Radiator Fan Switch Question

[dsnyder]

1978 Spider: As part of getting Air Conditioning working, I am adding a relay to work the fan motor. I need the fan to turn on whenever the AC compressor is running...

The radiator fan switch appears to be a negative ground switch. I'd like to make the relay postive activated (AC compressor wire goes to the relay activation and the fan temp switch also goes to the activation)... Pretty simpy wiring with the addition of one Diode.

So now my question: Can the existing fan switch be converted to take positive wire in/positive wire out without grounding out when it clicks closed? Will it somehow find a ground through its threaded connection to the radiator or is the switch isolated from from the switch body?

Thanks in advance-

Dave

[BEEK]

why not use the relay to switch the ground leg of the fan as well, much easyer. use the signal (positive) from the ac to switch the relay.

[dsnyder]

I probably don't understand exactly what you are saying but to try to clarify... there are two instances when the fan needs to run.

1) Whenever the AC is running regardless of radiator temp the fan needs to run.

2) When the radiator temp goes up to 190 degrees whether the AC is on or not.

As you describe it, I don't see how the two situations above could be achieved as the radiator trigger is on the negative side and the AC trigger (Compressor clutch line) is on the positive side.

[BEEK]

ill consult my wiring diagram manuals and send you a diagram. i have to look at the original setup,

[So Cal Mark]

it would simplify the wiring if you use the relay to switch the ground, then no diode is needed. You can run a parallel circuit with the temp switched circuit

[dsnyder]

Mark, I see what you are saying having it click to ground in parallel. If I have it all up and working switching to positive with the diode in place and all, is it worth rewiring again?

One of the benefits is that I ran a heavy gauge wire from the positive battery cable on the starter as the feed for the fan.

I really just need to know if the temp sensor can work as a positive switch without shorting when it heats up. I tested it cold and there is no continuity to ground when cold.

Dave

[So Cal Mark]

the switch is not internally grounded, it merely closes the contacts when up to temp