How to Diagnose a Non Working Air Conditioning in a Car
Driving around on a hot day in a car without a working air conditioner can be uncomfortable and even dangerous in extreme heat. Diagnosing the reason that your air conditioning isn’t working will help you determine whether the problem is one that you can fix yourself or if you need to take it to a repair shop. You are also less likely to be taken advantage of at a repair shop if you already know why your AC is not working.
Collecting Initial Information
Turn the air conditioning on while the car is running.The air conditioner won’t run properly unless your engine is running. The best setting for diagnosis is “fresh air” (not recirculated) with the air blowing out of the center vents in the dash and the AC turned on.
- Start with the fan speed turned to its highest setting.
- If your car has a “Max AC” setting, select that option.
Listen for unusual noises coming from the AC.Noise could indicate that there is a problem with your compressor and that it needs repair or replacing.
Feel the air coming out of the vents.You will need to know if the air is cold, room temperature, or hotter than the air around it. Also note if it starts cold but turns warmer, or if it is usually warm but blows cold intermittently.
Notice the air pressure.Turn the air pressure to the high and low settings and see if the airflow changes like it normally does.
Smell the air coming from the vents.If there are unusual smells, you could have a leak. You may also need to change your cabin air filter.
Inspect your car’s fuses.Check your owner’s manual for the location of your car’s fuse panel, as it may be under the hood, in the trunk, or even in the driver’s foot well area. A blown fuse can cause your AC to stop working.
Diagnosing Airflow Problems
Check all of the vents.Be sure that air pressure is coming out of the vents that you have selected. Move the vent selector to see if the air moves to the proper vents.
- If changing the selected vent does not alter the flow of air, you likely have a blend door problem, which will require replacing the doors inside the dash that determine the direction of the air flow.
- Blend doors change position when the temperature selection is changed, blocking the flow or permitting the flow of either hot or cold air.
- Sometimes an AC system with a mode door problem could be working fine, but the air flow is being directed somewhere else, like back out to the engine, instead of into the car.
Look at your cabin air filter.Especially if the air coming from your vents smells funny or if you think you have had a slow decrease in pressure for some time, check the air filter. You will be able to see if it has a buildup of dirt or debris on it.
- It is possible that your cabin air filter is so blocked that it is interfering with your air pressure, and replacing it will be a relatively easy an inexpensive fix to your problem.
- Your car manual may have instructions on replacing the cabin filter. If it doesn’t, try searching online for “replace cabin air filter” followed by the year, make, and model of your car (for example, you might search for “replace cabin air filter for 2006 Toyota Camry”).
Check for a blower motor problem.The easiest way to do this is to try turning on your heat. If you have weak air flow when the heat is on as well, your blower motor may have gone out.
- A blower motor may have a resistor problem if your air only blows on the high setting but will not blow on a lower setting.
- Unfortunately, mice and other rodents sometimes build homes in car HVAC hoses and can get caught in the blower motor when the car is started. A loud noise (or bad smell) coming when the heat or air are running could be a sign of this problem.
Diagnosing Air Temperature Problems
Find the front of your AC condenser.It is normally located in front of your radiator. If there are leaves or other dirt or buildup blocking it, remove them and clean the area.
Look under the hood at the AC compressor clutch.If your air pressure is normal but the air is hot, you may have a compressor problem. Checking to see if the compressor clutch is engaging is a simple visual inspection. The compressor is usually located towards the front of your engine, just inside the grill of your car.
- Your car should be running with the AC on to check the compressor clutch.
- The compressor looks like a small motor with a large wheel on the end. The wheel (which is the compressor clutch) should be spinning. If it is not spinning, you have a problem with your compressor.
Check the tension on the belt of the compressor.It should be tight. If it is loose, you need a new compressor belt.
Find any coolant system leaks.One of the most common AC temperature problems is low refrigerant. The AC system is closed, so refrigerant should not be lost unless there is a leak.
- Look for oily residue on or around hoses that attach AC components together. Oily spots may indicate a refrigerant leak.
- You may consider using an electronic leak detector, which can detect much smaller quantities of refrigerant.
- There are also some testers that use dye, UV light, and protective glasses to find leaks.
- If you do find a leak, you will likely need to hire a professional to repair the leak. You will probably need new parts too, as many of the components cannot be repaired or patched.
