AC temp switch
 

Is there any way to test these out of the car? This is the switch mounted on the drier which tells the aux fan when to run.

Is the switch currently out of the car? If not, is your a/c system charged?

I can't speak for your SD, sorry, but my cars use a pressure switch to turn on the auxiliary fan(s) in low speed. The trip point is ON at 16 bar (232 psi) and OFF at 12 bar (174 psi). To test that outside the car would require some kind of pressure-generating rig that would be compatible with refrigerating fluids, since the test rig would contaminate the switch in a small way. You might even be able to use a modified pop tester for injectors.

If your car uses a temperature switch then I am out to lunch.

Jeremy

I want to test a second used one that I have. The one in the car I assume not to be working because the fan never comes on. Fan works fine when shorting terminals leading to switch.

You should have no continuity thru the switch at room temperature. If you put the switch in a pot of warming water on the stove, the switch should close at around 125*F.

If that is the exact switch that you have, keep in mind that you will loose your refrigerant if you remove it from the r/d.

That is a very common sign of low refrigerant. Maybe try a hair dryer or heat gun on the in-car switch.

Will report back.

the aux fan temp switch can be removed from the charged system. the pressure switch can not.

I must have been completely mistaken in thinking that there were two different types of temp switches!!! And I was so sure that I knew what I was talking about. Thanks for setting me straight.

Just one question: Did you read post #6? (With special reference to the part about the telltale hiss.)

That's what i first concluded from readings on the web, yet the hiss of escaping refrigerant suggested otherwise. Unless there's a valve type mechanism on the r/d that engages once the switch has been screwed out far enough. Or the AC shop slapped in some cheapo aftermarket r/d which has no barrier between switch and refrigerant.

Could not get continuity at + 125F. Also no luck with the one on the car though less conclusive - can't be sure I'm getting it hot enough.

There are two types of temp switches. One connects through to the refrigerant and one does not. (Some aftermarket receiver/driers have ports that will accomodate either version.) We both know which version you have.

On my '82 300D, engine compartment heat, on a really hot day, will occasionally trip my switch, even with the a/c not in operation.

It would just be annoying if it'll still not work after putting in a new one. Could there be an issue with the dryer?

None that I could envision.