Courtesy of Wachuku
IMPORTANT NOTE: What follows is for what I experienced on a '97 STS.
(1) Remove serpentine belt: 1/2-inch socket-wrench in tensioner pulley; pull hard towards front of vehicle; easily slide belt off power steering pulley.
(2) Loosen lug nuts on right front wheel (in preparation for access to compressor through right wheel-well).
(3) At a minimum put the right front on a jackstand (left front on stand probably good idea too).
(4) Remove right wheel.
(5) Remove frontward orientated access panels on right wheel-well, of which there are two. The first panel is held in place by five fasteners: three phillips screws along the outside running vertically, and then deeper in the well a 10 mm and 13 mm hex head. The second panel is partially beneath the first; it is held in place with three plastic pins. Use a pliers to pull the pin-heads straight out and the remainder will follow nicely.
(6) Remove A/C wire connector, on bottom-facing portion of compressor towards front of vehicle. (For re-connecting later note that the plug is self-polarized, allowing it to be connected in only on orientation).
(7) Loosen front compressor fasteners, totaling three -- a 15 mm nut to the left of the compressor (as seen looking in from wheel-well opening), and two more 15 mm bolts: one above compressor and one to its right.
(8) Now for the more difficult part: loosening rear compressor fasteners (end of compressor facing driver side).
(8a) Optional: remove oil filter. Removal can add some room. It can be done at any time if the need arises. I removed my oil filter, but whether it was necessary is debatable. I only lost about 2-4 oz of oil (honestly), but small drops of oil did drip on me occasionally from the oil filter housing, which was annoying.
(8b) Loosen, but do not remove, 15 mm bolt that affixes A/C lines to compressor. Using the A/C lines as a guide, the bolt fastening them to the rear of the compressor should be obvious. The bolt can be accessed with a regular 15 mm straight wrench (even with oil filter on). Best is probably to use the circular side the wrench, and to loosen the bolt just a little. There is little room to access the bolt; also, the plate the bolt compresses to hold the A/C lines in place, has a lip that makes getting a tool on the bolt-head difficult. Later, with the compressor partly moved from its regular position, the bolt can be better accessed with different tools for complete removal.
(8c) Detach rear plate that holds rear of compressor to vehicle. This requires a somewhat involved description. The rear of the compressor is affixed to a plate by two bolts, both either 10 or 7 mm, I can't remember. Both bolts are orientated along a driver-passenger axis parallel to the horizontal. One bolt near the bottom of the compressor is visible and easily accessible; relative to the first bolt, the other bolt is above and behind (towards rear of vehicle) and, depending on vantage point, may not be visible -- and I don't see how it would be accessible with a tool. However, the plate to which the rear of the compressor is affixed can be removed. The plate is held to the vehicle by a single 13 mm bolt at the bottom of the plate. The bolt is oriented along the vehicle's front-to-rear axis, parallel to the horizontal, with the bolt-head towards the front. The bolt is partially obscured from view, and for me, completely obscured from mechanical access by a flange on the plate. Nonetheless, the bolt can be easily removed using a "trick". First, the splash guard needs to be removed. It's a plastic piece on the bottom of the vehicle slightly in front of the compressor that spans almost the whole way across from driver to passenger side. Three bolts, 10 or 13 mm, I can't remember. With the splash guard removed, the 13 mm bolt holding the compressor back-pate can be accessed with a 13 mm socket and six-inch extender, which allows the socket-wrench to be accessed through the removed splash guard -- pending two other possible obstacles. It may be necessary to temporarily reposition a wire housing for a wire that goes to the oil pan. It may also be necessary to remove the passenger side radiator fan-assembly for access to the wrench. (If necessary, removal of fan-assembly is easy: two 10 mm bolts at the top; disconnect wire plug; follow wire with hand to disconnect wire housing attachment to fan; pull fan up and out, noting the bottom of the fan-assembly is held in place by a tab arrangement).
(8d) Fully remove A/C lines from compressor. With the plate still affixed to the back of the compressor, but detached from the vehicle, there is sufficient play in the A/C lines to shift the compressor around, predominantly towards the passenger side, which will ultimately be its exit direction (make sure front bolts are loose enough for this). Shift compressor to gain more room to access the loosened 15 mm bolt that the holds the A/C lines to the compressor. (If still not enough access, back plate can be removed, see (8e)). I found a 15 mm "chubby" wrench to work best. Longer wrenches bump into the car frame and don't allow much of a turn. The short chubby worked best for me for allowing significant partial turns on the bolt. Note that although more difficult, the bolt that holds the A/C lines can be completely removed without moving the A/C compressor from its usual working position, even with the oil filter in place (I did it).
(8e) With A/C lines removed and further "play" available for compressor, the back-plate can be removed if necessary, or if possible this can be done with the compressor fully removed.
(9) Remove compressor through opening from removed access panels.
Installation of new compressor is reverse of install, with a few important notes. While there is still plenty of play with the compressor position, I would recommend getting a good start on tightening the bolt that holds to A/C lines to the compressor. Final tightening can be completed when the compressor is fully affixed in place, like the initial loosening in step (8b). Also, note that there are two washer-shaped gaskets associated with the two A/C lines connecting to the compressor. Be mindful that these gaskets do not come out of place. If they do come out of position, re-position them with flat-head screwdriver or similar tool. Be sure to check the gaskets before any hard tightening of the bolt that affixes A/C lines to compressor. Note also that the gaskets should have some refrigerant oil on them.
The accumulator should be replaced whenever compressor is. The accumulator is sensitive to moisture and should be replaced last, right before new refrigerant is infused. The accumulator is next to coolant surge tank. Use two crescent wrenches to detach A/C lines: one wrench to hold line, the other to turn junction interface.
Orifice tube should be cleaned at a minimum, replaced if possible. It is inside A/C line near fire wall, at A/C line junction slightly towards passenger side (preceding evaporator inside vehicle). It is in the line towards the passenger side, look deep. Also be mindful of orifice tube orientation (which I believe is short side towards evaporator). Below is a link to a thread with a few more detsails about the orifice tube:
http://www.cadillacforums.com/forums...fice-tube.html (orifice tube)
See posts above for info about whether to flush A/C on not. In my case -- small, slow refrigerant leak through compressor -- neither dealer nor independent mechanic recommended A/C flush.