Top Up of R134a Refrigerant.




Introduction: Top Up of R134a Refrigerant.

The wife's car came back from the AC repair guy but the performance in cooling has been lackluster. Since only the compressor connections were removed to facilitate repair of the clutch, I tested for leaks at those 2 connections. It is critical to identify and repair leaks on all air conditioning systems.

The best and most accurate way to charge any refrigeration system is to measure the mass of refrigerant put into an evacuated system. Typically cars take anywhere from 21 to 23oz of r134a refrigerant. Always consult the service manual for the vehicle to be certain.

The cheaper way is to measure line pressure and blower air temperature while adding refrigerant. For cars I use a limit of 20psi on the low pressure line, measured with my digital manifold.

The danger of the quick method is the risk of over charge. Too much refrigerant in Oz, even by a small excess, will damage the compressor very quickly!

Read on for how I did a top up to improve my wife's car air conditioning. Note that in my country no license or permit is needed to handle or purchase refrigerants.

Step 1: The Tools.

The tools needs are;

-digital manifold gauge set.
-can of r134a.
-can tap.
-digital thermometer.
-r134a adapter.

Step 2: Checking for Leaks.

Using a thick solution of dish washing liquid and water, I brushed this onto the 2 connections at the compressor. No popping bubbles were noticed so it is reasonably leak free.

Step 3: Hooking Up the Manifold.

With the can tap connected to the yellow hose, I turned on the can tap valve a little to get the air purged out then I turned on the blue valve. I quickly connected the blue hose with adapter onto the low pressure port. Next I turned off the blue valve on the manifold.

The red or high pressure valve remains closed for this job.

The r134a can must stay upright for the job.

The high pressure line is not used for Topping. It can be monitored for diagnosis purposes but never to enter refrigerant into the system.

Step 4: Adding Refrigerant.

With the car started and AC compressor on, recirculation mode, blower fan on max, I measured the vent temperature after idling for 5 minutes. Only 4C below ambient which is terrible. The digital thermometer sensor I stuck into the driver side air vent.

I slowly opened the blue valve to allow r134a into the system. Keeping an eye on the low pressure gauge, I made sure to shut off the blue valve when the pressure climbed to 20psi. I left the engine on idle the entire time. I had to gently shake the can of r134a to get the gas into the system. Patience is needed here to add r134a and let the system equalize then add some more. This will take some time.

Step 5: The Desired Temperature.

Ideally the air vent should be at least 10C below ambient on a hot day. I kept adding refrigerant till I achieved that value.

When the system got close to the required charge, the pressure climbed quickly to 20psi when I opened the blue valve. This is a good indicator that no more refrigerant is to be added.

Beyond 20psi carries the higher risk of overcharging so that is why I don't go beyond that. If I'm not careful, even at 20psi the system can be overcharged but once the temperature at the vent is low enough, my job is done.

Step 6: Completion!

This car has 2 blowers and with both enabled, the lowest driver side vent temperature is below 10C. The pressure at that temperature is in the second pic.

With only the front blower on, the temperature and pressure are shown in the last 2 pics. Inside at the rear of the car was quite cold.

In all this took half hour to ensure the pressures throughout the system were at steady state values.

I hope this instructable has been helpful to you my readers.

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    3 years ago

    Thanks mate I'll just have to get a digital meter set now !