Arrrgh...cooling fan problems again

So...I have manually operating cooling fans in my car that I control with a switch. I was told by previous owner that they wouldn't kick on, but I think the temp. sensor that controlled the fans was clogged with coolant junk, as I discovered when flushing the system. The problem is the switches keep burning out. I only need to drive with one on since I have a 180 degree thermostat, high flow water pump, and larger capacity radiator. I also disconnected the a/c belt because it's no longer in working condition.
So far I have gone through two sets of switches on the manual controls. The switches draw current from one power line with a 30amp fuse. The fuse blew when I was only operating one fan. Should I try to reconnect the fans back to their original factory connetion or do I need to rewire the manual system? Any help would really be appreciated, thanks.

Take it from someone with 30+ years of electrical / electronics experience: NEVER use a switch to control a high amp load!!!!! Use a switch to control a high current relay, and use the relay to carry the high current to the load!!!! Get some 30A fog light relays for about $4 each from the parts store. They have 4 terminals. 2 are the relay coil, and 2 are the contacts. THe coil terminals are interchangable, as are the contact terminals. Wire the 2 contact terminals where you have your melted switch now. I hope you used at least 10 guage wire, right? Mount the relay(s) under the hood, and run the 10 ga wire from the batt terminal of the starter solenoid to the relay contact terminal #1, and from the relay contact terminal #2 to the fan power wire. Be sure to use a 30A blade type fuse or a fuse link in the line as close to the batt as possible. Now for the relay coil wiring: Find a hot in run wire under the dash, and run it to a switch. You can use a small switch, as it only has to carry .1 Amp or so. The other switch terminal goes to one relay coil terminal, and the other relay coil terminal gets grounded. Any small gauge wire will work for the switch / relay coil wiring.

BTW, my stock fan control system works perfectly, but I think the EEC waits until the motor is too hot to activate the fans. I left the stock control system intact, and piggybacked a second set of controls. I have the main fan under both fully manual control and under control of an external fan control thermoostat ($20 at any parts store). I have the aux fan wired to come on whenever the A/C is on (so both fans run with the A/C on). With this setup, I have NEVER seen the temp gauge go past 1/4 of the way up, even in 100 deg summer temps.

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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 20 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 00 Windstar (wifes vehicle)

[This message has been edited by Jeff K (edited 10-03-2002).]

Just to chime in with my nickel's worth of free advice [Image: biggrin.gif]

My stock fan switch broke. So I used to run the same setup as you - took power from the fuse panel, to a switch in the dash, then out to the fan. The switches blew frequently (lighted ones blew even faster) due to the high current.

Then I did as Jeff mentioned (btw, his advice is worth a lot more than a nickel [Image: biggrin.gif]). I have a 30A relay, wired as mentioned above. Only a small current goes to the switch, as it is only turning the relay on and off. It never sees the 30A feed. I'm using a 30A circuit breaker (a few bucks from AutoZone) as well.

Only problems after having this setup for a year: first I kept tripping the breaker - turns out it was a bad breaker. Then the relay (it was used to begin with) developed a loose contact, so I had to replace it.

Phil

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86 TC 3" Exhaust w/ Cat, 17 psi, 1.5" lower, Vovlo intercooler, Saab 900 cooling system
73 Austin Mini 1275

One way i fixed my over heating problem was to simply use another relay to turn on the second fan when the first fan was turned on. It is important to use the power that is going to the first fan as the signal (acting like an on/off switch) to activate the relay and then use power from the battery to be switched by the relay to the second fan. This worked very well for me and the fans dont run as long as the single fan (obviously). Also if the first or primary fan isnt turning on the fan at the correct temp then get a new electrical temp sensor near the firewall. If this doesnt work it could be a computer problem, thats what happend to me. The computer supplies a ground to the sensor, trace out the wire using a manual that goes to the computer and cut it and just ground that wire. After this is done whenever the sensor gets to the correct temp it turns the fan(s) on. I did this on a previous TC that i had, it was a while ago though so i forget which wire of the two that i grounded.

Thanks alot guys. I'm going to try your suggestions, and I'll let you know how things turn out.

Kristen