Auto A/C Repair 101|A/C Troubleshooting

In previous posts I have covered the basics of how a/c works and different components found on auto a/c units.
Now we can discuss things that go wrong with a/c and how to locate the problems.
By far, most common problem found on the automotive air conditioner is either low in freon or out of freon. Contrary to popular belief freon is not used up by running the a/c. It doesn't wear out or go bad. If your car a/c is out of freon or low in freon ,there is a leak somewhere. If the freon is contaminated, it either came from an outside source or some component has failed.
First off it is almost impossible to properly diagnose an a/c problem without a set of gauges.
Connecting a set of gauges to the system will not tell you if the system is slightly low it will only let you know if there is enough freon in the system to operate. A system that is only slightly low may function fine on a warm day but not satisfactory on a hot day. The gauges will also allow you to see if the compressor is pumping properly or if there may be a blockage in the a/c system, ie clogged dryer or bad expansion valve.
Use care when connecting the gauges to the a/c system, liquid freon can cause frostbite and liquid freon in the eyes can cause blindness.With all this in mind let's do a quick check

• Start the car and turn on the A/C.

• Is the compressor running? If you can see the front of the compressor, the clutch should be engaged and the extreme forward part of the compressor should be turning. Not just the pulley portion, the actual front part is the clutch plate that drives the compressor.
• If the compressor is turning feel the lines at the back of the compressor. The small line is the high pressure side it should feel warm or hot to the touch. The larger line is the suction side and it should be cool to moderately cold to the touch. Also check the lines at the evaporator, the same applies.
• If the compressor is cycling off and on this is a good indication that the freon is probably low.
• If the compressor isn't running at all , check the a/c fuse first.
  

• If the compressor is running and there is no temperature difference or only a slight difference either the freon is low or there is a circulation problem. note: on most newer vehicles if the freon is low the compressor will not run. the low pressure safety switch will keep the compressor turned off.

• With this quick check, if the a/c seems to be cooling but the air inside is not cool, several things come to mind

1. The heat valve may not be turning the water off to the heater core.
2. The dampers in the ventilation ducts may not be operating properly.
3. The evaporator could be clogged not allowing sufficient air flow over the coils.

• If the initial check provided you with the information to conclude that the a/c was not cooling gauges should be connected for further testing.
• Don't just cram more freon in to see if this fixes the problem, remember what I said ,, your a/c does not use up freon, if it is low, there is a leak. Also if something else is wrong, overcharging can cause damage to other components.

Alright , I've got some work to do now. I'll continue our Auto A/C Repair later. If there are any questions anyone has, just ask in the comments and I'll try to help.