Before opening access to any refrigerant in a system, read the most current regulations of the Environmental Protection Agency in the Clean Air Act section 608, regarding the venting and/or recovery of refrigerants.
Most home and office air conditioning uses the HCFC-22 with 410a emerging as the dominant refrigerant.

An exceptionally brief look at the REFRIGERATION CYCLE OF OPERATION: 

A discussion of the cycle of the refrigerant in the system could easily 
take weeks or even months for you to have a comprehensive understanding of it. 

BUT! Don't panic! 

We are going to take an awfully brief look at it and hope it is enough for you 
to control the refrigerant charging (placing of refrigerant into the system) and 
maybe even identification of problems. I will attempt to make it easy for you. 
Remember that we are not wanting to be technically correct or make you an expert. 
We want to "get you by" safely and effectively between visits from your professional 
person. 

Everything contains HEAT: 

You must understand that we are dealing with heat, the heat that is contained in
everything--air, water, Freon®(refrigerant), concrete, etc. It is stated in technical
circles as fact that ice is not cold but rather it contains less heat than our body 
does, so we call it cold. Technical thought states that it is holding less heat than 
our body is holding. So if you can see heat in things in this way you can better 
understand a measurable difference they have. There may be 68°F difference between 
the heat of our body temperature (98.6°F) and the amount of ice (32&176;F). 

If you place some small piece of frozen "thingy" that is 200°F below zero in a 
vat of ice, then the ice is HOT to the "thingy", and it will quickly absorb some of 
the heat from the ice and it will "thaw". I hope you understand the importance of all 
this as we later explore the amount of heat in a refrigerant even though it is at a 
temperature of 45°F. It could not absorb much heat from 65°F air passing 
over it, but it could absorb a lot more if the air blown over it is 90°F. 

Refrigerant TEMPERATURE and PRESSURE vary directly: 

This means that if you keep a can of refrigerant-22 sealed and the temperature of 
the air around it is 95°F., then the pressure inside is going to be 184 pounds. 
At 40°F, it is only 69 pounds. As you warm it, the pressure increases and as 
you cool it the pressure decreases (if it remains sealed in a container). Also, if 
you pump it up in pressure then the temperature of the refrigerant will also increase. 
Look at the charts showing this pressure/temperature relationship. 

Refrigerant looks like WATER: 

If you look through a "sight-glass" into a container of refrigerant, you will see a 
liquid or a liquid and some vapor that looks just like water--clear and fluid. Very 
different from water, though, if you open the container, the refrigerant will zip off 
into space as a vapor. It does this for two reasons: 

It is under considerable pressure. 

It boils at any temperature above MINUS 38°F unless it is kept in a sealed container; 
thus, it boils instantly and vaporizes as soon as it is not under pressure. 

Reducing the pressure of refrigerant will cause it to absorb a lot of heat: 

If you were to deliberately spill some refrigerant on the floor, it would immediately 
vaporize, but in doing so it would absorb a lot of heat from that spot in the floor and 
the surrounding air. The floor would become cold. 

If you flow refrigerant through a small tube and then through an orifice into another 
tube, but much larger, then the refrigerant would vaporize (boil) and absorb a lot of 
heat (the tube would feel cold). Did you ever place your thumb over a water hose and 
try to seal off the end from the flowing water? Didn't you get a fine mist that sprayed 
into the air? Remember how cold it felt and how little of it hit the ground. It vaporized 
and as it did. It absorbed heat from the surrounding air as it vaporized. This is what 
refrigerants do inside the tubing of the evaporator coils as air blows over it. 

If the compressor pumps the refrigerant to a higher pressure, the refrigerant gets HOT: 

If pressure increases, temperature increases. If your compressor raises the pressure of 
the refrigerant to 275 pounds inside the condenser coils, the tubing will get HOT because 
the temperature of the refrigerant rises with pressure. The compressor as well adds a lot 
of heat because it uses a motor and mechanical pressure to make the refrigerant pressurize, 
however, we have to pressurize it to get it to flow through the tubing at a great pressure, 
so we can orifice it and reduce the pressure in the evaporator to get the "cooling effect". 
Then it absorbs a lot of heat from inside the room and the compressor "sucks" it back to 
start the cycle again. 

