Car AC blows cold then warm is an annoying issue that no drivers want to face since it causes uncomfortable feelings while driving.
Especially on hot summer days, a cranking air conditioner can make you sweat and drive you mad.
Let’s look for the possible reasons for the problem, thus, find out the proper solutions in this article.
What Are The Reasons For Car AC Blows Cold Then Warm?
A car air conditioner blows cold then warm can be due to several reasons such as a broken valve, damaged clutch or faulty electrical parts, etc.
The most common culprit is a leak in the refrigerant system, causing the AC to gradually lose its cooling power.
It’s advisable to bring your car to the repair shop to have the problem fixed.
The System’s Leakage
When the AC in car blows cold then warm, a small leak in the cooling system is usually to blame for. The leakage is the result of moisture mixed in the refrigerant.
Some people don’t pay attention but add more of this substance every year, creating even more internal moisture.
Since there’s a lack of liquid refrigerant, the air conditioner can’t work properly. Moreover, the combination with moisture is a great environment for corrosion.
The corrosive acid created can harm the valves, hoses, and seals. The worst case is the inside of your AC compressor is also affected, leading to metal fragment spread, blockage, and damaged components.
Faulty Expansion Valve
A faulty expansion valve is the second possible reason why the A C in car blows cold then warm. The expansion valve reduces the refrigerant pressure and allows evaporation.
If the part is blocked, you may experience restricted or too unrestricted refrigerant flow (also known as flooded evaporation.)
The mechanical parts become too cold due to a slight restriction; even ice or frost can be built inside; thus, the warm air comes out.
The “flooded” situation occurs when too much flow doesn’t make the air cooler but also blows out the heat. The puddle under your car can assist the mechanic in analyzing the issue, so make a note of it.
Broken Compressor Clutch
When your AC goes cold then hot, you may want to think of the defective compressor clutch. The clutch is in charge of providing the compressor with the engine power.
The transfer process can be affected if the component is not in good condition.
The clutch gets wear and tear due to time consumption, making it difficult to maintain the perfect clutch gap. The on-and-off cycle is now intermittent. Therefore, you feel the cold and warm air.
Blown Fuse And Wiring Issues
Why does my car ac blow cold then warm? The cooling system consists of many electrical parts; so, it’s understandable that the blown-out air is abnormal when something goes wrong with the fuse or wire.
For example, once there is an unexpected high voltage in the circuit, as a gatekeeper, the fuse may block everything, and the AC shuts off.
Corroded Relay
There’s a coil in the relay responsible for attracting the contacts and connecting the high amp circuit.
When this coil is degraded, its internal resistance grows. The relay will stop the current as the heat rises, causing hot air to come out.
Discharged Battery
A discharged battery or faulty generator means a low voltage level is produced, making the compressor coil struggle to activate.
Besides, the high compressor’s coil resistance can lead to clutch disengagement. Therefore, the car air conditioning blows cold then warm.
Defective Drain Pipe
The air conditioner stops blowing cold air for a while because of a blocked drain pipe.
As mentioned, make a note of the water under your car; it can be a leak of condensed water caused by a blocked evaporator through the drain pipe to the outside.
Overfilled Refrigerant
Knowing how to recharge your car’s air conditioner with refrigerant is very important. When you have the refrigerant overcharged, you’re likely to have the problem of the car air conditioner cold then warm.
Filling the AC system with too much of this substance causes high-pressure refrigerant, turns off the AC high-pressure switch, deactivates the compressor, and leads to the intermittently working function.
Damaged Sensor
The car AC temperature sensor is part and parcel in operating the cooling function. It senses the temperature and sends information to the module to turn on/off the air conditioner.
If the component is broken, it will affect the whole system.
Slow Blower Fan Speed
Slow blower fan speed can also leave you with the car A C blows cold then warm. The low blowing speed makes the refrigerant freeze up, lending a cold temperature inside the evaporator.
In turn, the temperature sensor sends information to the module, and the module decides to block the cold from coming out.
Bad Control Switch
Why does my car air conditioner blow cold then warm? A bad control switch may be another culprit. Normally, you press the switch to turn on and turn off the feature.
However, the contacts are bad, and you’re unable to control the system.
How To Fix When The Car AC Blows Cold Then Warm?
Make Diagnosis
Bringing your car to an auto repair shop is a highly recommended option to deal with the interrupted air-blowing problem and other AC issues, such as car AC stopping working when it’s hot outside.
They can make a diagnosis for your vehicle to find out the exact reason.
It would be of great help if you could help them list out the answers to the following questions, so they can work on solving the root cause when the AC blows cold and then warm.
- Do you feel the warmth from one vent or all of them?
- How long or how far were you driving prior to the problem?
- How many times have you experienced this discomfort?
- Under what conditions does the situation happen? (highway or street road? etc.)
Evacuation
My car AC blows cold then warm. If this is because the air conditioner system is overcharged, evacuation will help you get out of the vicious cycle when. To do so, you need to prepare an air vacuum pump kit and a recovery tank.
Here are the steps on how you can do it:
Step 1. Open the valve to allow the nitrogen to come inside the tank.
Step 2. Attach the vacuum pump. At the same time, you open the valve. Don’t touch anything, and let the pump do its job to remove all the moisture and air. The process will take about one hour.
Step 3. After closing the valve and pump, hang the manifold gauges.
Step 4. Link the low-pressure side to the blue connector and the high pressure to the red one.
Step 5. There are two yellow manifold connectors. You should connect one with the AC recovery unit and the other to the exit port.
Step 6. Open the blue valve on the recovery tank, then the blue liquid valve on the gauge. Watch out for any leakage during the process.
Recharge The System
After evacuating, you need to recharge the system. Before that, if you’ve found any leaks, you should have them covered. Let’s say your leak is small; go for an AC leak sealer. Make sure you choose the correct type.
But when the leak is more serious, let the professionals do it for you. It can cost from $300 to $1500, depending on the severity level of the damaged parts, which is a reasonable price to rescue you once the A C blows cold then warm.
Change The Radiator Fan
Supposing your car AC blows cold then hot when you drive at a low speed, replacing a radiator fan is an ideal option. Some cars have one fan operating at different speeds; some have two radiator fans.
In case you have a dual fan, one should work at its maximum speed. If it doesn’t work, you can’t have the coolness continuously.
Check whether one or both fans run when you turn on your AC. It’s advisable to take your car to a garage for diagnosis and repairs.
Pay Attention To The Condenser
That the AC blows cold then warm can be cleared by working with the condenser. Since the component lies behind the grille, you should try to clean it.
Look for any debris or blockage and have it removed. The build-up of dirt on the AC condenser also explains why your car AC turns on and off randomly.
The cleaning process may help without the need to replace the parts fully. However, it’s a temporary solution. You’d better go for a replacement as soon as possible.
Conclusion
There are many reasons for car AC blows cold then warm, such as the faulty evaporator, clutch, or electrical components.
The best way to have the cooling function work properly is to check in an auto repair shop regularly. Thus, you can say goodbye to your horrible time with a defective cooling system.