Your car’s air conditioning system relies on a series of interconnected components that move the refrigerant through the system to take away heat energy and lower humidity inside your cab. When a car’s AC starts to struggle, a lot of people jump to the assumption that it’s simply low on refrigerant and they need to recharge it.
Though all too often, people recharge their car’s AC only to find it still isn’t blowing cold air afterward.
So what gives? If it’s got a full dose of refrigerant and then some, shouldn’t your AC be working?
The unfortunate truth is that if your car was low on refrigerant before, it was likely due to a leak, and your best efforts at recharging it will be futile until the leak is repaired. However, it could also be other faults, such as a compressor motor failure or a blockage in the condenser. All of which can be tricky to diagnose on your own.
To help you figure out what’s keeping your car from blowing hot air even after a fresh refrigerant recharge, we will have to look closely at how a car’s AC system works.
How Does a Car’s AC and Engine Cooling System Work
The refrigerant flow in your car’s air conditioning system is driven by a pulley powered by the serpentine belt. The refrigerant moves in its gaseous state through a series of lines to the condenser by the car’s radiator.
The condenser dissipates heat energy from the gaseous refrigerant via a series of cooling fins with help from the radiator’s cooling fan. The refrigerant then starts to cool and reverts to its liquid state. At that point, it passes back through a return line through the drier and past an expansion valve, where it changes from high pressure to low.
From there, the refrigerant fluid passes through the evaporator, where a phase change causes it to boil inside the lines. The fan in your car’s blower motor/heater core blows the cold air chilled by the phase change in the evaporator into the cab. The cold air passes over you with a sigh of relief as the now hot refrigerant is drawn back to the compressor, where the cycle repeats to provide you with constant cooling.
What Type of Refrigerant Is Used in a Car’s AC?
You might be surprised to hear that three different types of refrigerant are used in automotive air conditioning systems. Not all are compatible with each other. So, using the wrong one in your recharge could prevent the AC from blowing cold air.
1. R134 Automotive AC Refrigerant
R134 automotive AC refrigerant is typically only used in cars that were made before 1994. It’s less efficient at transferring heat energy and can potentially damage the ozone layer when it leaks. It should only be used in cars that were made before 1994.
2. R134a Automotive AC Refrigerant
R134a is technically Tetrafluoromethane (CF3CH2F), which is more efficient at transferring energy than R134. If it leaks into the atmosphere, it’s also less likely to cause damage to the Earth’s ozone layer. Though it’s not entirely harmless.
To that point, the European Union has banned its use in all new cars since 2011. The United States followed suit by banning it in all new cars starting with the model year 2021.
It’s often the preferred replacement refrigerant for recharging cars made before 1994 rather than using the original R134. However, the reverse isn’t true.
3. R1234yf Automotive AC Refrigerant
R1234yf is the updated successor to R134a in all new cars starting with the model year 2021 in the US. It performs very much like R134a regarding efficiently transferring heat energy. Its advantage is that it breaks down much faster in the upper atmosphere with little to no impact on the Earth’s ozone layer.
It was also engineered to be compatible with slightly older cars with R134a air conditioning systems. However, the reverse is not true. If your car’s AC is engineered to run on R1234yf and you attempt to recharge it with R134 or R134a, the change in refrigerant pressure may result in evaporator freeze-up on pressure control systems, reducing system airflow. It would also be a violation of EPA regulations!
Common Reasons Why a Car’s AC Isn’t Blowing Cold After a Recharge
Aside from using the wrong refrigerant in your recharge, the most glaring reason why a car’s AC isn’t working is a leak in the system that’s allowing a massive amount of refrigerant to escape. Other mechanical faults like a bad pulley wheel on the AC compressor, a worn-out serpentine belt, or a clog in the condenser could also cause your AC to run hot despite a full recharge of the correct type of refrigerant.
1. A Leak in the System
Even a small leak in a car’s AC system in one of the lines, the condenser or the compressor, can allow your recharged refrigerant to escape, causing it to stop blowing cold air. This is the most likely reason, as vehicle air conditioning systems don’t “Use” or “Burn” refrigerant.
For you to have been low enough on it in the first place to need a recharge, there had to be a leak already somewhere. If it was a major leak, the recharged refrigerant could escape in less than 24 hours. However, even a minor leak might depressurize the system within a few days of heavy use.
How to Find a Leak in Automotive AC Lines
Finding a leak in the car’s air conditioning lines can be frustrating. First, you’ll need to ensure there is at least a modest level of refrigerant in the system. This might mean partially recharging it first.
The bush-fix way to find the leak is to spray soapy water all over your car’s AC lines while the air conditioning is running on max. If it’s in an obvious spot and the leak is significant, you’ll see the soapy bubbles where the leak is.