As refrigerant absorbs heat, it increases in pressure inside the EVAPORATOR: 

The high-pressure refrigerant goes through the orifice (flow control device), vaporizes 
and rises is pressure again. The system is designed to keep that pressure just right, though, 
so that the temperature of the vaporizing (boiling) refrigerant will remain above 32°F 
and somewhere below 55°F. That is "cold" enough to absorb a lot of heat from an 80°F 
room air flowing over the evaporator. If it were below 32°F, then any moisture that it 
causes to condense on the tubing would freeze on the tube, and that would be detrimental. 

A lot of it would even restrict the air flow through the evaporator and would actually 
insulate the tubing so that it slowed the boiling of the refrigerant on the inside of the 
tube. So the equipment manufacturer designs it to be above 32°F., it will blow just 
enough air over it, with just enough cooling coil surface, with just the right size of 
flow restrictor (orifice) to drop the temperature of the air going past it about 20°F. 
If an 80°F room air passes through the evaporator, then it comes out the supply 
grills at about 60°F. 

It is designed so well that a lot of "the cooling effect" is still left in the refrigerant 
as it returns back into the compressor and this cools off the hot motor windings and 
mechanical parts just before it gets compressed again to start the new cycle though 
the system, however, it is designed so well that no liquid is left to dump into the 
compressor, because liquid will not compress and it would break the valves inside the 
compressor. You see, now, that the pieces all have to fit together just like the manufacturer 
planned it. 

Too much refrigerant or too little would prevent that "just right combination" from happening. 
Thus the refrigerant "charge" must be right, the parts must be working and they must be kept 
clean to do the job. 

To check the refrigerant action and level of charge, you will need a set of refrigeration 
gauges and manifold. If you do not have a set (Know more about them), there are still many 
things you can check and do to discover if your unit is working well. 

A good thermometer, though, will be essential. You will use it all over the system. You must 
have one that can be taped to the copper tubing without breaking. 

The first thing to use it for is checking the temperature of the air going into the indoor 
blower. Then check the air just inside the nearest supply air opening. The air coming out 
of the supply duct will be approximately 20°F. below the temperature of the returning 
air to the equipment. 

If your cooling coil or filter or blower wheel are downright dirty, then the difference in 
temperature will probably be higher. This means you may have substantial generation of cooling, 
but not enough air to get it from the cooling coil into the rooms. You may also be close to 
having icing of the cooling coil (evaporator) and your electric bill will be higher. 

Check these conditions to make sure they are clean. Read the section on filters if you have 
not done so, for this will be the cause of this dirty condition. If these things are dirty, 
they will have to be cleaned before you can do very many other things for the diagnosis of 
problems. 

If the evaporator coils are dirty, don't just brush them off and think you've gotten them 
clean. It's the stuff trapped inside the fins within the layers that will be a problem. 
You will have to have a service technician remove the coils, clean them and reinstall them 
for you. This may cost as much as $350.00 to $800.00, but it will have to be done, but it 
will be worth it to you in the long run. After the cleaning, use the best filter you can 
acquire for future operation. 

If you checked the temperature of the air into and out of the indoor unit and the differential 
is low, say 12°F versus the optimal 20, then you may have a cooling generation problem. 
The first thing to check now is the cleanliness of the outside units coils. 

Refer to the precautions on the home page and turn off the power (the 230 VAC supply) to 
the outside unit. Reread the first page on Condensers, if necessary, in order to make sure 
the power is truly off. 

You won't be able, most likely, to tell if the coils of the condenser are dirty just by 
looking. You will have to use the garden hose and spray into the fins of the coil and 
watch the other side to see what comes out. You may indeed see a bunch of stuff you didn't 
expect to see. If there is the slightest amount of clogging of the coil, then continue on 
to give it a very appreciated bath. 

You may have strong water pressure, and you will have to avoid hitting the fins at an angle 
to prevent them from being damaged by the water. Spray vigorously, though, and give it a 
thorough cleaning. Don't just stand back and sprinkle it a bit and think it is clean--it 
won't be. Look over into the unit and watch the mud come out. Make sure the leaves inside 
the condenser haven't accumulated to the point of restricting the flow through the coils, too. 

Let it drip dry for a half hour or so and then you can turn it back on to check the 
temperatures again. Let it run for at least 10 minutes or more before you check these 
temperatures. If you got a lot of matter out of the coils, it will do wonders for the 
operation of the system. Recheck things now.