1978 – 1979 Porsche 928 A/C Compressor Relay No Longer Available

This relay is no longer available and used relays are difficult to impossible to locate. 

This Air Conditioning Compressor Relay P/N 928.618.105.00 provides two special functions.  It will not turn the A/C compressor on until the engine is started and also provides high-RPM cut-off protection. 

 

The connections to the Speed Relay, AC P/N 928.618.105.00 are: 
30 = output voltage from Temperature Switch Evaporator
31 = ground
31b = engine RPM signal
87 = switched output, circuit to Air Conditioning Compressor Clutch 

 

This relay is no longer available and used parts are difficult to impossible to locate.  If your relay fails, first remove it and clean all the pins and spray a contact cleaner into the relay socket.  After 45 or more years the contacts become tarnished and corroded.  This may be the “simple” fix.  If the relay still doesn’t function, an electronic repair shop may be able to refurbish it.  Cleaning the contact points with an ultra fine grit sand paper may correct the problem.  If the electrical components in the relay fail there are commercially available replacement transistors, capacitors and the 8-pin DIP NE555P IC OSC SINGLE TIMER 100KHZ IC.