Diagnosing a faulty cooling fan (specifically the #2 cooling fan switch)

Hi everybody, thanks for having a read and any input!

I have a 2002 Toyota Avalon with non-operational dual fans and as a consequence, overheating that I am working on.  So far, I have checked relay and fuses, and hot wired the power and ground onto both fans (also jumpered the fan switch), and they both worked.  With the engine warmed up, I measured the resistance at the coolent temp. sensor, and it was between 200 and 300 ohms, which I believe is within spec.  I moved onto the #2 cooling fan switch, which is in the radiator (#1 is on the thermostat housing).  Here is where my main question lies (although still interested in the overall issue):  So, I took the the switch out (it is a two terminal switch), hooked up my DVOM, lowered it into some boiling water, and measured no continuity or resistance.  Now, I'm thinking, problem (at least one) solved.  I went to the junkyard, got three used switches, did the same bench test, and got nothing.  Now, I certainly know that they all could be bad.  But, on a good two terminal switch, with the two leads from the DVOM connected to the two terminals on the switch sitting in boiling temperature water, the switch should close and get continuity, correct?  The logic seems sound to me.  I just don't know if maybe I am overlooking something, or perhaps it somehow works differently with the two switches.  Side note:  I also picked two #1 fan switches (which are single wire switches) from the junkyard, but have not had time to test them.  If I have time, I will check that tomorrow.  So, what do you guys think?  Am I overlooking something?  Thank you, all.

Michael 

Nothingman wrote:

But, on a good two terminal switch, with the two leads from the DVOM connected to the two terminals on the switch sitting in boiling temperature water, the switch should close and get continuity, correct? 
 

Here's a chart I that I found in SI. According to it, you should always have continuity. 30K Ω, at -4°F. dropping to 0.1K Ω (100 Ω), at 212°F.

 

Have you checked the continuity of your test leads, by touching them together?
 

Thanks.  Interesting.  And this is on the fan switch, not coolent temp sensor? Because on the sensor there is resistance like above. I thought the switch is open/closed. There are some videos showing this test.

Edit:  And yes on the probes.

Nothingman wrote:

Thanks.  Interesting.  And this is on the fan switch, not coolent temp sensor? Because on the sensor there is resistance like above. I thought the switch is open/closed. There are some videos showing this test.

 

My apologies. It looks like I opened the wrong chart.

You are correct. They should be open/closed switches. Not resistors.

Ok, cool.  Well, that makes me feel a bit better (new switch has already been ordered).  It is amazing that three out of three switches were faulty, and that potentially, people junked their cars because of it.

Thanks Chad.

To anyone who may be reading this with a similar question, I just learned something valuable, and hopefully, it may benefit you.  If you are performing this test at altitude, such as in Denver, where I am, the boiling test will not work.  Because of the altitude, water boils at a lower temperature, and will not reach the 208 degrees necessary to close the switch.  I just used a propane torch on the switches, and they closed.  Lesson learned.  Good luck.