refrigerant, which reduces the amount of refrigerant ejected from the expansion valve and reduces the refrigeration capacity. When the refrigerant passes through the orifice of the expansion valve, the moisture in the air causes "ice resistance" at the orifice of the expansion valve due to the rapid drop of its pressure and temperature. Stop the machine for a while, and the system will resume operation after the ice melts. In this case, it is necessary to vacuumize and refill the refrigerant.
2. Mechanical Reasons
(1) The working performance of the compressor is reduced.
The fault and diagnosis and repair methods of compressor performance degradation are as follows.
- If the pressure on the high pressure side is low and the pressure on the low pressure side is high, it can be diagnosed as compressor leakage. The reason is that the compressor has been used for a long time, due to the wear of the cylinder and piston, the cylinder clearance increases and the intake and exhaust valves are not closed tightly, which will cause air leakage, so that the actual displacement of the compressor is far less than theoretical displacement. Solution: Replace the compressor.
- The driving belt of the compressor is loose and slips during operation, resulting in low transmission efficiency. If there is an air conditioning control system with a synchronous sensor, it can automatically monitor whether the ratio of compressor speed and engine speed is constant, and if it exceeds a certain difference, it will automatically cut off the compressor electromagnetic clutch circuit. Solution: Tighten the drive belt.
- The joint surface between the electromagnetic clutch pressure plate and the belt pulley is seriously worn or contaminated with oil, resulting in slippage during operation. If the resistance of the electromagnetic clutch circuit is too large or the power supply voltage is too low, the electromagnetic clutch coil will not attract enough force to cause the clutch to slip. Solution: First, observe whether the clearance between the clutch pressure plate and the pulley is uniform and whether the pressure plate is twisted. If it cannot be repaired, replace the clutch.
(2) The heat dissipation performance of the condenser is reduced.
There is sludge on the surface of the condenser, which is covered or blocked by sundries, and the fins are deformed. In addition, the cooling fan drive belt is loose or the rotational speed is too low. Solution: Adjust the tension of the driving belt, remove the dirt and covering on the surface of the condenser, and trim the bent fins.
(3) The amount of cold air blown out from the air outlet is insufficient.
Frost on the surface of the evaporator or the speed of the blower drops, which will make the amount of cold air blown out insufficient. Solution: Check the blower speed control switch, blower motor, blower relay and other circuits.
Fault Diagnosis of Noise in Refrigeration System
(1) The knocking sound of the high pressure pipe and compressor caused by excessive refrigerant. At this time, the refrigerant should be discharged until the display value on the high pressure side is normal.
(2) Insufficient refrigerant causes "hissing" sound at the inlet of the evaporator. At this time, check whether there is leakage. If there is leakage, make up the leakage and then add enough refrigerant.
(3) If there is excessive moisture in the refrigeration system, the dryer shall be replaced, the original refrigerant shall be discharged, and the system shall be vacuumized again and filled with refrigerant.
(4) The abnormal noise of the compressor clutch mainly comes from the compressor and the electromagnetic clutch. The main reasons for the abnormal noise are as follows:
① Screaming. The squealing sound is mainly caused by the clutch slipping when it is engaged, or by the belt being too loose or worn.
② Vibration. Compressor vibration and shaft vibration are also one of the sources of abnormal noise. First, check whether the support is broken, whether the fastening bolts are loose, and whether the belt tension is too tight or the pulley axis is not parallel to cause the compressor vibration. Excessive bearing wear of the compressor can also cause shaft vibration. Poor lubrication of the pulley bearing can also cause abnormal noise.
Diagnosis and Elimination of Abnormal Sound or Vibration in Air Conditioning System
1. Fault Phenomenon
Abnormal sound or vibration during operation of the air conditioning system.
2. Cause of Failure
(1) The driving belt of the compressor is loose and excessively worn, the belt pulley is deflected, and the bearing of the belt tensioning wheel is damaged.
(2) The compressor mounting bracket is loose or the compressor is damaged.
(3) Too little refrigeration oil causes dry friction or close to dry friction in the mating pair.
(4) The electromagnetic clutch slips due to improper clearance, excessive wear, oil stain on the mating surface, low battery voltage, etc.
(5) The electromagnetic clutch bearing is damaged and the coil is installed improperly.
(6) The blower motor is excessively worn or damaged.
(7) There is too much refrigerant in the system, resulting in noise during operation.
Professional Tip
When diagnosing AC system issues, always start with the simplest and most accessible components before moving to more complex ones. Check fuses, relays, and electrical connections first before considering compressor or condenser replacement, which are more costly and time-consuming repairs.
Preventive Maintenance for Automotive AC Systems
Regular maintenance is key to preventing AC system failures and ensuring optimal performance. Here are essential maintenance tips:
- Regular Inspection: Check your AC system at least twice a year, ideally before summer and winter seasons.
- Clean Condenser: Keep the condenser fins clean from debris, bugs, and dirt that can reduce cooling efficiency.
- Check Drive Belts: Inspect compressor drive belts for wear, cracks, or improper tension.
- Run AC Regularly: Even in winter, run your AC for 10-15 minutes weekly to keep seals lubricated and the system functional.
- Cabin Air Filter: Replace cabin air filters according to manufacturer recommendations to maintain airflow.
- Professional Service: Have a professional AC service every 2-3 years to check refrigerant levels and system integrity.
Frequently Asked Questions
The correct fuse size depends on your specific vehicle make and model. Typically, automotive AC systems use fuses between 10-30 amps. Consult your vehicle's owner manual or the fuse box diagram for the exact amperage rating. Never install a fuse with a higher amperage than specified, as this can lead to electrical damage or fire hazards.
AC fuses don't require regular replacement unless they blow. A blown fuse typically indicates an underlying issue in the electrical system. If your AC fuse blows repeatedly, have your system professionally diagnosed to identify and address the root cause rather than continuously replacing fuses.
Common reasons for repeatedly blown AC fuses include: short circuits in the wiring, a failing compressor clutch drawing excessive current, a faulty blower motor, or issues with other AC components creating electrical overloads. Professional diagnosis is recommended to identify the specific cause.
No, you should use the specific type of fuse recommended by your vehicle manufacturer. Automotive fuses come in different types (blade, cartridge, ceramic) and sizes (mini, standard, maxi). Using the wrong type can lead to poor electrical connections or even damage to the fuse box.
Electrical issues often manifest as complete system failure (no operation at all), blown fuses, or intermittent operation. Mechanical problems may show as reduced cooling performance, unusual noises, or leaks. If your AC isn't working at all, start by checking fuses and relays before investigating mechanical components.
Fault diagnosis of automotive air conditioning is a process that requires systematic thinking and careful operation. Whether it's an electrical problem or a mechanical failure, we need to investigate step by step, from the phenomenon to the essence, to find the root of the problem. It is hoped that the analysis of this paper can help us better understand and deal with the common faults of air conditioning system.
Remember that regular inspection and maintenance is more economical and worry-free than repair after a fault occurs. Especially before the arrival of high temperature in summer, it takes a little time to test the air conditioning system, which can avoid many inconveniences in driving.
If you encounter an uncertain situation in the operation, you might as well consult the manual or consult a professional technician first—safety and accuracy are always the first priority.
