06-02-2007, 11:50 AM
Join Date: Jul 2006
Total Cats: 71
2 stage fan mod
Goal: Have first fan stage circuit excite at 175 F. Have second stage fan circuit excite at 206 F. Do not interfere with A/C control over pass side fan.
engine temp < 175 F = No fan
engine temp > 175 F & < 206 F = Single stage fan
engine temp > 206 = 2 stage fan (both fans running)
A/C on = A/C fan on, regardless of engine temp
Required items: SPDT relay, primary wire, crimp connectors, electrical tape, 30A fusible link
Instructions: The relay has 5 positions, wire as follows
Pin 30 to A/C side fan black/blue stripe wire FAN SIDE OF WIRE
Pin 85 to thermosensor
Pin 86 to +12V
Pin 87 NO to +12V (high power)
Pin 87a NC to A/C side fan black/blue wire on the CAR SIDE OF WIRE
You need a real automotive SPDT relay with a true NO contact and a true NC contact. The el cheapo $1.49 relays probably won't cut it. It should run $7-10.
You can grab +12V at the underhood fuse box. There are a variety of places. I had an unused position, so I crimped a spade connector onto a 14ga wire, and inserted it into the bottom side of the unused positon. Then reinstall the fuse block and insert a 30A fusible link. *(I ran this wire to both pin 87 (high power input) and pin 86 (switched 12V) so that my relay had power full time. If you wanted the relay to only work key on, you would need to run a switched on +12V source to pin 86.)
The A/C side fan has 2 wires. Leave the black wire alone. Cut the black/blue stripe wire. The side of the wire that goes to the fan connects to pin 30 on the relay. The side of the black/blue wire that comes from the car goes to pin 87a on the relay.
The thermosensor on top of the thermostat housing has only one wire. Cut it and bring it to pin 85 on the relay.
Tape everything up and make sure all your wiring is secured.
Last edited by Ben; 06-03-2007 at 02:54 PM.