Discharging my AC compressor.

2002 LS V8 3.9 240k miles.

Replacing my AC compressor this weekend. I believe there is little to no freon left in the system because the air blows lukewarm, and there is a long hiss under the dash when the compressor clutch kicks in.

Is it necessary to take it somewhere to have the system discharged, or is it safe to assume there is nothing left in it to discharge? If the latter, how and where do I open the system to let it discharge before I start removing the compressor?

Thanks

Does the compressor clutch still engage when you turn on the A/C? If so, there is still quite a bit of R-134a in the system. Even if the clutch does not engage, there could very well be quite a bit of gas in the system. Actually, you'd better hope there is, because if the leak is so large that all the gas leaked out, you will have moisture contamination in the system that may be expensive to fix. Since the refrigerant gas is what carries the oil to lubricate the system, pressure switches will prevent the clutch from engaging if the pressure is too high or too low which means just because the cooling is ineffective, that's not a good sign that little to no R-134a remains. I won't bother to speak to the legalities of knowingly venting your system to the atmosphere, which would be enough of a reason for no one to post here recommending you just open the system up without the proper recovery equipment.

Typically a shop that does A/C repair is pretty happy to evacuate the A/C system for you for a relatively small charge. They can recycle the gas and sell it to someone else. Some shops will even give you a credit on what they pull from your car that you can apply to having them recharge your system after the repairs are made.

Since you're asking where to open the system, I'm guessing you probably don't have the vacuum pump to properly evacuate and perform a gross leak check on the system once you replace the compressor. If you have a shop picked out to help you recharge the system, they should also be able to capture what's left in the system before you start as well.

-Rod

Yes, the clutch still engages. I just stopped using it because it's cool enough here to not really need it. Based on your comments, I have to assume that there is a significant amount of gas left. Therefore I will take your advice and have it drained. Thanks Rod.

I got the compressor replacement done and I hope I never have to do it again! ...I say that every time I work on this car. There is an accurate utube video.. https://www.youtube.com/watch?v=Jplhqj78q24&t=725s
..on this job but beware, that top fastener bolt tha'ts hard to get to, does not break free as easy as it does in the video, and the compressor does not drop out as easy either.

Fast Forward to after the system got recharged. On the way home everything seemed normal. The AC system was operational again. But when I got home and turned the car off, there was this humming coming from under the hood, like a sub motor was running. and I could hear and feel the vibration of fluid moving through the AC lines. The humming lasted about 5 minutes and stopped. Since then the AC has been working fine.

But I have to know Rod, what was that humming?

Since it sounds like you had the hood open to notice the flow through the lines, I assume you would have also noticed if the radiator cooling fan was still running. Could it have maybe been the auxiliary coolant pump?

-Rod

Petty sure the fans were not running. It was a very low sounding buzzing. ...like the system was re setting the new ac hardware and coolant.

Hmmm, not sure what that might have been then. Maybe the DATC was modulating the DCCV? If it happens again you might try disconnecting the DCCV to see if the noise goes away then.

-Rod