I just finished installing new electric fans on my 69 Malibu. I used a non-adjustable Thermostatic Fan Control (Hayden part #3652) for the wiring, which is set to come on at 185 and go off at 165. The sensor probe screws onto a disc which the manufacturer calls a snap switch. One wire goes from this switch to the relay, and the other goes to the ignition wire or toggle switch.

Got everything together, fired it up, let it heat up and no fans.

I double-checked the wiring and then put a jumper wire between the two wires that connect to the sensor probe's "snap switch". Fans start spinning. I moved the probe closer to the inlet and started the car. After it heated up, still no fans.

Does anybody have experience with these types of probes or the accompanying snap switch? Is it probable that either one of these is bad or is there something else that I should look at?

I don't care for probe style controllers. Where did you get it?

Did you test it?

Stick it in a pan of water on the stove and check it with a meter to see what temp it closes at.

Okay, I tested it in a pot of water and the water got to boiling and the contacts didn't close. I returned it to the store as defective and got a new one. Tried it in my "test pot" and same thing. The radiator is aluminum. does the probe have to have a solid ground?

Got it solved. I think it may have been a ground issue. I also installed a bypass toggle under the dash in case there are any other issues with the sensor. Took it for a test ride around town (it was very hot today) and it runs a little hotter than with the clutch fan, and the fans kept cycling off and on. I hit the bypass switch and let them run full time and the temp came right down.