Car Vibrates When Idle And AC Is On (How To Fix)

‍Car Vibrates With AC On

There are a number of reasons this issue can be happening. Let’s take a look at the list below to narrow down where your issue could be coming from.

Check worn out engine mountings

The engine mounts are responsible for securing the engine to the car's chassis. Over time, these mounts can wear out or become damaged, which can cause the engine to vibrate excessively. You can inspect the engine mounts for visible signs of damage or wear, such as cracks or tears. If you suspect that the engine mounts are the cause of the vibrations, they will need to be replaced.

Clean the idle air control valve (IAC)

The IAC is responsible for regulating the engine's idle speed. If it becomes dirty or clogged, it may not function properly, which can cause the engine to vibrate. You can clean the air control motor valve by removing it and using a carburetor cleaner to remove any dirt or debris. If cleaning the IAC valve does not solve the problem, it may need to be replaced.

Inspect the AC compressor

The car's air conditioning system is responsible for circulating the refrigerant through the AC system. If it is damaged or not functioning properly, it can cause the engine to vibrate. You can inspect the AC compressor for visible signs of damage, such as leaks or cracks. If you suspect that the AC compressor is the cause of the vibrations, it will need to be repaired or replaced.

Check the spark plugs

Worn spark plugs can cause the engine to run rough and vibrate. You can inspect the spark plugs for wear or fouling, and replace them if necessary.

Faulty Fuel Injector

Also, check for a defective fuel injector. Dirty fuel injectors can sometimes lead to a rough idling issue and cause a car shake.

Dirty Throttle Body

Sometimes, a dirty throttle body can cause a vehicle engine to idle rough. As well a bad throttle position sensor can cause the same issue. The throttle manages the air intake of a car, so if it’s dirty, it might not be allowing the correct amount of airflow into the engine and causing the car’s engine to vibrate.

Check the AC system for leaks

A leak in the air conditioner system can cause the AC compressor to work harder than it should, which can cause the engine to vibrate. You can inspect the AC system for leaks by using a UV dye and a black light. If you find a leak, it will need to be repaired.

The issues outlined above are a good starting point to check for the issue. But if your car shakes only while the air conditioning compressor is running, and stops shaking when you turn it off, it's most likely a faulty ac compressor. That would be the best place to start.

How Does An AC Compressor Work

An AC compressor works by being driven by a belt that's run by the crankshaft. The belt spins a compressor that draws in refrigerant from the AC system’s low side and compresses it into a high pressure gas.

The high pressure gas is then sent to a vehicle’s condenser, which is located in front of the vehicle’s radiator. The condenser removes heat from the compressed refrigerant gas and condenses it into a high pressure liquid.

The high-pressure liquid then flows through the expansion valve, which reduces the pressure and temperature of the refrigerant. The low-pressure, low-temperature refrigerant then enters the evaporator, which is located inside the vehicle's cabin.

The evaporator removes heat from the air inside the cabin, causing the refrigerant to evaporate into a gas. The low-pressure refrigerant gas is then drawn back into the compressor, completing the cycle.

This cycle repeats continuously to provide cool air to the cabin. The compressor is equipped with a clutch that engages and disengages the compressor pulley from the engine's crankshaft, allowing the compressor to turn on and off as needed. This helps to conserve energy and prolong the life of the compressor.

Inspecting a A/C System

Inspecting an AC compressor is an important part of maintaining a vehicle's AC system. Here are the steps you can follow to inspect an AC compressor:

• Check the compressor belt: Inspect the compressor belt for any signs of damage or wear. Make sure the belt is tight and properly aligned. If the belt is loose, damaged or misaligned, it can cause the compressor to malfunction.
• Look for leaks: Inspect the compressor and surrounding components for any signs of leaks. You can use a UV dye and a black light to help identify any leaks in the system. If there are leaks, it is important to repair them before inspecting the compressor further.
• Check the compressor clutch: Look under the hood and check the compressor clutch. It should engage and begin to spin when the AC system is turned on. If the clutch does not engage, it may be faulty.
• Measure system pressure: Use an AC manifold gauge set to measure the high and low side pressure of the AC system. The pressure readings will depend on the type of AC system and the ambient temperature. Compare the readings to the manufacturer's specifications. If the pressure is outside of the recommended range, it may indicate a fault with the compressor.
• Test the compressor clutch coil: Use a multimeter to test the compressor clutch coil. Set the multimeter to the resistance setting and measure the resistance of the clutch coil. Compare the reading to the manufacturer's specifications. If the resistance is outside of the recommended range, it may indicate a fault with the compressor.
• Check for abnormal noises: Turn on the AC system and listen for any abnormal noises coming from the compressor. A faulty compressor may make a loud, squealing, or grinding noise.
• Inspect the compressor for physical damage: Inspect the compressor for any physical damage such as cracks, dents, or signs of corrosion. If there is any damage, the compressor may need to be replaced.

If any of these inspections indicate a fault with the compressor, it will need to be repaired or replaced. It is recommended to have a qualified mechanic perform these inspections and make any necessary repairs to ensure that the AC system is functioning properly and safely.