However, they do make a special tool that’s essentially an electronic nose that you can use to “Sniff” around the air conditioning system. Buying on your own is prohibitive, but some hardware stores and tool rental agencies might let you borrow one for an afternoon for a small fee.
2. A Bad Serpentine Belt
A badly worn-out serpentine belt could leave your car’s AC compressor so underpowered that it can’t blow cold air, even when properly recharged. In such a case, you’d likely hear screeching and whining sounds when you start the car or accelerate hard.
If the serpentine belt is so badly compromised that it can’t power the car’s AC compressor, it likely will also struggle to power other belt-driven components. You’d likely notice the engine running hot due to a weak water pump circulating engine coolant, and the car’s battery would be low from the alternator being unable to charge it properly.
If your car has a traditional reinforced rubber serpentine belt, you’d likely see cracking, fraying, and smoothing of the teeth underneath. However, a newer EPDM serpentine belt doesn’t easily show signs of wear and will need to be tested with a belt wear gauge to confirm it as the reason your AC isn’t blowing cold air.
3. A Stuck Pulley
It’s also possible for your AC compressor pulley to wear out and get stuck, preventing the car’s AC from functioning properly. The symptoms here can be similar to a slipping or bad serpentine belt, with some minor deviations.
The car might make a screeching noise at start-up and when accelerating hard as the belt skids over the stuck AC compressor pulley wheel. However, the other belt-driven components, like the water pump and the alternator, would still function normally.
You’d likely also see signs of burnout on the surface of the pulley. The wheel would also be very hard to turn manually with the engine off. If you let a stuck pulley problem like this go for too long, it will prematurely wear out the serpentine belt as well.
4. You Recharged with the Wrong Refrigerant
If you assume that all automotive AC refrigerants are the same and use the wrong one for your car, it could foul up the system, preventing it from blowing cold air. While the state-of-the-art refrigerant R1234yf is reverse compatible with older vehicles, using R134 or R134a in a car designed to use R1234yf will likely result in evaporator freeze-up on pressure control systems, reducing system airflow.
In such a situation, you’ll need to remove all the refrigerant from the system via a vacuum pump. It’s not safe or recommended for the system to let it leak out of the AC systems independently.
5. A Burned-Out Compressor
If your car ran on low refrigerant for a long time, with the AC on max, it could have burned out the compressor long before you recharged it. In a scenario like this, the refrigerant simply can’t move through the system and won’t go through the pressure phase changes needed to produce cool air in the cab. The blower fan will still turn on but will blow warm engine bay-temperature air.
In a case like this, it’s usually a leak in the AC compressor housing itself that lets refrigerant out in the first place. When you recharge it, the fresh new gas seeps out of the same old hole. If the compressor isn’t completely dead, it might even make a grinding or high-pitched whirring noise right after you recharge it and turn it on for the first time.
Unfortunately, there’s no quick fix for a burned-out AC compressor, and it needs to be replaced. This can cost anywhere from $750 to $1,200.
6. Debris Overheating the Condenser
If you recharge your AC and it blows cold air for a few minutes before gradually turning warm and weak again, debris might be around the condenser, causing it to overheat. Leaves, dead bugs, and other detritus that make it past the grill can gradually clog around the AC condenser, making it hard for it to dissipate heat to the point that it can’t initiate the phase change needed to blow cold air into the cab.
In such a scenario, the air conditioning might blow air for a few minutes and then seem to shut down. The engine temperature gauge might also start to climb, as the debris will also affect airflow in the engine bay. Then, when you turn the car off and let everything cool down, the problem repeats itself.
Canned air or a shop air compressor can be used to spray away loose debris without having to poke and prod around the delicate condenser lines. If this doesn’t remedy the problem, then the reason your air conditioner isn’t blowing cold air is elsewhere.
7. A Clog in the Condenser
If there’s a clog in your car’s AC condenser, your recharged refrigerant won’t be able to circulate through the system to make the phase change necessary to blow cool air. The blower fan in the heater core will simply blow out cab or engine bay-temperature air.
The real problem here is how the clog got in the condenser in the first place. The most likely source is a damaged piece of the AC compressor passed through the lines until it got to a narrow pinch point in the condenser. This would mean your AC compressor is also about to go out as well.
Though it’s possible that the leak in the AC refrigerant lines that let the gas out in the first place also allowed airborne debris to be sucked into the system, since the lines in the condenser are the narrowest, it’s simply the most likely place for something to get caught. Though this is the case, the leak in the lines elsewhere in the system is also severe and needs to be repaired/replaced before your car’s AC has any hope of blowing cold air again.
