radiator fan control wiring

[rja]

so my fan comes on when the engine starts. i can turn the ignition off and on really fast(engine keeps running) and the fan quits. rev the engine a little and the fan starts spinning again; tap on the relay and the fan starts spinning again. this car came equipped w/a dealer installed a/c system. it looks like it has a wire to the fan relay to energize it when the a/c clutch is energized. i should add the a/c system is NOT charged and inoperative.(although you can kick the a/c clutch in by turning on the switch). the thermoswitch in the bottom of the radiator 'seems' to have no effect on fan. do i need a new relay (sipea t-7810), a new thermoswitch, or leave it alone and let that baby run? all answers and inquiries welcome 'cuz i haven't a clue!

[RRoller123]

what year is the car?

[rja]

sorry 'bout that guys; it's a '74 1800. and that a/c compressor is an old york, big as west texas, placed forward of the carb. put a squeeze on it the other day and it held better than 20" vacuum for a coupla hours. i'm hopin' i can get this fan situation figured out; be nice to have a/c for the big tx. heat coming next year!

[RRoller123]

I am not familiar with how these would be wired when an AC is involved, but the basic circuit is pretty simple, and the fan should not come on automatically just with the engine started, that is odd for sure. Here is a basic wirinfg diagram for my 1980, I assume it would be similar for your 74 (?) It sounds like the intent was to have the fan come on when the aAC compressor is running but it is not accomplishing that. Could you diconnect the AC wiring and see if the fan operates normally without teh AC in the circuit? It should come on around 190F, run for a minute or 2 until the temp drops, then cycle like that repeatedly.

[rja]

thanks for posting that; not too good at reading wires, though! the aftermarket a/c has LOTSA wires w/it and it's a good idea to try to take it out of the equation to figure the problem. by tapping on the relay, i can get the fan to run, so it's suspect; when i can find one, i'll try component exchange. already have a temp sensor for the radiator to try and plan on changing the thermostat too when i drain and flush the cooling system. i kinda figured that was how the system operated; just don't ever hear the fan quit while going down the road. and the temp seems to be kinda on the low side, too, since umplugging the hi temp sender.

[RRoller123]

A lot of these cars have had POs wiring up a fan over-ride switch under the dash, I suppose it is possible that yours was wired up to run all the time? Or that there is a switch somewher that has been left in the "ON" position. This is not as far fetched as its seems, that is exactly the way my car came, the fan was always running, and I discovered the switch under the dash in the "on" position. New sensors and corrected wiring, along with properly burping, got it all operating correctly, although I left the over-ride wiring in place just in case it was ever needed.

[rja]

interesting. no override i can find. once i get a new fan relay, i'll be able to switch components and see if i can track down the fault. maybe thanx for posting.

[RRoller123]

Others may want to chime in on this. My question would be, is it normal in an aftermarket AC system to have it turn the fan on when the compressor is running? I can see where this may be necessary on a small engine, but if it is not, then RJA could just rewire the simple fan circuit to the schematic and be done with it. (?)

[rja]

hey-found the jumper that makes the fan run constantly. had to replace the radiator switch (it was fubar). now the fan runs like it should. the a/c is wired so that when the a/c thermostat is made, and the a/c fan is on, the radiator fan is on. drop either one out, and the radiator fan runs normally. drop the a/c fan out and the a/c comp clutch kicks out. i think this is how it should be wired?

[FabriziaSpider]

I'm having similar difficulty, my fan is receiving power but for some reason doesn't turn on when it's supposed to. I have changed that little censor at the bottom of my radiator but for the life of can't seem to understand why it's malfunctioning. I don't want to have my cam re-machined again. Anyone got any ideas? Fan has power and sometimes turns on?

[So Cal Mark]

the ground side is switched. Jump across the terminals on the sensor to check if the circuitry and fan are functional. If the fan runs, then either the sensor is not getting hot enough or it's malfunctioning. Air in the cooling system will prevent the thermostat from opening and the sensor will not get up to temp