Issue link: http://digital.nexsitepublishing.com/i/1404782
29 Spiel – August 2021 to the starter solenoid circuit 50 which is hot when the starter is engaged. There is also a small resistor built into the relay (not shown in the factory wiring diagram, but indicated on the outside of the relay case and added in Figure 2) that jumps across between the black and yellow wires. It appears that when the starter is engaged, the relay coil has 12 volts on both ends (black and yellow wires), and the relay remains open with no output power getting through. When the starter is not engaged, there is 12-volt power from the black wire that energizes the coil and grounds through the solenoid. The energized coil keeps the relay closed and power available to the air conditioner. The original relay (911.615.103.00) was superseded in 1988 with a slightly different design (911.615.103.01) that has an external 16 amp fuse and no internal resistor. The whole purpose of the relay is to prevent the air conditioner from drawing any power during engine start (i.e. in case the owner didn't turn off the air conditioner when he last parked the car). In other words, it has nothing to do with the normal operation of the air conditioner except to keep the AC from running while the engine starter is operating! But it can provide a possible source of failure. Notice where the relay is located. It is fastened to a stud on the right- hand wall of the luggage compartment that also just happens to be the inside wall of the right-hand front fender well. This location is about two to three inches below two environmental hazards: (1) the two 200°F+ engine oil lines that carry oil to the right front fender oil cooler and (2) the vent louvers to the outside fender area that allow water and dirt into the compartment. It is not the best environment, and I found evidence of some water damage on the relay in my 911SC that had never been changed since the car was new. Apparently, the relay suffered from intermittent heat effects since bypassing it that allowed the air conditioner to work afterwards without any stoppages. Relocation of the relay away from that wall is a major improvement and is easy to do. The conclusion to this story is that, if the relay fails, the air conditioner can be easily restored to normal service by bypassing the relay altogether and connecting the red and white wire from the main S-20 fuse directly to the red wire going to the rest of the Figure 1. 911 Air conditioner schematic