The easiest layman’s way to determine if there’s a blockage in your condenser and where is to trace the coolant lines in the condenser with an infrared thermometer.
8. A Bad High or Low-Pressure Switch
Another possible reason why your car isn’t blowing cold air even after recharging the refrigerant is a failing high or low-pressure switch. There’s a sensor designed to monitor the pressure and state of the refrigerant as it passes through the high and lower-pressure sides of your car’s air conditioning system with a shut-off switch on both the high- and low-pressure sides.
These switches are essentially safety devices that will disengage if there’s a problem to prevent damaging the compressor or other system components.
If you recently recharged your AC refrigerant without first testing the level, the overly high-pressure condition in the lines could trigger the switch to shut it off. This will prevent the refrigerant from cycling, and it won’t be able to blow cold air in the cab until the switch is reset and the pressure in the lines is corrected.
Each switch must be closed to complete an electrical circuit, which runs to the car’s AC compressor. If either the low-pressure or high-pressure switch is open, it won’t complete the circuit. Without the necessary power, the AC compressor’s clutch doesn’t kick on, and the pulley from the serpentine belt won’t be able to power the system.
How to Test a High- or Low-Pressure Switch
The simplest way to test a high or low-pressure switch in your car’s air conditioning system is to bypass the switch in the electrical circuit with a little piece of wire in the electrical connections. This is basically forcing the switch to close and complete the circuit.
Test the high-pressure switch first with the wire inserted and the air conditioning system turned on. If the system turns off again or the AC compressor clutch disengages, then the assumption is that the low-pressure switch is failing. Repeat the same test bypassing the high-pressure switch. However, testing the switch with a multimeter is probably safer if you have one handy.
9. A Bad Ambient Temperature Sensor
A lot of modern vehicles with interior climate control systems have one or more thermostats that can fail, causing the car not to turn the AC on and off when needed. If one of these “Ambient Temperature Sensors” is caked with dust, it might not turn the AC despite there being adequate refrigerant in the system.
Most ambient temperature sensors are installed in the headliner above the passenger or driver’s side seats. Even if you can’t access the sensor, you might be able to vacuum the headliner clean and reset the sensors via the following steps.
This will reset the sensor, and the AC should blow cold air again as the recharged refrigerant cycles.
Frequently Asked Questions
How Do I Test My Car’s Refrigerant Levels?
Some cars have viewports or a little window in the receiver/dryer area that lets you see the AC system’s refrigerant in action. If you don’t see anything or a bunch of little bubbles, you should be suspicious that you have low refrigerant.
To accurately test your car’s refrigerant levels, start by finding the low- and high-pressure ports of your AC system’s Schrader valves. Then, attach the gauges to the low-pressure service port and the high-pressure service port.
Start the engine with the air conditioning system on its coldest setting and Let the car run for at least 5 minutes to ensure the system is fully cycling and any refrigerant in the system is in motion.
Check the pressure on the gauges. You should see a reading of 25 PSI to 45 PSI on the low-pressure port and a reading of 250 to 400 PSI on the high-pressure port. If both readings are below this range, then you are likely low on refrigerant.
How long does it take for the AC to get cold after recharge in a car?
Once you’ve recharged the refrigerant in your car’s AC system, expect the production of cold air to commence without delay. The system should attain peak cooling efficiency within approximately 5 to 15 minutes of running time. This interval is not set in stone and may slightly vary from one vehicle to another, though the variation is typically marginal.
The fresh refrigerant is distributed throughout the AC system throughout this period, initiating the cooling process. It’s recommended to keep the car running with the AC on the maximum cool setting to complete this process.
Conclusion
If you recently recharged your car’s refrigerant levels, but it’s not blowing cold air, then you likely have a leak in the system that’s letting the refrigerant out. Especially since these are sealed systems that don’t burn or use refrigerant, they only cycle them and change the pressure.
Sometimes, you can find the source of the leak by spraying a soapy water solution around the AC lines and components. If you see bubbles while the AC is cycling, then you’ve found the source of the problem.
While you’re poking around the engine bay, take the time to check the tightness of the serpentine belt as well as clear any debris from around the condenser. While the system is running for the soapy water test, you can also trace the lines in the condenser with an infrared thermometer. If you spot any massive areas where it suddenly changes from hot to cool, you likely have a clog inside the condenser itself!
You might also want to try giving your headliner a quick vacuum before resetting the ambient temperature sensor.
These are all simple things that you can do to help dial in why your car isn’t blowing cold air. From here, you’ll have to dive into more complicated diagnostics like testing the high-pressure switch, which might require the services of a professional mechanic.
Written By
Jason Farrell
Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.