October 2020

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OCTOBER 2020 WWW.PNWR.ORG 17 way to check proper flap position is by removing the output hose and looking in the end of the blower outlet opening to see the position of the flap. With the control lever in the left hand "off" position, the flaps should be closed and in the right hand full "on" position, the flaps should be open. If this valve does not close properly, the actuating cable needs to be adjusted so that it will allow the warm air to get into the delivery ducts without being diluted. Adjustment can be made by loosening the adjustment screw, moving the flap to the correct position and re-tightening the screw. 3. Auxiliary Blower System Checks (1984-1989): Things get a little more complicated for the 1984-1989 cars with manual heater controls because of the added auxiliary blowers in the side ducts (Figure 3). However, the system still has to be first checked to make sure the heat control valves are adjusted properly so heat can get out of the heat exchangers and secondly, the heater blower has to be checked to make sure it will run properly. Even with the manual heater control system, the small control console behind the gear shift lever contains the switching functions for the auxiliary blowers. The electric blower mounted on the engine is still the primary warm air mover and the auxiliary blowers do not receive power until the electric heater fan in the engine compartment is running. An electronic control unit is added in the engine compart- ment instead of the earlier relay and power to run the engine electric blower is still taken from the engine compartment fuse panel. Once the blower is started, power is then made available to allow switching on the front auxiliary blowers. The front blowers use a relay mounted in the front trunk fuse panel and it receives power from the no. 3 fuse block (most aft 3 fuses) in the front fuse panel to run the auxiliary blowers. A wiring diagram for the 1984 911 heating system is available in Reference 1. It should be noted that the automatic system electronics were changed in the 1986 911 Carrera models, so owners should check the wiring diagram for Figure 3. 911 Carrera Auxiliary Heater Blowers. their specific model year. Electrical problems can develop in both the aft and forward portions of the system, so a systematic check from the fuse to the relay and its output need to be done starting in the engine compartment in case the electric heater blower at the engine is not working. A new rear heating controller may be needed to get the electric blower going. If the engine electric blower is working, but not the forward auxiliary blowers, then continuity with the forward relay, and its output power can be traced to determine where a forward blower problem might be. 4. Pre 1989 Automatic Heating Systems: The automatically controlled heating systems have very similar functions to the equivalent manual system except for the added thermostats and automatically operated heat controls. The automatic operation of the heat control valves is accomplished with a small mechanized lever that continuously pushes and pulls on the control cables to the rear heat control valves from the control console in response to temperature variations. Sometimes failures can occur due to the mechanical connectors between the actuation rod and the cables. In some of the earliest automatic systems, an exposed manual lever was retained and after an adjustment could be used in case of failure of the automatic actuator to operate the valves. The later automatic systems eliminated the manual lever. References 1. A. Caldwell, "Early 900 Heating Systems," Panorama, February, 2001. 2. 911S, Carrera, Service Information, Model 75, PCNA WKD 454 121. 3. 911 Carrera and Turbo Service Information, Model 84, PCNA WKD 490 221, 7/83. 4. 911 Carrera 4 Service Information, 1989 Model 964, PCNA WKD 495 121, 12/88. 5. 911 Carrera (Model 993) Service Information, PCNA WKD 498 621, 7/93. 6. A. Caldwell, "911/912/914 Ventilation Systems," Up-Fixin der Porsche,

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