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Don’t overlook a diagnostic clue

By Richard Hawkins, MACS contributor

Make sure you don’t overlook a diagnostic clue! When thinking about the topic of A/C diagnostic tools, a recovery, recycle, recharge machine (R/R/R machine) is not one of the first tools that comes to mind.  It may not come to mind at all in the world of inexperienced technicians. 

However, it is something that can provide some valuable information.   Yes, knowing how much refrigerant is recovered from a vehicle can be very useful information.  It can indicate why a system is behaving the way it is (maybe an overcharge, or undercharge), and it can also tell us if a system might have a leak.

Consider a scenario like the following:

A shop does some work on a system with let’s say a 20-ounce refrigerant capacity. They charge the system with accurate charging equipment.  It is performing flawlessly; the vehicle is released to the owner, and they are very pleased.

A week later it comes back in, cooling poorly and symptoms point to an undercharge.

The shop looks for evidence of a leak/leaks and doesn’t see anything.

The refrigerant is recovered, and it is determined there are only 13-ounces in the system.  That is a loss of 35% or about 1 ounce a day, which is significant. The R/R/R machine is not going to tell us where the leak is, but it tells us there certainly is a leak and how significant it is. 

When utilizing this information, it is important to be sure that the equipment we are using has the capability to remove just about all the refrigerant from a system and weigh it accurately. Otherwise, we could get an indication that a system was low on refrigerant and in reality the machine left a lot of refrigerant in a system and/or did not weigh it accurately.

This can be determined by looking at the label on the machine. There should be information on the label indicating the SAE standard that the machine meets.  Please see picture #1.

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Picture #1: As indicated on the label, this machine meets SAE standard J2788.

SAE standard J2788 is for R-134a machines and calls for a machine to be able to recover 95% of the refrigerant in a system in 30 minutes or less with no heat applied to the system.  It also calls for an accuracy of plus or minus 1/2 ounce in weighing the refrigerant.  

Most of the machines that meet the standard will recover greater than the 95% and have greater accuracy than the plus or minus 1/2 ounce.  At the bare minimum, a J2788 machine will tell us within 2 ounces, how much refrigerant is removed from a system.   This of course is on a machine that is calibrated properly and the calibration of machines should be checked periodically.

J2788 machines have been around since 2007 and they certainly make up the majority of machines currently in use.  However, there are some older machines still in use and the information from them on how much refrigerant is recovered from a system cannot be used to accurately  determine how much refrigerant was in a system.   Most of the older machines met SAE specification J2210.  Please see picture #2.

Picture #2: This machine meets the older SAE J2210 standard.

R-1234yf machines have different standard numbers but have the recovery capability and accuracy of the R-134a J2788 machines.  Please see pictures # 3 and #4.

Picture #3: This R-1234yf machine meets SAE standard J2843.

Picture #4: This machine meets SAE standard J3030. It is designed to be originally used for R-134a but can be converted to R-1234yf.

Several years ago, I was in a shop doing some preparation for some clinics and conducted a J2210 verses J2788 machine recovery test.

Check back in next week for the results of that test.

Has this ever happened to you with an A/C repair? Let us know in the comments section below.

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