Quick Check/Topping Up a Car's Air Conditioning.





After getting the car back from the AC service guy, I wanted to perform a quick check and if necessary, a minor top up on the refrigerant. Ideally the car AC should be evacuated then refilled by measuring the mass of refrigerant. This vehicle takes 23oz but I didn't want to do that in case there is a hidden leak in the system. Evacuating with a leak will contaminate the AC system: always find and repair a leak first!

Car AC systems are always a tricky thing to work on if the mass measuring method is not used and if there are leaks. For this job I assume no leaks and follow a rule of thumb I have used several times on different vehicles. So far my quick top up method works fine but I again I highly recommend complete evacuation and mass measured refill.

A r134a recovery station can be use to reclaim the refrigerant if an evacuation is to be done. In my country there is absolutely no restrictions for this type of refrigerant. If you live in a country with legal restrictions then by all means follow the law. In my case I am allowed leeway. So with all that legal stuff mentioned, read on as I performed this task.

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Step 1: The Tools.

My tools are:
Digital refrigerant manifold Guage set.
Digital thermometer.
R134a can, 12oz.
Can tap.

I set the thermometer sensor into a vent and left the display on the dashboard. This way I can easily read the vent temperature from outside the car.

Step 2: Hooking Up the Guages.

Only the low pressure port is used here. Once coupled up I turned on my digital Guage.

A special note here. When the r134a can is hooked into the manifold yellow hose, I turn the valve on the cap tap to allow a small flow of refrigerant. I then turn on the blue valve on the manifold to flush air out through the blue hose. Next I couple the hose to the port on the car and turn off the blue valve at the manifold. This way there is zero air contamination.

Step 3: Starting the Car.

I ran the engine with the AC on and the blower on the lowest setting.

Step 4: Checking and Topping.

The lowest temperature within ten minutes was 4.7C which is good. Typically the vent temperature can go a bit lower so I opened the can tap valve and slowly opened the low pressure valve on the manifold. Once the pressure Reading went near 20psi I shut the valve off. I watched the thermometer and repeated the process 3 more times.

The lowest temperature reached 3.7C which is much better. Also at this point the pressure reading climbed to 20psi quickly when I open the manifold valve, which is an indication that the AC system is near its proper charge. I don't want the low pressure port to read 20psi or beyond at idle speed due to risk of overcharge.

Now the car AC blows quite cold in our tropical heat. Wife is quite happy and so am I.

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    5 Discussions


    3 years ago

    remember that you need to be certified with the EPA to perform these repairs.

    4 replies

    Reply 3 years ago

    I believe the author is from Trinidad. It is not under US jurisdiction. Your advice is true for anyone living in the US and its territories.


    Reply 3 years ago

    Thanks for the backup and info. I am from California in the US and you can't even put gauges on any device unless you're either certified or being overseen by someone who is HVAC certified. I just don't want anyone to get in trouble.


    Reply 3 years ago

    Coincidentally my son is a HVAC technician. Some refrigerants displace oxygen and can cause damaging freeze burns on the skin.Some refrigerants also contain CFC's and could damage the ozone layer. Some refrigerants do require certification to buy and to work with it. Yours is a valid concern!


    Reply 3 years ago

    Actually people can buy 134a Freon recharge kits to charge their vehicles without any certification most anywhere. Every auto parts store I've ever been to sells such kits all day long. Now it you are servicing vehicles for a living, then I think you do have to be licensed and certified. But I can walk into even WalMart and buy 134a Freon any day of the week without issue. JMHO