funny electrical problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

HvyChevy454 · 10-20-2002, 11:01 PM

ever since my father and installed eletric fans, whenever i go to turn the truck off i can turn it off take the key and be ou tthe door before it will kill the motor. If i un hook the fans it shuts off immediately?

Longhorn Man · 10-20-2002, 11:11 PM

The fans are turning after the power is shut off, and they produce enough of a charge to fire the coil. THey act as a small generater.
You need some kind of a diode (think of it as a one way check valve for electricity) that will stop the problem.
It is a common thing when installing electric fans.

Hooter · 10-21-2002, 12:59 AM

ya what longhornmail said, Go to radioshack and ask them for a big mofo of a diode one that can handle a few amps of juice

BobbyK · 10-21-2002, 07:25 AM

IF you run relays with your fan you wouldn't have that problem.As soon as the key is turned off the cicuit to the fan is interupted so it doesn't feed back into the system.
you can see the ones I used in the bottom left corner of the fan shroud,One for each fan.

Lippyp · 10-21-2002, 09:43 AM

Definitely make sure your fan is wired through a relay. I have a single fan on my truck fitted by the previous owner and it wasn't wired via a relay. It was switched by an illuminated switch on the dash which would light up even when the fan was off as the fan windmilling in the ram air as you moved generated enough power to light the bulb. I also found when stuck in traffic one hot day that the connections at the back of the switch were too hot to touch, so could easily have caused a fire. Fitted a relay and a new fused supply from the battery and all is now fine. For the sake of a couple of dollars you could lose your truck to an electrical fire, sort it out now!

6869704X4 · 10-21-2002, 09:53 PM

A quick fix is to change your power source. Sounds like you got it wired through the ignition.

BobbyK · 10-23-2002, 02:00 PM

I run my fans direct from the battery with two 30 amp ciruit breakers(one for each fan).
On startup the fans can requiere a good deal of amps to start turning(depending on fan of course).The circuit breakers are self resetting so there is no need to change any fuses.
Wiring high amp peripherals such as electric fans without relays and fuses or breakers is not recommended.A run-of-the-mill toggle switch is just not designed to handle the full amp draw of an electric fan.Use that toggle switch to trigger the relay and let the relay handle the amp draw of the fans.

10-20-2002, 11:01 PM	#1
HvyChevy454 Slowly getting CRSS... Join Date: Jul 2001 Location: Lutz, Florida Posts: 656	funny electrical problem ever since my father and installed eletric fans, whenever i go to turn the truck off i can turn it off take the key and be ou tthe door before it will kill the motor. If i un hook the fans it shuts off immediately? __________________ -Nic Lutz, Fl My Team Website The Heavy Chevy Website ------------------ 72 Cheyenne 10 LWB GM 12-bolt 3.08 w/ Auburn Posi 91 454 Edel Performer RPM Intake 750 cfm carb Comp Cam 268/.495 Hedman Headers Dual 3'' Exhaust 71 Cheyenne 20 4x4 Fact. A/C PS PB Tilt Currently in the works... Speak Softly and Carry A Big Block... There is No replacement for Displacement... "If everything seems under control, you're just not going fast enough." - Mario Andretti

10-21-2002, 12:59 AM	#3
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	ya what longhornmail said, Go to radioshack and ask them for a big mofo of a diode one that can handle a few amps of juice __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life

10-21-2002, 07:25 AM	#4
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,771	IF you run relays with your fan you wouldn't have that problem.As soon as the key is turned off the cicuit to the fan is interupted so it doesn't feed back into the system. you can see the ones I used in the bottom left corner of the fan shroud,One for each fan. __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE Last edited by BobbyK; 10-21-2002 at 07:31 AM.

10-21-2002, 09:43 AM	#5
Lippyp English Chevy Owner Join Date: May 2002 Location: Shropshire, UK/ Lot, France Posts: 1,848	Definitely make sure your fan is wired through a relay. I have a single fan on my truck fitted by the previous owner and it wasn't wired via a relay. It was switched by an illuminated switch on the dash which would light up even when the fan was off as the fan windmilling in the ram air as you moved generated enough power to light the bulb. I also found when stuck in traffic one hot day that the connections at the back of the switch were too hot to touch, so could easily have caused a fire. Fitted a relay and a new fused supply from the battery and all is now fine. For the sake of a couple of dollars you could lose your truck to an electrical fire, sort it out now! __________________ Phil '67 C10 long fleet. 350/TH350, 4 bbl Carter, K&N, Dual exhaust, loads of stuff coming soon 2001 S10 Blazer Daily Driver, bone stock 4 door 4x4 with manual transmission

10-21-2002, 09:53 PM	#6
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	A quick fix is to change your power source. Sounds like you got it wired through the ignition. __________________ The more I learn about women, the more I love my truck.

10-20-2002, 11:11 PM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	The fans are turning after the power is shut off, and they produce enough of a charge to fire the coil. THey act as a small generater. You need some kind of a diode (think of it as a one way check valve for electricity) that will stop the problem. It is a common thing when installing electric fans.

10-23-2002, 02:00 PM	#7
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,771	I run my fans direct from the battery with two 30 amp ciruit breakers(one for each fan). On startup the fans can requiere a good deal of amps to start turning(depending on fan of course).The circuit breakers are self resetting so there is no need to change any fuses. Wiring high amp peripherals such as electric fans without relays and fuses or breakers is not recommended.A run-of-the-mill toggle switch is just not designed to handle the full amp draw of an electric fan.Use that toggle switch to trigger the relay and let the relay handle the amp draw of the fans. __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE



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