The author, who operates an automotive service instructional and consulting firm based in Fort Washington, Md., does on-site auto service training that includes a review course on refrigerant recovery and recycling.
As a professional automotive trainer, you would think that from all the classes that I have attended, and all the other trainers I have talked to and all of the shops I have visited, maybe, just maybe someone would stop and say, ``Hey! That doesn't sound right to me!''
I've been a technician for 24 years, and a trainer for 15 of those years. And I'm still waiting to hear that said.
Case in point:
I have heard of technicians using compressed air (shop air) to pressurize an air conditioning system in order to check for leaks.
Hello-o-o. . . (See me knocking on the tech's forehead repeatedly, with several pauses in between. The first pause was to see if I got his attention. The continued knocking was to see if he really understood what he was saying.)
So let me understand this-someone is using the same shop compressed air that goes through the pipes that run up and down and sideways on shop walls. The same pipes that should have drain cocks every four feet on the pipe. The same shops with temperatures (this IS air conditioning season, isn't it?) ranging from 90 to 125 degrees.
Just a wild guess. But there is a remote possibility that we could have just a small amount of condensation-read that ``water''- in those pipes.
Unfortunately, this is really happening somewhere in the field every day.
I've gathered the correct information for proper leak testing of an A/C system, backed up by data from two well-known air conditioning organizations about why using compressed air in any air conditioning system should never be done.
In order to test the A/C system for leaks, use your recovery/recycling equipment to recover any refrigerant in the system. Vacuum the system down to at least 27 inches of vacuum for a minimum of 30 to 45 minutes.
Put your vacuum process on hold for two minutes. Then, by using your A/C gauge set and vacuum pump, while the pump is still running, shut off your low side gauge first-the high side is already closed-and then the pump. Hold for two minutes.
If the system pressure rises above 27 inches of vacuum, there is a leak in the system, or your equipment connections could be loose.
If no vacuum leaks are present, then proceed to add enough refrigerant to the system to show at least 50 pounds of pressure or more in order to perform a proper leak test with an electronic leak detector.
Using that detector, circle all of your connections, go over all of the components thoroughly, and don't forget to leak-test the HVAC case inside the vehicle.
The following two sources of information underline why compressed air should never be used to pressurize any air conditioning system:
The International Mobile Air Conditioning Association's (IMACA) Mobile Vehicle Air Conditioning Retrofit Manual cautions that, in reference to CFC-12 refrigerant, shop air should not be substituted to leak-check an A/C system.
IMACA said shop air can introduce dirt, moisture, oil and other contaminants into the system.
IMACA also warns not to substitute high-pressure nitrogen, as this may result in equipment damage or personal injury due to a component rupture.
Nitrogen may be absorbed into the lubricant and behave like a non-condensable gas when the system is running, showing higher system pressures and resulting in poor performance.
Dupont's ``Safety of Suva Refrigerants'' bulletin (H-27350-3) notes that because the physical and chemical properties of HFC-134A are very similar to CFC-12, most of the safety considerations apply to HFC-134A.
But there is one important difference between the two materials: Both are non-flammable at ambient temperatures and atmospheric pressure. However, tests under controlled conditions have indicated that, at pressures above atmospheric, and with the air concentrations greater than 60 percent by volume, HFC-134A can form combustible mixtures.
An ignition source is required to initiate combustion. In this regard, the product behaves in a similar manner to HCFC-22, which is non-flammable but also combustible at pressures above atmospheric in the presence of high air concentrations.
The tests indicate that HFC-134A can undergo combustion at lower pressures than HCFC-22.
Under no circumstances, Dupont cautions, should any bulk storage, cylinder fillings, equipment charging, or refrigerant reclaim or recovery system-or any A/C or refrigeration system-be pressure-tested with air/HFC-134A mixtures.
So, shop owners and managers, do yourself and your technicians a favor and please have signs printed with this important information. Then post it.