electrical wiring help-relay

rfuerst911sc · 01-16-2005, 01:27 PM

Hello today I continued my AC upgrades and tried to wire the fan on the aux. condensor I mounted in the left rear fender.I purchased a 4 pin 30amp relay-it has pins # 85,86,87 and 30.It appears that pin 87 and 30 are on the switching side and 85 and 86 go straight thru the relay.What I was trying to accomplish is to run a wire from the wire that activates the compressor to the relay,I thought this would be the trigger wire.I then ran 12v power to the other pins,no matter what combo I tried I couldn't get the fan to run.When I connect a ground wire and 12v power to the fan it runs great but I can't figure out this damn relay...........help please!!!!!!!!!

Early_S_Man · 01-16-2005, 01:36 PM

Testing Relays

autobonrun · autobonrun's Garage

I'm not sure what type relay you purchased. On Porsche relays, pins 85 and 86 are to the coil. Pins 87 and 30 are normally open contacts for the switch portion of the relay.

Try connecting pin 85 to a ground point. The 12v signal to activate your relay would connect to pin 86. This may be from your A/C switch.

Then the power supply for the fan would be switched using pins 87 and 30. Run the 12v supply to pin 87 and a wire from pin 30 to the fan. Then connect a ground wire to the other side of the fan.

Assuming the contacts on the relay are normally open, when the relay picks up, the contacts will close suppling the 12v to the fan.
Alternately, you can switch the ground leg, but I like switching the hot so that when the fan is not running, there is no voltage at the fan itself.

rfuerst911sc · 01-16-2005, 02:00 PM

Thanks for the quick replies guys.Autobonrun I think you explained the only combination I didn't try,I will try that combo tomorrow.The relay I purchased is a Discount Auto generic relay but should be fine for this application.Electrical is my weak point,I really appreciate the feedback.

rfuerst911sc · 01-18-2005, 02:48 PM

Autobonrun you are the man!! I wired up the relay today as you described and it worked perfect,thank you for the help.Now my AC upgrade can continue.

autobonrun · autobonrun's Garage

Glad I could help. Electrical circuits can be very frustrating. It's always a relief when you get them to work. If you want to read more on circuits, I posted a link a while back on basic electric circuits. It is by far the best free on line source for information on all types of electrical circuits that I've seen.

911pcars · 01-18-2005, 07:38 PM

Autobonron wrote:
"On Porsche relays, pins 85 and 86 are to the coil. Pins 87 and 30 are normally open contacts for the switch portion of the relay.

Try connecting pin 85 to a ground point. The 12v signal to activate your relay would connect to pin 86. This may be from your A/C switch.

Then the power supply for the fan would be switched using pins 87 and 30. Run the 12v supply to pin 87 and a wire from pin 30 to the fan. Then connect a ground wire to the other side of the fan."

Everyone should keep Autobonron's description for future reference. One good thing about DIN-spec components is that they're consistent across the board, so all Bosch-equiv. relays use this designation.

In automotive vernacular, this is a normally open (NO), one make relay. 85 and 86 is the control circuit; the circuit that energizes the electromagnet and causes the switch to close inside the relay.

87 and 30 is the power circuit. One of the two (e.g. 87) connects to source voltage (battery/fuse); the other (30) connects to the load (e.g. fan motor, bulb, etc.).

Sherwood