Usually, when AC is switched ON, you are possibly expected to blow hot air for a while until the evaporator becomes cool enough to blow cold air. That is normal. When you take your car along the route and suddenly realized that your AC started to blow hot air, then you for sure there is an underline reason for the car’s AC malfunction.
Here is a simple guide that will help you find out the underline reason. In this powerful guide, you are going to quickly learn the eleven reasons for a car air conditioner which start blowing warm air.
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Car AC Blows Cold Then Warm
An automotive air conditioning that blows cold air for a while than warm air is called Intermittent cooling. A car air conditioner starts cold and then gets warm feels like the AC is tricking you. There are several reasons why a car’s ac system blows cold than warm. Here, you will find the possible causes for a car AC blowing cold and warm air.
11 Reasons For Car Air Conditioners to Blows Cold Then Warm
Below are the eleven complete reasons for a car air conditioner to blow cool air and then warm.
- Moisture In The AC System
- Blocked Drain Pipe
- Blocked Expansion Valve/Orifice Tube
- Defective Compressor Clutch
- Refrigerant Overcharged
- Discharged Battery
- Blown Fuse
- A Corroded Relay
- Faulty AC Control Switch
- Slow Blower Fan Speed
- Bad Sensors
1. Moisture In The AC System
You might get surprised to know that the most common reason the car air conditioner runs cold than warm is MOISTURE. Usually, air conditioning starts cool and then goes warm, in most cases due to moisture freezing up in the evaporator.
Whenever evacuating or recharging the AC system, if care is not taken, contaminated air can enter the system. A mixture of moisture and refrigerant is created and starts to freeze up near the expansion valve in the evaporator and the refrigerant circulation is stopped. Thus, warm air starts to blow due to restrictions in the refrigerant path caused by a mixture of impurities. The refrigerant flow resumes when the ice melts in the evaporator.
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The main reason, the moisture needs to be removed from the AC system is to prevent it from freezing up, which blocks the refrigerant flow. Because water has a freezing point of 32 degrees Fahrenheit, but the refrigerant freezing point is -142 degrees Fahrenheit.
2. Blocked Drain Pipe
A hose of the drain pipe leaks out the condensed water from the car to the outside. A blocked evaporator drain pipe lets the evaporator dip into the condensed water, making it freeze up from the outside surface.
When the evaporator is blocked with ice, it will prevent gaseous refrigerant to get bypassed until ice melts and cold air returns, which results in, the car AC stops blowing cold air after a while.
3. Blocked Expansion Valve/Orifice Tube
The cold air process starts with the expansion valve. It decreases pressure from liquid refrigerant and allows expansion from a liquid of high pressure to low pressure. The phase of refrigerant changes here due to expansion from a liquid to a gaseous state and it is present in a vapor state in the evaporator.
Contaminated refrigerants such as metal particles, debris, and sometimes ice build into the valve, which results in a failing expansion valve causing a restriction of refrigerant flow. As a result, the car ac blows cold and then warm.
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4. Defective Compressor Clutch
An AC compressor clutch provides engine power for the compressor to start. It allows the pulley to engage and disengage the engine power from the compressor. With continuous usage, the compressor clutch is subjected to wear and tear, which forces to increase the clutch gap. So, overall it is hard for the clutch to maintain correct pressure and compel the compressor to set on the ON and OFF cycle. Thus, the AC compressor works intermittently.
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5. Refrigerant Overcharged
When the car AC system is overfilled with refrigerant, the high pressured refrigerant shuts off the car AC high-pressure switch, making the compressor deactivate.
So, when the AC is turned ON, it blows cold air at first, but soon the cold air turns to warm air because the high-pressure switch shuts off the compressor clutch, as a result, ac runs at different speeds.
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6. Discharged Battery
The battery provides voltage to the compressor coil to attract the compressor clutch making it activated. Sometimes, a very low battery voltage or faulty generator cannot produce enough amount of voltage for the air conditioner to run at full speed.
And sometimes, a high compressor’s coil resistance will not let the clutch engage, resulting in, the car air conditioner starting cold and then getting warm.
7. Blown Fuse
The fuse is the gatekeeper of your car’s electrical circuits. It kills itself when an unexpectedly high current flows in the circuit. Sometimes, a fuse is fired and the AC shuts off, leading the car air conditioner to blow cold and then warm.
