Repairing Car Air-conditioning (Part 1)


The Air-conditioning system of one's car started to blow hot air or one found frost in the evaporator. What went wrong? This Part 1 of the article describes how car air-conditioner works and what special equipment will be required to carry out the necessary inspection and repairs.


1.. How difficult to troubleshoot and repair?
If you are not a handyman type, it could be difficult as one might have to dismantle the mechanical components, and might have to crawl underneath the car to carry out the necessary inspection and repairs;

2. Do I need special tools and equipment?
Yes. One would need at least high and low pressure gauge to perform simple work such as inspecting if there are enough gas in the system and charging up the Freon;

3. What other material required?
To top up the Freon, one would need a small tank of correct type of Freon, either R12 for the older cars or R134 for the newer cars. There is also a need to have the special grade of compressor oil ready in hand. To repair the air-conditioning, one would need to have a vacuum pump besides having the necessary replacement parts and the O-rings to seal the joints and pipes. As for the Professionals, they may have owned also the flushing and the Freon recovery system.

4. Can I DIY these special equipment also?
Yes. There are websites that describes how to DIY these equipment using simple and cheaper equipment but proper equipment is required for those serious mechanic who would want to do a good and lasting repair job.

How Air-conditioning works
Air-conditioning works primary on the principle of evaporation. Much like humans feeling the cooling when water evaporates from their skin; except, in air-conditioning equipment. the evaporation process is carried out at very very much faster rate.
The media being used in most air-conditioner or the refrigerator alike is a gas called Freon. Older car used Freon R12 which has now been phased out by Freon R134 because the latter is ozone depletion free.

The air-conditioning system for the car has about 6 major components as shown attached. The cooling process starts at the compressor. The Freon is first compressed from gaseous state to liquid state to a pressure of about 90-180 psi (600 -1200kPa), depending on the cooling requirement and the ambient temperature. Freon gets heated during this compression process and must be cooled by a fan(usually electrical or mechanical) in the condenser (the heat rejection). The liquid Freon, after being filtered by the filter/dryer, will expand quickly into the evaporator through a metered orifice called the expansion valve. This sudden expansion of the liquid Freon into a bigger evaporator chamber causes "violent" evaporation of Freon. This expansion process turns Freon from liquid state to gaseous state and picks up the heat from the car compartment (the heat absorption). The gaseous Freon is then sucked back into the compressor at pressure of about 30 psi (200 kPa). The cycle then repeats.

The Special Tools and Equipment

I) The Basic and Must Have Equipment
1) High/Low Pressure Gauge with Manifold
a) The tool is as shown below
The gauge has the following components
a) 2 pressure gauges, one for measuring high or Freon discharged pressure (red in color) and the other is for measuring the low or Freon suction pressure (blue in color)
b) A manifold with 2 control valves to close the release the Freon gases
c) 3 connection hoses, one to connect to the compressor outlet and the other to connect to the compressor inlet. The yellow one is for connection to the Freon gas tank.

2) Freon
The Freon is usually sold in cylinder tank of about 25 lbs in weight. The commercial ones come in industrial cylinders whereas the hobbyists may buy them in canister.

The Must Have Equipment for Repair Work
1) Vaccum Pump
One would need the vacuum pump to remove the air as well as water vapour trapped in the air-conditioning system after every repair job. Air and water vapour not only taking up unnecessary space, they are harmful also to the compressor. Normally, water will boil at room temperature of 25 degreeC when the vacuum pump reduces the system pressure to 25 mm of Hg. The vacuum pump should be left long enough (15 to 30 minutes) to remove all possible traces of moisture.
Vacuum pump should be capable of pulling at pressures twice the boiling point of the water or around 1 atmospheric or 760 mm or 29” Hg pressure.

2) O-rings and Replacement Spares

Faulty parts are often replaced than repaired. This is because many parts are not repairable. When purchasing replacement spares from the shops, ask also for replacement O-rings. Discharge the old O-rings as these are often deformed after use.

The Professional Must Owned Equipment
1) The Air-conditoning Flushing System
The purpose of flushing is to remove oil and debris in the system. Very often when compressor seized up, it generated a fair amount of metal chips or debris which are trapped in the system, especially in the evaporator. If these debris are not removed, they will damage the replacement compressor.
The Professionals are seen to own and use such a piece of machine because the machines are not only expensive and also require frequent maintenance. The non-Professionals often do away with flushing totally or just flush them with mineral spirits or just petrol, utilizing compressed air to charge in the liquid as well as to dry and empty the cleaning fluid.

The Regulatory Equipment
1) Freon Recovery Equipment
Some countries, like the United States, have mandatory requirement for Freon to be recovered in order not to pollute the environment; however, many other parts of the World, especially in 3rd World and Asian countries. Mechanics have been seen to vent the Freon into the good air.

The Professionals Verse Non-Professionals
In countries that do not regulate car air-conditioning repairs, one would often find many non-professional setting up shops offering different rates for their services.
These non-professionals do not necessary offer lower rates for the repair and servicing work; however, their work can do more harm than good to the car air-conditioning system. It is also good to be aware of such repair shops.
These shops often do not own the necessary equipment such as the flushing system. They also never renew their old and broken down tools and equipment. Many a time, one would find the pressure gauges with broken glasses, tubes full of grease and dirts and vacuum pump with either broken down pressure gauge or without any pressure gauge at all.
These non-professional would often ignore oil losses when charging the Freon and one would not normally realize until the compressors started to make noise a few months' time; by then, a replacement is required.

The author have been often "cheated" by these non-professional shops and therefore, writes this article for the benefit of the car owners

Other Related Sites
1. Car Aircon Compressor Repairs
2 Car Air-conditioning Part 2

3. Car Air-conditioning Part 3
4. Car Freon Charging for Novice
5. Car Safety Inspection and Check at Home
6. Replace Engine Oil by Vacuum
7. Wheel Alignment Using Sideslip meter


Anonymous said...

Mentioning of third world countries venting to the atmosphere reminds me: the mechanics in the US did that before we learned F12 was harmful to the atmosphere. We even went too far in forcing anyone whose system needed a small charge (due to minor leakage) to have their entire system rebuilt. That law was later revised when they realized that EVERYTHING would eventually leak, especially automobiles with rubber hoses! The laws of physics prevails!

Mikes said...

If you are not a handyman type, it could be difficult as one might have to dismantle the mechanical components, and might have to crawl underneath the car to carry out the necessary inspection and repairs; I completely agree to that.

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Casey Jones said...

I was hoping this would be an easy job that I could do at home. Once you started mentioning the need to dismantle things and get underneath the car, I knew it wasn't a job for me. I don't have any real experience working on cars. I will have to take my car in I think to get the AC looked at.

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