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How to Test and Recharge Your Car's Air Conditioning Unit

Dec 8, 2017

recharging your ac unit in your car

How to Recharge Your Car’s AC Unit


You know your car may be ready for a charge when the summer comes around, and you turn your air conditioner on, and it never gets cold.  Typically, a car may never need to have it’s AC unit recharged for over 100k miles or more depending on how often you use it or what sort of climate you live in, but in general, you’ll know something is up if, after your AC has had a few minutes to start working, if the air coming out of it never gets cool and refreshing.  


Many mechanics will trick or try to convince you that you need this service or that your car is due for this service while you’re getting a tuneup or oil change.  Don’t be intimidated.  If you’re happy with the temperature of the air coming out of your car’s AC unit then you’re fine.  It's really that simple.  Nothing bad will happen to your car if it's run out of "cold air" so don't stress.  It doesn’t need to be charged on any particular schedule- it can wait for you to decide you want cold air again.  


However, warm air from your AC unit can also indicate a bigger issue, such as a leak that may need to be repaired, but you can figure that out pretty easily.  If you charge your car’s AC, and a few days or weeks later the air coming out of the unit is no longer cold, it’s time to take it to a mechanic.  If you charge your AC and the air continues to stay cold, you’ll know it was just time to add more refrigerant to the system. 


The first way to see if your car is low on refrigerant you can acutally stick a meat thermometor into your car's AC vent and put it on full blast.  If the temperature of the air is in the 40's-50's even after the car has warmed up, its possible your car is low.  You can also start initially by checking to see if your compressor is engaging.  The AC compressor converts the refrigerant in your car from liquid form to gas.  When your AC is on high, the compressor should be spinning.  If you turn it on full blast and the compressor is not engaging, then the issue may be bigger than just a simple recharge, such as an electrical issue or compressor failure.



How to recharge your car’s AC Unit:


1. Get your refrigerant system: At any auto store you’ll find a guide that tells you exactly what refrigerant recharger you need to purchase.  The AC chargers basically look like mini fire extinguishers with hoses and gages on them.  You check the guide out to make sure you purchase the correct system.  


ac refrigerant for cars


2. Check the refrigerant pressure: Before charging your system, you want to check the pressure.  Turn the vehicle off and locate the low side pressure service port in the engine.  The cap will usually have an “L” on it. 


You take the hose attached to the recharge canister and gauge and place it right over the pressure service port.  Do not pull the trigger.  At this point you’re only looking to get a reading, not recharge your car. 


Restart your vehicle and make sure the AC is on the highest setting.  Watch the gauge on the refrigerant hose and check to see if your pressure is under 40 psi.  If it is, your system is under-charged.  You want the reading as close to 40 psi as possible. 


3. Charge your car’s AC:  ALWAYS make sure you follow the specific directions on the AC charging system.  In generally they usually work the same way across the board, but never assume and always double check. 


Attach the refrigerant can onto the recharge hose if it’s not already.  Once the can is installed hold it upright and pull the trigger for 5-10 seconds to add refrigerant to your vehicle.  After charging for 10 seconds, check the PSI again to see how close you are to 40 psi.  The car will still be running while charging.


4. Repeat until you are as close to 40 psi as you can get.  You do not want to over charge your system, so be very careful. 


5. Double Check: To double check your AC is charged correctly, you can use a meat thermometer and stick it right into your car’s AC vent in the interior of your car.  Fully charged, the air temperature can be as cold as 28 degrees, but may vary slightly. 


6. Keep an eye on your car’s temperature.  If a few weeks go by and your car’s AC stops blowing cold air, it may be time for a professional to take a further look to see if there is a leak or bigger issue with your system.  

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