Why Does My Car Air Conditioner Only Work On High?

While driving, you may have noticed that your car air conditioner only works on high, but don't know why this happens. Fortunately, we have done some research for you, and here's what we gathered.

If your car air conditioner starts working on high, this means your blower motor, the control board, or the thermostat may be having issues. However, a complete diagnostic check-up is needed to make sure the problem isn't from switches, wiring, and fuses.  

Sometimes, the resistor can be difficult to reach, so it is better to contact a good technician for a proper diagnosis. Continue reading to find out how to deal with car air conditioners that only work on high.

rear ventilation duct and climate-control pane, Why Does My Car Air Conditioner Only Work On High?

Why Car Air Conditioners Only Work On High

The blower motor works together with a resistor. The resistor can control the output speed of the blower motor with voltage. The blower motor resistor can easily overheat and corrode. So, when the resistor is having issues, the highest setting becomes the only option.

This happens because the blower motor's air bypasses the resistor, gaining the highest amount of voltage. The process brings about full power. Sometimes the problem could be that your AC module or switch to your fan is faulty. Checking air flow of an ac

What Is Blower Resistor?

A blower resistor is a device that regulates the temperature of an air conditioner. It is usually mounted on the outside of a car.  It helps to regulate the amount of power that goes into the compressor.

Blower resistors are designed with a fan and a resistor, which creates a voltage difference between the two terminals of the device, causing it to generate an electric current. This current then runs through the fan and creates a wind blowing inside the system.

A blower resistor helps cool the cabin of a vehicle,  it also helps to prevent corrosion on the compressor. This device is usually made from aluminum, copper, or nickel-plated steel.

How Do You Fix An Air Conditioner That Only Works On High?

air conditioning and controls of modern car

To solve this problem, you should try fixing your resistor. Also, if you have attempted to turn the temperature of your AC down and have noticed that it doesn't work, then you might have a problem with the thermostat. Try checking your thermostat to make sure it is set at the appropriate temperature.

Also check if your AC has a problem with the compressor or the condenser, if it does, try dealing with the problem. Another thing to do is to turn off the AC for a while before turning it back on again. If none of these work, then your best bet is to contact an HVAC technician to help you with the problem.

How Do You Know If Your Blower Motor Is Bad?

Ac panel of a car

As a car owner, you may want to know when your blower motor needs replacement. Here are some signs that your blower motor is bad and needs to be worked on:

Weak Airflow

If you notice a weak flow of air, there are chances your blower motor is faulty. Most people notice this sign immediately after their blower motor starts going bad.

Your motor tends to wear out as time goes on, which is just among the general wear and tear car experiences. When this starts happening, the motor may not be capable of pushing as much air through the HVAC system of your vehicle. This makes the blowers wear out. 

Unusual Noises

Sometimes foreign objects get sucked into the blower motor fan. Since the fan's blades are mostly plastic, they can easily get damaged or even break off. You may notice a noise such as slapping or unusual pop from the back of the vent when this happens. The noise may change with speed or direction of travel, becoming louder when you try to accelerate.

You need to listen for this noise especially during the summer months when the AC is in use and if it's present, contact a technician for help.

Smoke Or Unpleasant Smells

At times, you may start noticing strange smells and seeing smoke while driving. If this happens, it is advisable to stop your vehicle immediately. A burned-out blower motor will not damage your car, but you might not be certain that the smoking is from the blower motor. Make sure to check your vehicle before continuing your journey.

Why Does My AC Only Work On Fan?

If you notice that your AC compressor has stopped working but the fan is running, the problem could be that power is not reaching the outer unit hosting the compressor. The reason the fan continues running is that the central unit is not having such a problem.
If your compressor has refused to start, try taking a look at the wiring that connects both units. You should also check for faulty compressor clutch. This can be done by using a multimeter to measure the voltage at the compressor clutch. 
turning on car air conditioning system

Why Does My AC Not Work At High Speeds?

There are many reasons why your car’s air conditioner might not work at high speed. The most common reason is that the compressor is not working properly. You can fix this problem by cleaning out the AC system and checking for any leaks. If you notice that your compressor has been damaged, then you should change it as soon as possible.

If your condenser fan needs replacement, your AC may not work at high speed. You can also experience a similar problem if your condenser fan belt comes loose and needs to be replaced.

Why Does My Fan Speed Only Work On High?

When your blower resistor starts having problems, the only functioning part of your AC is usually the highest fan speed. This is because it bypasses the resistor, gaining the highest amount of voltage. A working resistor drops the amount of voltage channeled to the lower fan speeds, making the fan run slower.

If your fan speed only works on high, it could also be because of an obstruction in front of the radiator grille. If there is something blocking the grill, then it will not allow cool air to enter, and you will need to look into getting rid of that obstruction before your AC will work properly again.

Why Is My AC Not Blowing Strong In My Car?

air deflector in the car

When the AC in your car stops blowing as strong as it should, it could be a sign that there is something wrong. Here are some causes of the problem:

Growth Of Mold And Mildew

When moisture accumulates inside air conditioner units, it creates a suitable environment for mold and mildew to flourish. This affects airflow by clogging the fins at your heat exchangers that are at the back of the dashboard. This may bring bad odors into the cabin, which may endanger the health of your passengers.

Loose Seal

This is another cause of weak airflow. When your blower hose is loose, enough air will stop passing through the evaporator into the cabin. There might also be something wrong with one of the seals in the system. The seals are supposed to be tightly closed so air can pass through. It is the work of a professional technician to repair or change hoses and seals. 

Clogged Cabin Filters

The cabin filter, also known as a pollen filter can be found before your blower motor. It is a filtration system between the external air and your vehicle's cabin. Dirt, pollen, leaves, or other debris is usually stopped at the cabin filter so your passengers can receive clean air. You have to clean them often so they won't get blocked.

Can I Upgrade My Blower Motor?

As a car owner, you may want to increase the airflow of your AC if your blower motor is still at a low speed. This can be done by changing your blower motor's speed. The black wire on most blower motors is for high speed.

To Wrap Up

rear ventilation duct and climate-control pane

A series of resistors are usually used to make the heater blower motor work at speeds that vary. So, when there are burnouts, just one heater blower motor speed, high, is left. The high setting is the most efficient way for your car air conditioner to cool down your vehicle's interior. The resistor module can be easily replaced and is also inexpensive.

If you enjoyed reading this post, here are related articles you might find interesting:

Car Air Conditioner Turns On And Off - What Could Be Wrong?

Carrier Air Conditioner Not Cooling - What's Wrong?

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