Car AC Blows Cold Then Warm – Revealing the Possible Causes

Car AC blows cold then warm happens at the time when we need our AC to work at its best which raises several questions among car owners because a functional AC is necessary when driving, especially in hot weather.

Car AC Blows Cold Then Warm

Your car AC blows cold then warm then cold again because of internal faults, such as a broken refrigerant, a discharged battery, and a bad sensor. Defective valves, compressor clutch, and radiator fans may also cause the AC to blow cold air and then hot air.

Read on for more detailed information on these defects in AC systems and their solutions.

What Are the Reasons Why Your Car AC Blows Cold Then Warm?

The reasons why your car AC blows cold then warm is because of broken elements in your car’s AC systems. Issues with the refrigerant, clutch, control switch, fan speed, electrical system, and temperature sensors lead to a dysfunctional AC. A discharged battery and blocked drain pipes also cause this problem.

Identifying and replacing faulty parts should fix the problem.

– A Faulty Refrigerant System

A leak in the refrigerant system leads to the AC blowing hot air. The air conditioner cannot function properly when the refrigerant levels are low. The leak also leads to corrosion, especially when mixed with acid. The mixture corrodes the valves, hoses, and seals, and corrosion in the inside parts of the compressor may lead to blockage and a damaged AC.

An overcharged refrigerant will also lead to the air conditioner blowing cold and then blowing warm air. When the refrigerant floods the air conditioning system, its high pressure overpowers the AC clutch. The overpowered clutch cannot activate the compressor. The air conditioner will malfunction or run at irregular speeds.

– Broken Sensor

The temperature sensor is an essential part of the cooling system in your car. The sensor sends signals to the module to switch the air conditioning system on and off, depending on the car’s temperature.

A faulty sensor cannot send accurate signals when the temperature rises. The cooling system malfunctions until you fix or replace the sensor.

– Faulty Compressor Clutch

The function of the compressor clutch in the AC system is to provide the engine power that the compressor requires to start. The clutch enables the pulley to engage and disengage the compressor’s engine power. The clutch is among the most used parts of the cooling system.

What Are the Reasons Why Your Car AC Blows Cold Then Warm

The normal wear and tear increases the clutch gap. A worn-out clutch cannot sustain the pressure and power the compressor to turn the AC on and off as required. The AC compressor does not control the temperature cycle efficiently.

– Blockages in the Drain Pipe

A blocked drain pipe allows the evaporator to reach into the condenser water, causing it to freeze. The low temperature causes ice blockages in the evaporator.

The refrigerant gas cannot flow until the ice melts, allowing the cold air to flow. Consequently, the AC won’t blow cold air consistently.

– Electric System Issues

The AC system consists of wires, fuses, switches, and relays. All the elements work together to turn the AC on and off. Any fault in any of these parts will cause the AC to start blowing hot air instead of cold air. For instance, the fuse may shut down automatically when a high current flows through the circuit, and the AC goes off whenever the fuse blows.

Corrosion on the relays also affects the AC function. The relay controls the level of current in the circuit, and the coil in the relay wears out with time, causing high internal resistance. The relay cuts off the current flow when the internal resistance is high. The AC stops blowing cold air after a while as temperatures increase because of the corroded relay or worn-out coil.

– Slow Fan Speed

A slow blower fan may cause the refrigerant to freeze, leading to abnormally low temperatures in the evaporator. The temperature sensor sends a signal to the module to prevent cold air from coming out. The air conditioner will be blowing cold air and then warm.

– Defective Expansion Valve

The expansion valve lowers the refrigerant pressure allowing evaporation. If the valve is damaged or blocked, your vehicle will experience unrestricted (flooded) evaporation or restricted evaporation. The result is freezing temperatures that may cause frost or ice on the inside parts.

Defective Car Expansion Valve

The restriction in evaporation leads to warm air out of the air conditioning unit. Flooded evaporation also blows hot air instead of cool air.

– A Dead Battery

The battery supplies power to the compressor coil, which is necessary to activate the compressor clutch. When the battery voltage is low or empty, the battery cannot generate enough power for the air conditioner to operate at its full capacity. Low voltage will slow down the blower fan.

Another problem with low battery voltage is high resistance in the compressor coil. The resistance disengages the clutch instead of engaging, causing the AC to start cold and then warm.

