ok, I'm trying to hook up a new a/c auxillary cooling fan, and I'm not getting the voltage to run it. the high pressure cut switch burned out, so I bypassed that, and the rad temp switch I jumpered the cables also. I'm only getting 2-3 volts at the fan.

I've pulled the the fuse panel. at the #7 fuse from the top, I'm not getting any volts across the terminals with the fuse in or out. from the bottom at #7 One of the 3 wires has 12 volts. The other two have 0 volts at ground.

the #7 fuse seems to be connected to the #18 fuse some how.

I do want the fan to run all the time. I do live in Miami, so its hot at all the time.

Do I need to just yank the hot line and add an "add afuse" to the fuse block?

I also trace the line back to the firewall, and at the fire wall Im getting 2-3 volts as well.

I'm talking of the grey wire with the red stripe.


Any and all help would be appreciated.

 

I looked through the wiring diagram (I could scan that in if I can get a scanner, but tell me if you need one, my diagram is for and 89 700). The diagram shows a red wire running from the battery to what they call the "positive terminal" One red wire leave that terminal and goes to a "relay circuit" they call it the "#30 circuit". I think that this is one the bottom of the fuse box, but I not sure.the #30 circuit connector should have 6 connectors but only four of them are used. There should be 3 red wires and one red and black wire the second thinnest wire should be for the power windows, but it also feeds the #7 fuse slot for the fan. Power runs through the power window relay at contact 30 and comes out contact 87. It is switch by the relay (I don't understand why). There are two #87 contacts on the relay, they are both switched, feeds power for the windows (yellow-red wire) and the other goes to the #7 fuse (gray-red wire). It's strange that there is no diagram for a car without power windows. The rest of the circuit is simple. From the fuse the gray-red wire continues to the switch in the radiator, to the fan and then a black wire to ground. So let me lay it out:

Batt "+" >red wire> positive terminal >red wire> #30 circuit >red wire> power window relay >gray-red wire> #7 fuse >gray-red wire> switch >gray-red wire> fan motor >black wire> ground.

That's what the wire diagram says for 89 740s. Hopefully you can find those parts and trace back until you find your voltage drop if you car is wired like mine. Good luck.

 

Just run a new power line off the battery, feed it to a switch you can put on the dash, then to the fan. You can get ground with a self tapping screw somewhere. You just have to remember to turn it off.
You could jumper off a known fuse that does not have power until the car is running, like the cig lighter, however you would need to up the amperage a little on the fuse but as long as you dont use the cig lighter it should not be a problem.

 

big daddy, I was thinking of doing that. if the #7 fuse block is shot. The good thing is the ground for the a/c fan is on the same grounding point as the headlights. right there on the inner fender next to the battery. IF that happens, I think I'll run all new wire. But let's see if I can keep the real circuit. I realy don't want to remember to switch the fan on and off all the time.

 

dont blame you not wanting a dead battery, I would forget myself even if I used a lighted switch LOL!

 

Beardog, the real issue is the 740's NEVER were wired for the aux fan to run full time with the a/c. They were wired to the absolutely worthless sensor in the radiator. By the time that stock sensor completes the circuit, the motor is already too hot. I'm guessing you want the fan to run when the compressor runs to reduce head pressure and make the a/c more efficient in stop and go traffic, right? What I do, since there is no pre-existing circuit for it, is install a relay on the driver side near the battery (my cars are turbos), fuse the feed wire from battery to relay and use the wire going to the compressor as my signal wire on the relay to trip the fan. Consequently, when my compressor runs, the aux fan runs...no need for a switch on the dash. Takes about 30 minutes to do it right w/ soldering and heat shrink. Just one solution.

 

allright, I ran some the volt meter from the the #30 on the relay to ground and good voltage, also from 87 and 87 b to ground. also good voltage. then I ran either side of the fuse to ground, and good voltage.

the problem seems to be the wire from the fuse through the firewall. At the junction at the engine side of the fire wall. the wire had 3 volts.

Is there an easy way to get this wire through the firewall? Or actually, the new wire through the fire wall? Its down in the center of the firewall behind the engine? and I am not so sure where it appears on the interior side of the wall yet.

 

Visit this link at the very bottom is the information in a schematic form, that Swiftjustice44 is providing.
http://personal.linkline.com/dbarton/FanDiagram/

Good Luck

 

sorry for the revive.

I would like to thank you all for comments. Darkdelta, and swift justice, I would like to thank you both for the schematic. I used the last relay map and hooked the system to battery and the ac compressor power source.

Just could not get the fan to work with the original wiring. Somewhere between the fuse and the firewall, it all went kablooey and lost the voltage.

once again, thanks