i bougt the car last week and have to fix a few things; ac being one of them.
my friend who i bought the car from told me that the freon leaked out after he got into a car accident.
what i wanted to know is what should i look for and know about the AC before i go to a mechanic and get ripped off?
also can anybody recommend a trustwrthy mechanic to fix the AC in Brooklyn NY?

 

I'd recommend the forums at ackits.com and aircondition.com for the a/c service recommendation. The guys there really know what they're talking about.

 

I'm used to domestic R134A systems and I have not had a chance to really look over the system on the Maxima yet. However if he got into an accident and the refridgerant leaked out, chances are the main culprit is either the condenser which sits in front of the radiator or there is a cracked/punctured line somewhere near where the accident damage was. Once you determine where the main leak is, you'll need to replace the damaged components(s).

Let's assume it's the condenser. You would need to change the condenser and the associated O-rings for those fittings. A new drier / liquid tank should be installed along with an orifice tube / expansion valve. Depending on the system, oil needs to be added to a new drier in the proper amount. PAG oil is one type of A/C oil, but it does vary depending on the manufacturer.

Once that is done, the system should be fully evacuated with a vacuum pump for 45-60 minutes. Once evacuated, you'll need to monitor the vacuum on the system for a couple of hours to make sure it's not leaking down. If you lose vacuum then you've still got a leak. If a leak is found, you may need to put some dye into the system and check with a UV light or use a leak detector that can sniff out leaks. Once the system is confirmed leak free, gauges need to be installed and some R134A should be added. Engage the A/C system and add refridgerant until the high and low side pressure is within spec. Most often if a system is out of freon, the compressor will engage and then disengage right away to prevent damage. As you add R134A, the compressor will start cycling less frequently.

A/C work can be quite complicated. There are several custom tools that you need to do the job right. If you don't do the job right, you have the potential of damaging the compressor and/or other components.

Also any A/C system that you really don't know the condition, you should open up and flush. Check and make sure the compressor operates correctly and is free of any abnormal noises. If you find any metal shavings in the system, it's a bad thing and each component will need to be flushed. Some components once clogged cannot be flushed and need to be replaced (example would be the evaporator and condensor in some vehicles).

Good luck.

 

Its most likely the condensor as stated. Not a hard thing to change, did mine in june. First check components ie. compressor/condensor/line's etc look to be in working order and not cracked/broken then turn on ur a/c system to make sure compresor works. If everything seems fine at this point and the system is "dry/hot" leave a/c on high and add 2 can's of freon and some dye to locate the leak, of course you will need the tool to add the freon (@ $10) and a leak detector kit (duno price, had it for a while). After this the a/c should be blowing cold air and u can now use an infered light to locate the leak. Its prob the condensor (located infront radiator) if so it will need to be changed (@ $120 for part). This is just the basics on how to check for leak, you can follow at your own risk! I went to school for mechanics and my bro is ASE certified so we did this at home.