11 Reasons Your Car AC Blows Cold Then Warm & How To Fix It

Car Air Conditioner Blows Cold Then Warm

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 on a long route and suddenly realized that your A/C started to provide heated 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

Women Cooling Herself
Women Cooling Herself

An automotive air conditioning that emits 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 A/C 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 A/C 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 A/C to blow cool air and then warm.

  1. Moisture In The A/C System
  2. Blocked Drain Pipe
  3. Blocked Expansion valve/Orifice Tube
  4. Defective Clutch Of The Compressor
  5. Refrigerant Overcharged
  6. Discharged Battery
  7. Blown Fuse
  8. A Corroded Relay
  9. Faulty A/C Control Switch
  10. Slow Blower Fan Speed
  11. Bad Sensors

1. Moisture In The AC System

Freezed Ice Cubes
Freeze Ice Cubes

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 A/C 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, heated 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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This is an Info
The main reason, the moisture needs to be removed from the A/C system is to prevent it from freezing up, which blocks the refrigerant movement. Because water has a freezing point of 32 degrees Fahrenheit, but the refrigerant freezing point is -142 degrees Fahrenheit.

2. Blocked Drain Pipe

AC Drain Pipe
A/C 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 it 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 from getting bypassed until the ice melts and cold air returns, which results in, the car A/C stops blowing cold air after a while.

3. Blocked Expansion Valve/Orifice Tube

Expansion Valve

The Chilly 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 A/C blows cold and then warm.

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4. Defective Compressor Clutch

Car 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 clutch of the compressor is subjected to wear and tear, which forces it 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 A/C compressor works intermittently.

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5. Refrigerant Overcharged

AC Overcharge With Refrigerant
A/C Overcharge With Refrigerant

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 A/C is turned ON, it emits chilly air at first, but soon the cold air turns to heated air because the high-pressure switch shuts off the compressor clutch, as a result, ac run at different speeds.

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6. Discharged Battery

Dead Battery
Dead Battery

The battery provides voltage to the compressor coil to attract the clutch of the compressor 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 A/C starting cold and then getting warm.

7. Blown Fuse

Visual Inspection Of Blown Fuse
Visual Inspection Of 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 A/C to blow chilly air and then warm.

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8. A Corroded Relay

Corroded Relay
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 A/C to blow chilly air and then warm.

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9. Faulty AC Control Switch

AC Switch
A/C Switch

A faulty A/C control switch can be the reason for vehicle A/C emitting heated air. The car A/C control switch turns ON and OFF the air conditioner. A bad A/C control switch that will not make good contacts can also be the reason for the car A/C blowing cold then warm then cold again.

10. Slow Blower Fan Speed

Blower Fan
Blower Fan

You can face this issue if the fan isn’t working. Because enough amount of cooling is not removed from the evaporator. As its temperature drops too much, the A/C temperature sensor sends signals to the A/C control Module to stop the AC. Which can force the A/C to stop emitting cool air after a while.

This is an Info
You must make sure at least one time that the blower fan runs for the first ventilation to remove enough cooling from the air direr to protect it from freezing. Fans are important for exchanging heat therefore most vehicles have two radiator fans.

11. Bad Sensors

Car AC Temperature Sensor
Car A/C Temperature Sensor

The car’s electrical sensors provide important information to the A/C control module to turn ON and OFF the car A/C. Sometimes, a bad temperature sensor, a bad control module, or a sun load sensor can also lead to car A/C intermittent cooling.

How To Fix When The Car Air Conditioner Blows Cold Then Warm

There are a number of possible reasons for the A/C blowing chilly air 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 A/C system. If they are low, you may need to consult a professional auto repair to refill the system using an AC recovery unit.
  • Inspect the compressor, condenser, and expansion regulator for any visible damage or clogs. Also, check the valve on the recovery tank. If any of these components are faulty 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 heated air.
  • Check for any A/C leaks and make sure you choose an 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 A/C 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 A/C 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)

Why does my car AC randomly blows hot air?

There are a few potential reasons why your car’s A/C might be provides heated air after it gets cold. It could be that there is a problem with the A/C compressor, or that the Freon levels are low. Another possibility is that the condenser is not functioning properly. If the A/C provides heated air intermittently, it could also be an issue with the A/C switch or relay.

Why does my AC stop blowing cold after a while?

There are a few reasons why your A/C may stop blowing chilly air 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 A/C will stop blowing chilly air. Another reason could be that the A/C filter is dirty and needs to be replaced. A dirty filter can restrict airflow and cause the A/C to overheat. Lastly, the A/C may simply need to be serviced by a professional.

How often should you recharge your car AC?

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 refill it more often. You can check your owner’s manual for specific recommendations.

What is the function of a condenser?

The AC 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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    About The Author

    2 thoughts on “11 Reasons Your Car AC Blows Cold Then Warm & How To Fix It”

    1. John Jacob masingili

      Im A/c technician from Kahama Tanzania .I like to be asking you some questions on how to troubleshoot some problems concerning AC system.

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