Auto Air Conditioning & Heater Repair: compressor will not engage, nissan sentra gxe, refrigerant lines

Question
My wife just bought a 1997 nissan sentra gxe from a lady she works with and the a/c does not work.  The fan works fine but only blows hot air.  The compressor does not come on at all. When you press the a/c button on the dashboard the light does not come on either.  I have checked the fuse under the dash and another under the hood and they are both ok. Would being low on freeon keep the compressor  from coming on at all?  If you can get me started in the right direction, it would be great.  Thanks

Answer
John,
Absolutely a low charge will prevent your compressor from coming on. If there is little to no refrigerant inside the system, that will open the contacts inside your low pressure switch and not allow your compressor clutch to engage.
Here is an easy way to check...  
With your key in the run position, A/C switch on....
Locate your pressure switch, according to my wiring diagram it is located in the front left of the engine compartment. It will be located on one of your refrigerant lines. It will have a plug on it with a blue-yellow wire and a blue-white wire. Disconnect this plug from the switch. With a small insulated wire, jump the terminals in this plug. As you do this, you should be able to hear your compressor clutch "snap" If it does, all you need to do is charge it up.

Before you charge it though, you may want to think about getting the leak fixed. The A/C system is exactly like the refrigerator in your kitchen. You should never have to charge it up, it is a sealed system. If you have to then you definately have a leak that may have you charging it again before too long. Dependant upon how large the leak is.

I hope this is of some help. Thank you for the question and if I can assist you any more now or in the future, do not hesitate to ask. Good luck in everything and if you found this response helpful please remember to rate this answer.