Why is My Central AC Running but Not Blowing Air?

Figure 1: Central AC is blowing air.

Air conditioners are used very frequently in summer, and the possibility of problems is very high. Air conditioner common faults are
·Blockage of the refrigeration system, the air filter, the air inlet and outlet, etc.;
·Motor windings, fan motor windings, solenoid valve coils, relay coils and contacts are burned;
·The fan and the bearing moving parts, etc are stuck.

So, what is the reason why the central air conditioner is running but not blowing air? What should be paid attention to when using the central air conditioner?

1. Reasons for AC Running but Not Blowing Air

When the central air conditioner is running, but there is no air coming out of vents, there may be something wrong with the air conditioner, or also may be minor problems caused by improper use.

Note that whether it is cooling or heating, the air conditioner needs a certain reaction time to work, so in a few minutes it may not blow air out.
During heating, it takes three to five minutes for the unit to blow air. This period is the process of warming up and preventing blowing cold air out.
During cooling, at the beginning, the air out is natural wind without temperature difference, so it’s needed to wait for some time.

After waiting for a long time, if there is still no air coming out, it may be caused by the following reasons：
●Clogged Filter
●Faulty Fan
●Damaged Circuit Board
●Aging AC

1.1 Clogged Filter

No air coming out may be due to clogged air outlet filters. When it is found that the air conditioner does not blow out air, first check the filter screen at the air outlet. After long-term use, it will definitely cause the accumulation of dust and other dirt. In this case, the air conditioning filter should be cleaned regularly to remove the dust in it.

Figure 2: HEPA filters for central air conditioners.

1.2 Faulty Fan

It may be the problem of the fan. Remove the cover of the window air conditioner indoor unit, find the fan under the air outlet, and try to rotate it by hand to see if it can rotate easily. If it doesn’t work, it means that something is stuck inside or the fan motor bearing is short of oil. If it can rotate, then the fan capacitor may be bad.

If there is no air blown out at the outlet of the air conditioner due to a fan failure, it is necessary to consider replacing or repairing the fan to make it work normally.

1.3 Damaged Circuit Board

If the air outlet of the air conditioner does not blow out air due to a damaged circuit board, please send it for repair. Regarding professional issues, it is best to seek professional maintenance personnel for help.

1.4 Aging AC

AC not blowing air may be due to the low speed running of the old air conditioner. When the air conditioner is aging, it will naturally need more time to start slowly. Of course, if it is too old, it can only be replaced.

In short, if there is no air out at all when the central air conditioner is working, it may be that the fan capacitor is broken, the fan seat is loose or stuck, the fan speed slows down, the air outlet or return air outlet of the air conditioner is dirty and blocked, the return air duct has poor ventilation, and the thermostat module of controlling air speed is broken.

2. What Should be Paid Attention to When Using Central AC?

Figure 3: Central air conditioning system diagram.

2.1 Don’t Switch on and off the AC Frequently

For the central air conditioner, the first thing to pay attention to during use is not to switch it on and off frequently. Because frequent switching on and off will not only increase power consumption of the AC unit, but also easily damage it. If you don't use it for a short time, you can set it to an energy-saving state.

2.2 Set Proper Temperature

When using a central air conditioner, both the air volume and the temperature must be set appropriately. During cooling, the normal operation is to select the strong wind mode when starting the AC, and after it has been running for a period of time and reached the set value, it can be switched to the low-level mode to run, which can play a very good role in saving energy.
In addition, for smaller rooms, when the temperature reaches the set value, a thermostat can be used to control it, which will also save electricity.

Also, if you use air conditioners for heating in winter, it is better to adjust the room temperature between 16°C and 26°C, and the best temperature is 20°C. Do not set the indoor temperature too high, which is not only beneficial to health, but also prevents the air conditioner from overloading. When heating, use the low wind gear first after turning on the AC unit, and then switch to the middle wind gear after half an hour.

Please do not set the temperature at the extreme 30°C that the air conditioner can withstand in winter, otherwise it will cause the air conditioner to start frequently or not stop, increase power consumption, and even damage the air conditioner compressor in severe cases.

Figure 4: Siemens central air conditioning thermostat.

3. FAQs

3.1 Why the Central AC Fan Turns but No Air Comes out of Vents?

There may be several reasons why the fan of the central air conditioner is running but there is no wind at the vent.

Dirty air filter: The air filter of the central air conditioner will adsorb dust and dirt in the air. If it is not cleaned and replaced for a long time, the filter will become dirty, causing the air not to circulate.

Insufficient refrigerant or clogged pipeline: Insufficient refrigerant or clogged pipeline of the central air conditioner will also affect the cooling effect of the air conditioner, resulting in the inability to blow cool air from the vent.

If the fan of the central air conditioner is working but there is no air out, first check the direction of the vent and the cleanliness of the air filter. If the problem cannot be solved, you need to find professional air conditioner maintenance personnel for inspection and maintenance.

Figure 5: Daikin central air conditioner maintenance.

3.2 Why is My AC Running but Not Cooling?

What's the matter with the cooling air conditioner not cooling but running normally?

Insufficient refrigerant
Generally, the old air conditioners that have been used for three to four years still work, but the cooling effect has declined. This is because old-fashioned air conditioners use Freon as a refrigerant, which will evaporate after long-term use.
Therefore, just re-add a little refrigerant to the system. In addition, it does not rule out the leakage of Freon caused by improper installation, and the problems of the machine itself.

Insufficient power supply voltage
The air conditioner compressor has a voltage range that allows it to work normally, and the compressor may not work properly or start when the voltage is lower than this range.

Insufficient air conditioner power
The general selection principle of air conditioners is: 150-250W/square meter for cooling and 250-350W/square meter for heating. In addition, factors such as space height, room orientation, and sealing performance need to be considered comprehensively.

Too high external environment temperature
There is a relatively common saying: when the air conditioner unit outside is in an environment above 43°C, most air conditioners have difficulty transferring indoor heat to the outside, resulting in no cooling.

No cleanness and maintenance of air conditioner for a long time
Because the outdoor unit is exposed to the outdoors, it is easy to adsorb dust and debris. If it is not cleaned for a long time, it will affect the heat dissipation performance of the air conditioner and reduce the cooling effect.
The indoor unit is related to the health of the human body. If it is not cleaned for a long time, bacteria will breed, pollute the air, and make people sick.

Too long copper pipe
The copper pipe connecting the indoor unit and the outdoor unit is too long. The maximum allowable length of the connecting pipeline of the air conditioner shall not exceed 8 meters for 1 hp, 10 meters for 1.5-2 hp, and 15 meters for more than 2 hp. The height difference between indoor and outdoor units shall not exceed 5 meters.

3.3 Why is My AC Not Blowing Cold Air?

Figure 6: Measuring central air conditioner wind speed.

There are generally 4 reasons for the air conditioner not blowing cold air: low voltage, lack of refrigerant, excessive dust, and AC compressor failure.

Low voltage
If the power supply voltage is too low, it is not a fault of the air conditioner. It is recommended to install a power regulator to make the voltage reach the range that the air conditioner can work normally.

Lack of refrigerant
Generally, long use time and improper installation will lead to the lack of refrigerant in the air conditioner, so that the air conditioner won’t blow cold air. It is recommended to add the refrigerant in time.

Excessive dust
Generally, there is too much dust on the filter screen of the indoor unit, which blocks the air circulation. Then it is recommended to clean the air conditioner once for 2-3 months.

AC Compressor failure
The final reason is the failure and aging of the AC compressor. For such problems, it is recommended to hire professionals to repair and maintain, so as not to cause secondary damage to the air conditioner.

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