11 Reasons Your Car Air Conditioner Blows Cold Then Warm

Car Air Conditioner Blows Cold Then Warm

Usually, when AC is turned 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. While you are on a long route in a cool car and suddenly realized that your AC started to blow hot air, then you for sure there is an underline reason for the car 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 blows cold and then warm.

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Car Air Conditioner Blows Cold Then Warm

Women Cooling Herself
Women Cooling Herself

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 air conditioner blows cold then warm. Here you will find the complete reasons of a car AC blows cold then warm then cold again.

11 Reasons For Car Air Conditioner to Blows Cold Then Warm

Below are the eleven complete reasons for a car air conditioner blowing cold and then warm.

  1. Moisture In The AC System
  2. Blocked Drain Pipe
  3. Blocked Expansion Valve/Orifice Tube
  4. Defective Compressor Clutch
  5. Refrigerant Overcharged
  6. Discharged Battery
  7. Blown Fuse
  8. A Corroded Relay
  9. Faulty AC 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 blows cold then 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. This contaminated air contains vapors that start to freeze up near the expansion valve in the evaporator and the refrigerant circulation is stopped. Thus, warm air starts to blow. 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 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

AC Drain Pipe
AC Drain Pipe

A 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 not allow air to bypass until ice melts and cold air returns, which results in, the car AC stopping blowing cold air after a while.

3. Blocked Expansion Valve/Orifice Tube

Expansion Valve
Expansion Valve

The cold air process starts with the expansion valve. It decreases refrigerant pressure and gets it cooled. Contaminated refrigerants such as metal particles, debris, and sometimes ice build in the valve, which keeps the expansion valve or orifice tube stuck in a closed position 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

Car Compressor Clutch
Car Compressor Clutch

An AC compressor clutch is used to transfer engine power to 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

AC Overcharge With Refrigerant
AC 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 AC is turned ON, it blows cold air at first, but soon the cold air turns to warm air because of the high-pressure refrigerant, shuts off the car AC high-pressure switch, resulting in the car AC sometimes working sometimes doesn’t.

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6. Discharged Battery

Dead Battery
Dead 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 to energize the compressor coil.

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

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 air conditioner to blow cold 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 air conditioner to blow cold and then warm.

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9. Faulty AC Control Switch

AC Switch
AC 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

Blower Fan
Blower Fan

Low blower speed can also cause the refrigerant to freeze up in the evaporator. 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.

This is an Info
Make sure the blower fan must run at least for the first ventilation to remove enough cooling from the evaporator to protect it from freezing.

11. Bad Sensors

Car AC Temperature Sensor
Car AC Temperature Sensor

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.

Frequently Asked Questions (FAQs)

Why does my car AC randomly blows hot air?

There are a few potential reasons why your car’s AC might be blowing hot air. 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.

Why does my AC stop blowing cold after a while?

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. If the refrigerant is not being circulated properly, it 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.

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


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    About The Author

    2 thoughts on “11 Reasons Your Car Air Conditioner Blows Cold Then Warm”

    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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