My A/C would shut off when the outside temperature was above 98 deg F. At that time, I had power at the connector to the compressor. In the 1999 model year, Volvo changed to a different type of A/C compressor, that does not have a superheat switch, which explains why I couldn't find it. My system did have a black box bolted to the side of it that some people said was just a diode, and an A/C tech said was a type of superheat switch. I also noticed that my fans did not always run when the A/C was on.

I decided to have the dealer check for computer fault codes before going further. The tech said that there were no fault codes, but that he would check for voltage drop across the connector. He did so, and replaced the connector. $120 later, I had the car back, but it turned out that the A/C was not fixed. I decided to wire around the black box and the connector through a diode to eliminate all the possible problems between known power and the clutch. Two days later, the clutch stopped working entirely. I do not know if the black box contained some kind of resistors that lowered the voltage, and putting 12V directly to the clutch burned it out. (I doubt it.)

At any rate, I bought a new clutch from Brentwood Volvo for $199, and installed it. It was 105 - 100 deg F today and the A/C is working fine. The new clutch is redesigned, and no longer comes with the black box diode/superheat switch.

It IS possible to replace the compressor clutch without discharging the A/C and removing the compressor, but it is not a job for the faint of heart or someone who is not experienced. Follow the directions that you get from www.alldatadiy.com, but do the following things differently:
1. Don't discharge the A/C system.
2. Remove the bolt holding the receiver dryer bracket to the car, but don't disconnect the receiver/dryer.
3. The manual tells you to remove the 2 radiator bolts and swing the radiator forward. This looks like a bad idea to me. If you do that, nothing is holding in the radiator but the hoses. I removed the right hand bolt and loosened the left hand bolt, so that the right side could swing forward.
4. Unbolt the compressor and move it to where you can access the center bolt on the clutch plate. Remove the bolt. You probably need an air impact wrench to get it off, unless you can stop the plate from turning when you try to unbolt the bolt. (Don't overtorque it going back in. The spec is 10 ft/lbs.)
5. The manual tells you to pull off the clutch plate. It will not come off. What they don't tell you is that there are 3 5MM holes in the plate. You need to get three 5MM bolts, about 1 1/2" long, and thread them into the holes. Tighten them evenly, and it will pull the plate off. If you don't do it evenly, the plate will get cocked and stop coming off.
6. Using a six inch wide, 2 jaw puller, remove the pulley. You have to rig something up to protect the end of the compressor shaft. If you damage this shaft, you will be buying a new compressor.
7. Using an impact screwdriver, remove the 3 screws holding the clutch coil to the compressor.
8. When reassembling, don't forget to put in the clutch plate spacer shim(s). The new clutch comes with 3. I used the one shim that was in the old clutch. (It was stuck inside the clutch plate, so you have to go look for it.)

Re-assembly is the reverse of dis-assembly.

This job took me 5 1/2 hours. It requires a lot of patience and working in a very tight space. Flat rate for a compressor clutch is 2 1/2 hours, not counting discharge/recharge. If you are paying someone else to do the job, you may end up paying less by having them discharge the A/C and do the clutch on the workbench.