If you discouple the coupler, yes, refrigerant will spray everywhere. That can spray in and damage your eyes, freeze your skin etc. Plus there's oil in the mix that will cover everything near where you are working.

The correct way to kill the rear A/C is to either close off the hard tubing heading rearward OR replace that plumbing with the kind meant for front A/C only.

If you were to do one of the above, the job would require safely and legally evacuating your A/C system of refrigerant (illegal to vent it to the atmosphere, must be evacuated at a licensed A/C place). Then you'd be essentially rebuilding and recharging your A/C including new accumulator, orifice tube, O rings, refrigerant, oil etc. Then recharge the thing with the appropriate refrigerant.

Pretty big, involved, expensive job for very little return. If the system isn't leaking, it's probably simpler to leave it in place. Turning it on from time to time is probably good practice to keep the refrigerant circulating in the rear half.

The rear A/C in my 89 is intact but hasn't been used in years. I have rebuilt the front half and converted from R12 to R134a. It's not as cold as R12.

Lump

 

I gutted my passenger van to use for work, then as a camper van, so I've removed the rear air. My ac was not working at the time so I didn't have any refrigerant in the lines.

The rear air has an evaporator that runs in parallel with the regular front evaporator; all other parts are common to front and rear, accumulator, compressor, condenser. I got front air only parts from the junkyard to convert: the low pressure hose and manifold that runs from accumulator to compressor, and the high pressure line that connects condenser out to front evaporator. Other people have written about cutting the lines and plugging them with compression fittings.
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While the system is open you should replace the accumulator and orifice tube, and might as well replace all the o-rings with new; all those parts will be $25-$35. I needed a new compressor as well. Reassemble, vacuum the system, then recharge.

Besides the rear evaporator and blower unit inside the van this is all the tubing that I took out:

Here is the whole thread from my experience. It's an old thread and some of the old pictures show up as red Xs, just click on the X to see the attachments.
viewtopic.php?f=34&t=8008

 

Ok, so should you return....does it not work now? Mine works..and it cools the van on 100 degree days down to 72 with no issues. Front AC only..for the rear..if you live in hot climates..is not so good.

 

Thanks for the warning guys. I think it'll be fine to just leave it installed and panel over it with new interior I am putting in. More work than it's worth to have it gone.

 

I removed mine and thought it was totally worth it - it takes up quite a bit of space.... I took it to my local A/C shop and had it discharged, then they cut the two lines and welded them shut - one down low where it branches out from the condenser, and the other where it branches behind the compressor, then recharged the system... My front A/C works great, and removing the rear was just a matter of unbolting and pulling.... I can't remember what they charged, but it wasn't a deadly amount.... took an afternoon to do it all....

Just depends on how much you'll wish it were gone later when you do your build out....