– Faulty AC Switch

Your AC may be blowing cold air and then hot air because the AC control switch is defective. The internal elements of the AC system may be functioning properly. However, a faulty switch will go off before you can achieve the ideal temperature in your car.

Sometimes the switch fails to turn on the AC system unexpectedly. A quick replacement solves the issues if other elements are functioning normally.

– A Faulty Condenser

The condenser expels heat from the refrigerant. Any issue that causes the condenser to stop functioning or operate at a low-performance level will disrupt the cooling system.

Replacing a condenser is expensive. Hence, it is advisable to check it first whenever the air conditioning malfunctions.

How To Fix a Car AC That Blows Cold Then Warm

To fix a car AC that blows cold and then warm, you need to identify the underlying cause. Inspect the car air conditioner first to identify any internal leaks or defective parts. A broken AC system requires evacuation before installing new parts.

– Evacuate the AC System

The best solution to an overcharged AC system is evacuation. If you leave the car in this state for a long time, the high pressure will push the switch to disengage the compressor clutch. Shutting the clutch equalizes the pressure, but the process starts all over again. The car air conditioner remains in a vicious cycle of blowing hot and cold air as the internal system tries to stabilize the clutch.

You can stop the cycle by evacuating the AC system. You can do it home with a recovery tank and an air vacuum pump kit or take the car to a mechanic.

The process of evacuating an AC system is as follows:

  1. Open the valve in the recovery tank to allow nitrogen into the tank.
  2. Connect the air vacuum pump and keep it on as you continue to open the valve. The process removes excess moisture and air from the recovery tank. Keep the pump on for at least an hour.
  3. Close the vacuum pump and valve and then connect the manifold gauges. The low-pressure part goes into the blue manifold connector, while the high-pressure part connects to the red connector.
  4. Attach one yellow connector to the port in the recovery unit and another to the exit port.
  5. Check the recovery tank for a blue valve and open it as you observe the leaks. Release the liquid by opening the blue liquid valve. The valve is on the manifold gauges.

Remember that you can get help from a qualified mechanic if the evacuation process sounds complicated or if you need more tools.

– Recharge the Electric System

After evacuating the AC system, the next step is to recharge the refrigerant systems. Use a leak sealer to repair any leaks before recharging.

Fixing Car AC That Blows Cold Then Warm


The best sealer for your vehicle should help you identify the main source of the leak and seal it with a solid substance.

– Check and Fix the Faulty Parts

Any broken part in the AC system will affect its performance. Identify the specific part that requires repair or replacement. For instance, if the AC compressor valve, control switch, clutch, condenser, fan, or sensor is broken, replace it immediately.

While checking for the broken element, you may identify worn-out but functional parts. Do not wait for an AC malfunction. Instead, buy and install new parts immediately, even if they are just worn out.

– Full Car Diagnosis

Sometimes replacing one part does not fix the AC. The system may develop new issues soon after replacing the faulty part or fail to achieve optimal performance.

Fixing what you can at home is a good start, but driving your car to a mechanic for a full diagnosis is advisable. The diagnosis should be an addition to your regular car service.

Why Does My Car AC Blow Cold Then Warm Causes and Fixes Conclusion

Are the Possible Causes for Jumper Cables Melting Similar to the Causes for Car AC Blowing Cold then Warm?

The popular causes of melting jumper cables may not necessarily align with the causes for a car AC blowing cold then warm. It is crucial to address the specific issues for each scenario. While overheating or improper connection can lead to cable melting, the AC issue might stem from refrigerant leaks, faulty compressor, or electrical glitches. Understanding the distinct causes helps in finding appropriate solutions for each problem.


You can tell from this guide that many problems can cause your car air conditioner to blow cold and then warm, but fixing the problem and running your AC again is easy.

Let us go over the main points covered in the article.

  • Leaks or moisture in the refrigerant system cause corrosion and ice blocks, affecting its function.
  • High pressure in the AC system causes the compressor clutch to malfunction, leading to irregularities in the cooling system.
  • Faulty parts such as a broken sensor, a slow blower fan, a dead battery, a broken clutch, a faulty condenser, and electrical faults cause the AC to blow warm air.
  • Evacuating the AC system and recharging the refrigerant system is necessary to fix the problem with the AC.

You have enough information at your fingertips to diagnose and fix your AC issues. However, involving your mechanic for a full car diagnosis is advisable to avoid recurring issues.

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