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8. A Corroded Relay
A relay is an electromechanical switch used to control a high amount of current by utilizing a low amount of current. The relay has a coil, which when activated attracts the contact, making the connection of high amperage circuit. This coil gets old and its internal resistance increases.
So, a corroded relay will cut the current if its internal resistance increases due to heat, which leads the car air conditioner to blow cold and then warm.
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9. Faulty AC Control Switch
A faulty AC control switch can be the reason for car ac blowing hot air. The car AC control switch turns ON and OFF the air conditioner. A bad AC control switch that will not make good contacts can also be the reason for the car air conditioner blowing cold then warm then cold again.
10. Slow Blower Fan Speed
You can face this issue if the fan isn’t working. Because enough amount of cooling is not removed from the evaporator. As the evaporator temperature drops too much, the AC temperature sensor sends signals to the AC control Module to stop the AC. Which can force the AC to stop blowing cold air after a while.
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You must make sure at least one time that the blower fan runs for the first ventilation to remove enough cooling from the evaporator to protect it from freezing. Fans are important to exchange heat therefore most vehicles have two radiator fans.
11. Bad Sensors
The car’s electrical sensors provide important information to the AC control module to turn ON and OFF the car air conditioner. Sometimes, a bad temperature sensor, a bad control module, or a sun load sensor can also lead to car AC intermittent cooling.
How To Fix When The Car Air Conditioner Blows Cold Then Warm
There are a number of possible reasons for the AC blowing cold then warm, and different fixes in terms of severity. Here are some things you can do to diagnose and troubleshoot the issue:
- Check the refrigerant levels in the AC system. If they are low, you may need to consult a professional auto repair to recharge the system using an AC recovery unit.
- Inspect the compressor, condenser, and expansion valve for any visible damage or clogs. Also, check the valve, if any of these components are faulty or cracked then air and moisture can enter the system, you may need to have a professional repair or replace them.
- Make sure the radiator fan is working properly because it helps to remove heat from the gaseous refrigerant. If it’s not functioning correctly, it can cause the AC to blow warm air.
- Check for any AC leaks and make sure you choose AC leak sealer to seal them. Also, solve issues of other leaks like leaks of battery water under your car because some corrosive acids that eat away metal can harm the ac system.
- If you’re unsure of the cause of the issue or don’t feel comfortable attempting a repair yourself, it’s best to have a professional diagnose and fix the problem. Depending on the severity of the issue, the repair may involve recharging the AC system, replacing components, or sealing leaks.
In order to choose the best course of action, it’s important to consider the specific symptoms you’re experiencing and the age and condition of your car. For example, if you have an older car with multiple AC issues, it may be more cost-effective to have a professional repair the AC system rather than attempting multiple DIY fixes. On the other hand, if you have a newer car with a minor issue, you may be able to fix it yourself using the steps above.
Frequently Asked Questions (FAQs)
There are a few potential reasons why your car’s AC might be blowing hot air after it gets cold. It could be that there is a problem with the AC compressor, or that the Freon levels are low. Another possibility is that the AC condenser is not functioning properly. If the AC is blowing hot air intermittently, it could also be an issue with the AC switch or relay.
There are a few reasons why your AC may stop blowing cold after a while. One reason could be that the refrigerant in the system is not being circulated properly. The refrigerant is responsible for absorbing heat from the air inside the room and then releasing it outside. The refrigerant that has combined with impurities will not be able to absorb the heat from the air inside the room and the AC will stop blowing cold. Another reason could be that the AC filter is dirty and needs to be replaced. A dirty filter can restrict airflow and cause the AC to overheat. Lastly, the AC may simply need to be serviced by a professional.
It is generally recommended that you recharge your car’s air conditioning system every two years. However, if you live in a hot climate or use your air conditioning system frequently, you may need to recharge it more often. You can check your owner’s manual for specific recommendations.
The condenser decreases the temperature and converts the refrigerant back into a liquid phase. It is responsible for heat loss of the refrigerant when it passes the compressor.
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Im A/c technician from Kahama Tanzania .I like to be asking you some questions on how to troubleshoot some problems concerning AC system.
John Jacob masingili, Yes, I will be happy to answer you.