I'm in the middle of fixing the AC on my 99 GS300. I couldn't find too many posts about AC work, so in case someone else is planning this type of job, here's what I've learned so far. I'm not going to post all the details about the job, just the things I wish I'd have known. Read the last one for why I'm back inside rather than finishing the job.

A. Removing the compressor:

You have to have an E-10 external torx socket. Go ahead and buy one - the stud-bolt on the rear of the compressor has to be removed to get the thing out.

You don't have to remove the radiator, but you do have to remove the fan assembly. That's the only way I had room to get the compressor out. I only spilled about a pint of coolant when I disconnected the top radiator hose to get the fans out rather than the gallon I would have spilled removing the whole radiator.

There's 5 bolts that hold the GS300 compressor on (Someone on here posted about 3 bolts - that's for the GS400). Before you loosen those bolts, you also have to loosen the bracket that sits behind the Power Steering pump pulley (you can get to 2 of the bolt heads through the pulley - the third is shared with one of the compressor bolts.

B. The expansion valve:
The service manual says to remove the entire dash to change the expansion valve. I thought I knew better. I took the kick plate off the underside of the instrument panel, and could see the expansion valve sitting above the brake pedal with its 2 screws and was lulled into a false sense of ease. I was able to get the old one out and get the new one in with new o-rings, but it took a lot of prying and I caused a little bit of damage to one of the o-ring grooves. We'll see if it seals when I pull a vacuum on it later. I saved a lot of time (1 hr vs 4 or more), but if it doesn't seal, it's back to square one.

C. The Dryer Desiccant (my biggest mistake):
The desiccant bag sits in a tube on the passenger's side of the condenser. I removed the condenser and removed the old desiccant to flush the condenser before reassembling with the new filter and desiccant. Be VERY CAREFUL when working with the plug on the bottom of the desiccant tube. I temporarily reinstalled it for the flush, and COULDN'T GET IT BACK OUT. the soft aluminum plug galled in the tube and my 10mm allen key rounded out the plug. Now I've got to wait for the parts store to order a new $160 condenser and leave the car partially disassembled for a few more days.

If you replace the Desiccant (as you should when you open the system), there's a reason they give you a new plug in the kit. Don't re-use the old one, and put PLENTY of PAG oil on the threads when you install the new plug. I'm kicking myself for replacing a perfectly good part because I was an idiot.

 

Honestly, you almost never have to replace the desiccant bag. As long as the car has never had the system exposed to the elements for long periods, then you are ok. Like having the system pulled apart for a day or two then putting it all back is fine. Hell, I have put condensers back in after sitting out for months and they still work no problem with the same desiccant pack in there lol. However I really recommend doing it if you had a compressor seize and the metal shavings get all through the system.

 

Yep. That's exactly what had happened to me. The little screen cartridge below the desiccant bag had all kinds of shiny things stuck to it. Compressor hadn't seized, but it was worn out (couldn't get enough pressure differential).

The only thing I'll add to this is to be careful when replacing the condenser. The mounting hardware in my aftermarket condenser (I know, should have used DENSO, but the local guy didn't have it) was longer than the original and came awfully close to the refrigerant lines in the condenser. It would be an easy way to ruin a condenser by over-tightening the mounting hardware (I just re-used the old, shorter screws and they worked fine with plenty of clearance.

Now the AC is fixed (no leaks, held vacuum for an hour) and I have a happy wife. I saved a lot of money, but paid for it in aggravation. Lesson learned.

 

I pulled my AC compressor out without having to remove anything else except the under carriage protector. I jacked up the car, remove the under guard, and the bolts for the AC were exposed. I used a universal to maneuver around the other parts. I have a 99 GS3 too.