Air conditioning repair

People who work on their own cars should be able to repair the air conditioner. While working on my B.S. I had to take physics classes that covered gases and refrigeration so I understood the dynamics of air
conditioning. However, theory didn't help me when the air conditioner on my 1978 Ford Granada stopped blowing cold. I mentioned my problem to a mechanical engineer and he pointed out all the components on my car. He suggested adding freon (back in 1980 a 12 oz can of freon was 50 cents or so) into the low suction side. I did that but the air still wouldn't blow cold. My co-worker told me to buy a manifold gauge set and measure the low and high side readings. After I bought the gauge set I noticed that a special adapter was needed for the high side fitting so I bought one from JC Whitney and took the readings. Ray said that the high side reading looked low and to try adjusting the expansion valve. I did that with a friend sitting in the car watching the temperature thermometer and the air conditioner went to 40 degrees.
Since that day in 1980 I have always been able to repair my air conditioner.
When the compressor howled and screeched due to a bad bearing I had to evacuate the system and another co-worker showed me how to do it. I bought a vacuum pump and pulled 30 inches of vacuum and found no leaks with the new compressor. I put the freon back in with no harm to the ozone layer.
One Spring day I turned on the air conditioner and had no cold air. I suspected that one of the O-rings dried up during the Winter so I connected the gauge set and found hardly any high side pressure. I connected the vacuum pump and found I couldn't pull a vacuum. I checked the O-rings at the compressor, expansion valve, and hoses and found the dried one. I replaced every O-ring with new ones, pulled a vacuum, and put in new freon.
When the 20 year old high pressure hose burst I simply replaced both hoses, pulled a vacuum, and put in new freon.
While working for a different company a young technician mentioned that his air conditoner wasn't working. I told him that I do all the work on my air conditioner and could look at his. I brought my gauge set to work the next day and connected it to his system. I thought his high side was too low so we drove to Kragen and bought 2 cans of freon and charged his system. He was so happy when the temperature gauge went to 35 degrees. I tried to explain how every component worked and the basic theory of gases and refrigeration but I'm not sure how much he understood or cared. I found out later from other employees that he was impressed with my knowledge of air conditioning. I hope that he was able to work on air conditioners since then.
I also know why the government wanted only trained individuals to work on automobile air conditioners. Before freon was banned a local NBC affiliate in Los Angeles showed a typical gas station working on an automobile air conditioner. The illegal immigrant Mexican was loosening the high side pressure hose and the second the system was opened the freon escaped into the atmosphere in a cloud of white gas while the high pressure hose whipped back and forth.
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I haven't owned a car yet that had an adjustable expansion valve.
And system pressures are almost useless except if your looking for gross problems like a completely plugged line. What you are looking for is measuring the temp differential between the freon going into and coming out of the different parts of the system. The pressures are very much affected by variables like humidity, air temp, temp inside the car, outside the car, etc. Some manuals do have tables of pressures that list the major affecting variables, these are somewhat useful.
And you also should not add freon to a system lacking a sight glass like this. The by the book procedure is to completely evacuate the system. Then refill the system with the designated volume of freon the system was designed to hold. You can also try adding refrigerant gradually until the temp differentials are where they are supposed to be, of course this only works if the system is in running order.

In all of the cars I've owned when the A/C compressor had problems it self-destructed throwing junk into the freon lines. I'd have loved it if only a bearing in the compressor failed.

Pretty inefficient when you can use an electronic freon leak detector to find the leak. And if you pull apart a sealed joint to replace an O ring the joint may not reseal correctly. Better to only mess with the joints that are leaking.
Many cars also do not use o-rings they use flared fittings.

Your lucky. Sometimes when hoses leak like that they lose bits of the hose into the freon line which will plug the screen on the expansion valve.

The explanation of how the AC system works is in the factory service manual It's also on the backside of the recharge kits in the auto parts store. This young tech was no tech if he thought he could repair anything without reading the manual.

The government wants trained individuals to work on R12 systems due to the environmental contamination. They don't care if idiot techs do shit like this with R134a systems since R134a sales are not restricted. Further R134a is used as an expansion gas in foam insulation, and a propellant in asthma inhalers. Those sources dump hundreds of tons of R134a into the atmosphere every year, dwarfing that produced by leakages from auto A/C systems.
You may know the theory but you seem to lack practical experience in current repair techniques. You would probably benefit from spending some time reading many of the online sources out there for that. You might also benefit from reading the EPA regs covering A/C work. The fact you didn't mention sight glasses or electronic leak detectors has me wondering.
Ted
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On Mon, 18 Jun 2007 00:52:33 -0700, "Ted Mittelstaedt"

poisonous gas by thermal decomposition.
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