Because the York compressors cause engine roughness at idle and have a tendency to leak, I decided to upgrade to a more modern design. I obtained a new Seiko-Seiki rotary vane compressor, mounting bracket adapter, hoses, and belt. (Figure 1) This is a true rotary unit, similar to a Wankel engine. (Figure 2) Here are the steps in replacing the factory compressor.
Take the car to a shop with the proper equipment to recover the refrigerant, and have the system drained. Now you are ready to remove the old compressor.
Loosen the three compressor mounting bolts (6mm allen-head or 13mm hex-head), and back off the 13mm adjustment nut. Remove the three compressor mounting bolts, and remove the compressor belt.
Remove the top (discharge) hose from the compressor, and from the engine lid condenser. Be sure to counter-hold the fitting on the condenser with another wrench-this is a fragile and expensive part. (Figure 3) Tip the compressor up on end to gain access to the suction hose, and unfasten it from the compressor. This hose will be reused, so there is no need to detach its other end. Remove the old compressor, and check that the bolts holding the compressor mount to the engine are tight. Remove the mounting adapter plate from the old compressor, and attach it to the new compressor.
Before installing any hoses, lubricate the hose fittings with refrigerant oil or motor oil. Connect the new suction hose extension to the old suction hose. (Figure 4) As you install and tighten the hoses, allow them to assume their natural position, so they are not twisted. Make sure the hoses don't rub against anything sharp, or have any sharp bends. Route the hoses so they don't interfere with removal of the oil filter.
Place the new compressor on the engine, tilt it toward the center, and install the new belt. Now you can install the three compressor mounting bolts, but don't tighten them yet. Connect the suction hose to the compressor, and install the new discharge line between the compressor and the engine lid evaporator. Adjust the compressor belt, and tighten the compressor mounting bolts.
The next part of this job is to replace the receiver-dryer. The receiver-dryer acts as a filter to remove water and contaminants from the air conditioning system, and should be replaced any time major work is done on the system. It is located in the left front wheel well, behind the wheel. (Figure 5) It is a good idea to clean this area, especially around the hose fittings, before proceeding. This is a dirty location, and the air conditioning system won't tolerate dirt. Loosen the two hoses at the top of the receiver-dryer, unfasten the hose clamps holding it in place, and remove it. It is easier to completely remove the hose clamps for this part of the job. Install the new receiver-dryer, tighten the hoses, and reinstall the clamps.
Now you are ready to go back to the shop, have the system vacuumed down, and the refrigerant reinstalled.
The Seiko rotary vane compressor is much smaller than the old York. (Figure 6) It is so quiet and smooth I can't tell when it cycles on and off. You can even change spark plugs without moving the compressor (and maybe even adjust the intake valves).
The last step in this procedure is to enjoy cool summertime driving in your Porsche. The air outlet temperature in my 911 is now lower than in my wife' s brand new car!