Check for freezing.If your AC blows cold initially but then stops being cold after some use, it could be freezing. Excess air and moisture in the system may lead components to freeze (literally).
- Freezing can also be caused by an oversaturated receiver/drier or accumulator.
- Turning the system off for a while and letting it thaw will temporarily solve the problem.
- If the problem is persistent, you may need your system to be flushed or evacuated with a vacuum pump.
QuestionMy truck heat works; it defrosts, but only on 3 and 4. It only blows hot air on 3 and 4. I've put coolant in it, and it works for a few seconds, then stops. I checked for leaks, and it doesn't have any. What can I try next?wikiHow ContributorCommunity AnswerA blower motor may have a resistor problem if your air only blows on the high setting but will not blow on a lower setting.Thanks!
QuestionWhat do I do if I had the vacuum pulled and my a/c unit charged on my truck, but it is still blowing hot air?wikiHow ContributorCommunity AnswerThere are other components that could also be bad. A recharge will only fix your system if the charge was low. If you have no leak and a fully charged system but only hot air then it could be the compressor, a relay, orifice tube clogged or another component. See a technician for advice.Thanks!
QuestionCan a blown fuse box cause your AC not to work?wikiHow ContributorCommunity AnswerSure, if the fuse that feeds your AC compressor or relays is blown and not delivering +12VDC you will have no AC.Thanks!
QuestionWhat do I do if my A/C isn't blowing air?wikiHow ContributorCommunity AnswerPossibly either a fuse or the blower motor isn't working. Check the fuses under the hood, and check under your glove compartment for a cylinder shaped motor. With the A/C on, gently wiggle the cord to test for a short in the adapter. If this doesn't work, then you can use a fuse tester to see if your blower motor is getting power.Thanks!
QuestionWhat if smoke comes from the vent when I turn the a/c or heat on in my car?wikiHow ContributorCommunity AnswerIt's probably water vapor, not smoke. This is entirely normal, especially in humid environments. Unless it smells or doesn't dissipate, don't worry about it.Thanks!
QuestionHow do I diagnose a 2008 Crown Victoria police model with no air conditioner or heat?wikiHow ContributorCommunity AnswerThere could be a problem with your blower motor. Check the associated fuse/relay, and then diagnose the motor itself via physical inspection.Thanks!
QuestionI have a 2005 G6, and the AC button will only light up when the vent circulating button is on. This button also won't turn off unless the fan is not on at all, and there is not cold air blowing for the AC. What could be wrong?wikiHow ContributorCommunity AnswerCheck to see if your AC clutch is engaging. If not, you could have a bad compressor or fuse; check the fuse first.Thanks!
QuestionThe air conditioner in my car will only blow air on the highest setting, and the temperature changes between cool and warm. What could be wrong with it, and how much would it cost to repair?wikiHow ContributorCommunity AnswerFirst, Replace the Blower Motor Resistor (easy fix, this part is likely located under the glove compartment of your vehicle). Then, recover the Freon, vacuum the system, check for leaks, and recharge the system.Thanks!
QuestionThe AC air blows cool air while driving, but in stop-and-go traffic it will blow warm air. What could it be?gourav prasadCommunity AnswerThe car AC pumps cool air at an RPM of 1500+, so in order to get the cooling, you need to maintain an RPM of 1500+.Thanks!
QuestionI have a 2002 Camry 2.4L 4 cyl. If my AC compressor breaks, can I still drive the car?wikiHow ContributorCommunity AnswerYes, but you well need to see a mechanic to fix a smaller belt for you. Before driving it, with the compressor broken, you will not have access to use your AC.Thanks!
What would cause high pressure on the low pressure side of the A/C in a car?
My AC doesn't work, and makes a weird sound when I turn it on. What could be the problem, and how can I fix it?
How do I fix a broken center fan in my car?
On very hot days, after my car sits in the sun, my a/c and radio lose all power. Then it sits overnight and it works in the morning! What could be the issue?
What is wrong if the temperature dial is causing my A/C fuse to blow on my car?
- Do not add refrigerant unless you are sure that low refrigerant is the cause of the problem because overfilling the system with too much refrigerant can cause severe damage.
- It is always best to consult a professional to do repairs to your vehicle.
- Wear safety glasses and work in an open environment, where fumes won’t overwhelm you. Never touch your eyes or mouth after handling Freon or other chemicals. Wear long sleeves and gloves whenever possible.
Sources and Citations
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