The air conditioning system in the SL-C has had several iterations throughout the years. The current version is from Vintage Air, and uses a semi-custom case based on their small AC system series. The current system has both heat and air, and has conventional controls (i.e., non-electronic).
The car kit comes with the AC system packaged from Vintage Air, an AC compressor bracket for LS engines, a large fiberglass duct for air distribution, a heater control valve (more about that later), and two dash vents.
There is a good discussion in Ken R's thread here including pics of the compressor, ducting, etc.
Mounting the AC Compressor
If you have an LS engine, the kit comes with a compressor bracket from Superlite. This is a decent basic bracket. There is a good discussion, with pictures, at this link.
Ken R came up with these two other options: first is the Dirty Dingo mount available here. Several builders have it and like it. Also, Holley has recently come out with a great bracket for a low-mount compressor- check it out here. Both solutions require the Sanden SD7 or compatible compressor, which has been shipped in the AC kits- but check yours to be sure before you order a bracket.
For other engines, you are on your own- there are just too many variations, even within a common engine family for the factory to come up with a solution for every possible engine combination, and the LS engines represent about 90% of all engines used in the SL-C, so almost all builders will be covered by the factory bracket.
The Vintage Air kit comes with a heater valve that unfortunately doesn't work optimally with the LS engines.
Unlike the old small block Chevys, the LS engines need to have the heater circuit on the engine always open. The solution is to use a 4-port valve that always recirculates coolant back to the engine regardless of whether the heater is on. There are two types of these valves available that will do the trick.
The first solution is a manual valve that uses a cable to open and close the valve. You can use Delco part 15-5533, which is from a 95-00 Chevy pickup. This is inexpensive, but uses a cable, instead of an electronic control. You'll need to provide a cable- the part doesn't include one. You'll also need hose size adapters as the barbs on this are the same size- the LS engine uses a 5/8" and a 3/4" barb.
Another solution is essentially the same valve, but with electronics replacing the cable. With this valve, a knob on a potentiometer controls the amount the valve is open. You don't need hose adapters- this valve already comes with the correct size barbs. A further benefit is that the control is electronic, allowing easy location of the knob just by extending wires. Also, since the wires are to a potentiometer instead of directly controlling a power-hungry motor, the wires are smaller, and safer, as they carry much less current.
If you live in a hot desert and don't need heat, don't cap off the two heater outlets on the LS engine. You should instead run a small hose that loops from one barb to the other. Note that one barb is 5/8" and the other is 3/4", so you'll need a hose that makes that transition. These can be obtained from NAPA or other parts stores (need someone to get the part number)
Compatibility with Electronic Controls
A common question is whether the stock AC system can be controlled by the Infinitybox INvironment controller, or other similar electronic controllers. Sadly, the answer is no. Only the Vintage Air GenIV systems can be so controlled.
Several builders have tried to fit the GenIV evaporator in the interior of the SL-C without success. If you are the first, please show the rest of us how you did it!
However, the fan motor in the current evaporator can be electronically controlled using an inexpensive motor controller, as from eBay. Here is a link to one of many such controllers that can do the job. The author has a similar unit on his SL-C and it works well, allowing a smooth, non-stepped control of the fan speed.
Controlling The Compressor
Most compressors are rated for a max speed. Exceeding that shortens their life, sometimes Right Now. See this discussion about how to manage that.
Most SLC builders enjoy cool air after an install. But there are common problems that it helps to know about, so you can avoid them in your build. Here are a few of them:
If your car has better cooling when cold, and noticeably less when hot, you may be getting heat soak in the condenser. Be sure to leave at least an inch between the radiator and the AC condenser to avoid this. It's a common misconception that it is fine to butt the AC condenser up to the radiator- don't do that to your car!
Another possible cause of heat soak is internal to the evaporator. The lightweight, simple design of the evaporator encloses both the heater core and the AC core in the same box, with no separation. Since there is no way to prevent running both the heat and the AC at the same time, having even the slightest amount of leakage through the heater control valve will have a noticeable effect on the temperature of the cooled air if the AC is on. That's why it's key to ensure that no coolant is flowing through the evaporator when the AC is on. If you can feel heat in the hoses leading to the evaporator, that heat is making the AC coil much less effective. Of course, allowing the heat and AC to run at the same time allows you to manually blend the two, making it possible to de-humidify the air, as well as heat it during cold periods. Just be sure the heater control valve is completely closed and that no coolant is leaking past it and into the evaporator when you are trying for max AC.
This probably should have been the first topic under problems! AC systems do not tolerate leaks, and they must be pulled down with a vacuum before charging to be sure there are no leaks. Steadily declining AC performance over time is a sure sign of leaks in the system. These can range from loose connectors, all the way to missing o-rings (you did put the right o-ring on every fitting, right?). There are various methods for detecting leaks that are well-covered on YouTube.
Another source of leaks is not in the high-pressure AC system, but more insidiously in the duct system from the evaporator to the outlets. It's common to have sealing problems from improper application or just old sealants that seal the manifold to the chassis, or at hose connections, especially at the vents. Check these carefully before jumping into the high-pressure lines so you can rule out the easy stuff first.
As is documented elsewhere in the wiki, excessive RPM can blow the seals in the factory compressor. The compressor in the kit is a standard Sanden-style compressor as used in many applications worldwide, and known to be a reliable compressor. But it is only rated for around 6K RPM- and when installed with pullies that are commonly used, the compressor typically spins at higher than the engine RPM on your tach. The prevention is described above (in Controlling the compressor) but if you have a total AC failure and you know the clutch is engaging but still have no pressure, the compressor is likely shot.
You should hear the clutch on the compressor engage when you turn the AC on, especially with the engine off. If the clutch isn't engaging, the compressor won't work and you will be hot and miserable. Typical causes for this are improper wiring, or a faulty pressure (e.g., trinary) switch.
Improper system pressure
It's possible to improperly commission the system with either too much or tool little refrigerant. The idea that "if a little is good, more is better" doesn't apply to measuring refrigerant in the system. The proper amount is determined by looking at pressures under different circumstances. If you aren't sure, consult an auto AC shop for help in getting the correct amount of refrigerant into your system.