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How to diagnose a car Air Conditioner | What to do prior to refilling the AC system with refrigerant

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  • OVERALL DIFFICULTY INDEX: 3/10
  • IF YOU HAVE NO TOOLS YU SPEND $25 TO GET THEM FOR THIS JOB
  • IF YOU HAVE NO EXPERIENCE YOU SPEND 1 HOUR TO CARRY OUT THIS JOB
  • SAFETY: RISK OF INJURIES FROM A PRESSURIZED SYSTEM, SEE BELOW
BEFORE YOU START
  • This pictorial does not cover the way to refill the car A/C with gas refrigerant (freon), rather provides useful tips prior to refilling it wiith the R134a gas, that ensure your car air conditioner will work again for several years of service.
  • The proposed method for releasing the R134a refrigerant into the atmosphere might be illegal in some countries. 
  • Make sure to wear safety goggles when releasing the refrigerant. The R134a has low toxicity but should not be breathed. Is it still classified as a gas with global warming potential. It is safe to ozone layer.
DISCLAIMER:
Our pictorials are of informative nature and do illustrate works carried out by ourselves at our own premises for our own use and satisfaction.
Readers who envisage to carry out similar works inspired by the below method shall do this at their own risks and liability.

Symptoms and diagnostic of an aged A/C in a car

The A/C of your car is no more as efficient as it was?
You just noticed something wrong with your car air conditioner?
​If you car is more than 5-7 years old and that it is the first time this happens, then proceed as follows:
  1. Turn on the air conditioner in your vehicle and place your hand in front of each of the air outlet grilles. 
  2. In case you feel that the air is coming cool enough on one side of the car and still warm on the other, then most likely your A/C just needs to be refilled with refrigerant (freon).
Although A/C systems in cars are hermetic and tight, it is inevitable to have normal but very slow leaks of refrigerant (the gas that allows the system to produce cool air, commonly called "freon") all along the lifetime of your car. 
Depending on how often you turn on your air conditioner (the more the better), such leaks could result in a drop of the refrigerant quantity inside the car AC below the minimum operable level, in a matter of 5 to 7 years typically and up to 9-10 years.
You can diagnose the above in a sure manner with a scanner.
Plug your scanner in the vehicle and go to the page where you can read the A/C refrigerant high pressure:
In normal conditions, the refrigerant high pressure should read 8-9 bars unlike the above readings:
  • 7.4 bars at idle
  • 5.6 bars when driving
The air condioner of this vehicle, aged 9 years has lost enough freon and needs to be refilled, nevertheless and because it did last so many years with no maintenance at all, some preventive maintenance is required like explained below prior to proceeding with the refill of refrigerant gas.
You can also check the blown air temperature by inserting a thermocouple in the A/C outlet as you should read in normal conitions:
  • Lowest: 2 degrees Celsius
  • Highest: 10 degrees Celsius
As a general rule, the below car A/C diagnostic logic can be followed most of the time:
Age of the vehicle
Preferred A/C intervention
< 1 year
An A/C failure denotes a problem. The car is still under warranty; it is a must to claim the warranty and have the AC fixed by the car dealer, especially early failures are costly to repair and result from a sudden leak of the entirety of the refrigerant from the defective part.
3-5 years
Normal A/C drop of performance due to slow refrigerant leaks. The more you use your car air conditioner on daily basis and the more it will last with no maintenance. Once the above described symptoms start to occur,  it is enough to simply refill refrigerant with no other intervention on the system.
5-9 years
Normal A/C drop of performance due to slow refrigerant leaks. It is however recommended to replace all A/C hose seals in the engine compartment prior to attempting a refrigerant refill. This will require to vacuum the system.
​> 10-12 years
It could still be a simple and normal drop in the refrigerant quantity and no more, but it is then recommended to diagnose and test the whole A/C system of your car. In particular check for leaks at condenser and compressor levels, and make sure there's no excess noise generated by the AC compressor. Hoses are to be inspected carefully for traces of oil on the rubber which denotes a leak of their crimped connectors.

Removing the AC refrigerant hoses and identifying the seals

​Find your car A/C valves which look like excatly a bicycle / car tire valve.
Caps do cover them, but once the cap is removed, you will identify the "tire-style" valve easily.
There are two of them, one directly fitted on an A/C tube and the other one on top of a cylinder as shown below.
Use a small flat screwdriver to briefly press on the valve core and check if remaining pressure is still there.
Pull away your head, wear safety goggles and do not breathe the freon that comes out when doing so.
  • If there's no freon at all, then the below described repair won't be enough and you need to go through a thorough diagnostic to determine the source of the refrigerant leak.
  • If a residual pressure is there, then it is time to proceed as suggested below.
Locate the car A/C hoses, there are no more than two of them.
Unscrew the holding nut of the one connecting to the top of the A/C condenser. It is the part that is identical to a radiator and that fits on the car's radiator.
Again, pull away your face while wearing all safety gear and pull out the hose from the condenser with your hand (picture to the right).
This will dicharge the remaining freon into the air. To note that while professional workshops are forbidden to do so due to the large amounts of freon they deal with, it remains indeed exceptional in the case of an individual maintaining his/her car once upon the lifetime of the vehicle.
Use a 3/8 ratchet handle along with extensions as shown below to reach all nuts that do hold the hoses to the A/C compressor and condenser. You will need to remove a total of 4 nuts, since the A/C hoses connect to:
  • A/C compressor inlet
  • A/C compressor outlet
  • Condenser inlet
  • Condenser outlet
One of the two hoses will be completely free and can be removed from the vehicle.
The other one will remain connected to the aluminum tube that goes inside the vehicle and connects to the A/C evaporator.
The purpose of this preventive fix is to replace all seals at the A/C hoses connectors.
Use a small flat screwdriver to remove the freon seals so you can purchase new ones of  matching diameter and thichness.
Until you get the new seals and refit the A/C hoses, make sure to plug the compressor outlets with whatever plugs you find.

Refitting the car A/C refrigerant hoses with new seals

In most cases, the A/C hose connectors seals will consist of silicone O-rings but some use specific cylindrical seals. You can then fit O-rings of the same size from any assortment box available at online stores, unless seals are specific in which case they are to be purchased from spare parts shops from your car dealer.
With your fingers, refit the new seals.
Fit the first one which will sit in the first groove, then add the second one which will cross the frist groove up to the one inside the connector.
Add a drop of oil (any oil) on the new seals and refit / re-connect the AC hoses, tighten their nuts.
You just made sure that your car A/C has been made tight again for several years of service and just needs to be refilled with freon.
A professional workshop typically refills with refrigerant without replacing the seals, which could lead to a less durable repair, so better you make sure this is done by yourself, then go to the workshop for freon refill, which is a quick intervention of less than an hour that is typically charged around 20$ inluding the cost of the R134a refrigerant.

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