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What is the proper refrigerant charge for this A/C system I’m working on?

By: Richard Hawkins, MACS Contributor

That is a question that comes up countless times when doing mobile A/C work. 

When working on a car, light truck or SUV, it is a question that typically has an easy answer. Looking at an A/C decal under the hood, owner’s manual, or checking your information system will usually provide that answer. However, in a small percentage of cases, it can be an elusive piece of information. This information is still highly important, needed to properly service those vehicles.   

Mobile A/C Scenarios

Some examples would be:

1. An aftermarket rear system was added with no refrigerant capacity provided.

2. A vehicle originally with a 6 MM “piccolo” condenser was replaced with a parallel flow unit. This requires reducing the charge and the supplier of the parallel flow condenser does not provide any charge reduction information.  

Both of these condensers fit the same applications: Ford light trucks.  
However, there is a difference in their construction.  The unit on top is a 6 MM “piccolo” unit and uses round tubes.  
The unit at the bottom is a parallel flow unit and uses flat tubes. 
As a result, the parallel flow unit holds less refrigerant. It is necessary to reduce the refrigerant charge when replacing a 6MM unit with a parallel flow.

3.  A heavy duty piece of equipment that has no A/C charge information on it. The manufacturer is also unable to provide any charge information.

Finding a Resolution

I had a recent discussion with someone where a question had come up surrounding a similar mobile A/C issue. It did not involve any of the examples previously stated and had an interesting twist to it.  I do not recall what the vehicle was, but it was a type of SUV. It had originally come with a front and rear system. The rear system was blocked off with an aftermarket “block-off” kit.  

A commonly used mobile A/C “block-off” kit.

The easy answer to this question seemed simple. Check the specification for that vehicle with a single system and use it. The vehicle, however, is only offered with a dual system. Even with a specification for a single system, it would not have been entirely accurate. This is due to it being blocked off near the rear evaporator. With a liquid line and suction line still in place, running all the way back to the rear of the vehicle, these lines will hold some refrigerant. Using the specification for a single system, it would not work because that would result in an undercharge.

There is no doubt there are people out there reading this who might encounter these situations from time to time.


Let’s hear what you do when faced with these situations.  

Please send your responses to:

In a “follow-up” article we will compile the answers and provide the information needed to assess these issues. This will be an anonymous post.  Thank you for your participation in advance!

One response to “What is the proper refrigerant charge for this A/C system I’m working on?”

  1. Pam says:

    What have you done when faced with these situations? Please share your experience. We will compile all answers in a follow up article. We would love to hear from you. Please email to

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