The Mysteries of Porsche 911 Auto Heat
(For Manual Heating - See Notes at Bottom)
Major Heating & Ventilation
Components of a 1987 911
Earlier & Later Models Have Similar or
Equivalent Components
(AC Components Not Shown for Simplicity)
Now you can begin to appreciate the madness of Herr Docktor Porsche.
Hahahahaha.
Main Heater Blower Fan
Sucks hot air through the main engine fan & shroud & sends it to the heat exchangers to warm up. If the main blower fails, the system fails, because the main relay needs to see a load from the blower motor.
Fuses & Relays - Engine Compartment
Fuses for main blower & relay. This is also where the main blower relay is located. This is a crucial link to many mysterious problems - hint: footwells.
Heat Exchanger Duct & Valve (see Close Up)
This valve open & closes to allow heated air into the rocker panel ducting. A servo in the Automatic Heating Control pushes the lever which pulls a cable which pulls a cable that opens the valve. Get it?
Heat Exchanger Temperature Sensor (see Close Up)
Thermostatic sensor for the Automatic Heating Control. The Bentley says it turns on when it senses heat. Many report a permanent On for this, but?
Automatic Heating Control
This controls the opening of the heat valve & the fan speed of the footwell blowers - 10 speed switch (0 - 9)
Heat & Fresh Air Controls
This controls the fresh air fan & fan speed as well as the blend of air sent to the windshield area (defrost) & the dash vents & footwell area. The slide controls for blending, open or close various duct valves in the trunk & footwell areas.
Automatic Heat Sensor
Thermostat control sensor for Auto Heat. Really stupid in a top down Cab, btw. Rumor has it that this even has its own intake fan. On older models it was between the sun visors.
Footwell Blowers
Auxiliary blowers (one on each side behind a carpeted kick panel) to give the heated airflow a boost.
Footwell Series Resistor
Like its name, a big series resistor mounted on the trunk firewall that allows 3 speed operation of the footwell blowers.
Fresh Air Blower
Sucks in fresh air & road kill particles from the grill in front of the windshield.
Fuses & Relays - Trunk
Fuses & relays for the footwell blowers. Note: Footwell blowers also had an inline fuse from mid-87 & many earlier cars may be retrofitted with them.
Manual heating includes all of the same components with only a few exceptions:
1. No Automatic Heat Sensor
2. The Automatic Heating Control console instead houses a 4 Speed switch (0-1-2-3) that controls the footwell fans.
3. 2 red paddles straddle the E-brake. These turn on the main blower via micro switches & each pulls a cable to open the Heat Exchanger Valves on their respective sides.
4. Lighted indicator beside the red paddles to indicate the Defrost function of the paddles. Not all cars however.
Red paddles & Footwell Speed Controller
(manual heat only)Lighted Defrost Indicator
(Not all cars)Photos courtesy of Rennlister Luus
