50C - Open
85C - Open
90C - Open (if this is max temp), Closed (if switch was closed by higher temp)
112C - Closed

Think of a dual float activation on a pump. A high float turn the pump on, a low float turn the pump off. Same basic concept here.

If it said 93C then that's when it would close and open (like the orignal switch closes/opens at 112C). If it was reverse, 88/93C, then it would close at 88C and open at 93C (usually used on multiple pin sensors to trip fans to higher speeds).

I'm guessing the switch in question is a radiator fan thermoswitch. If it was a tolerance range (as you're thinking). The fan would turn on at somewhere between 88-93C, and if it was cold enough out, shut off right away. They have these switches turn on at a higher temperatures and then hold to a lower temperature. This keeps you from wearing out the fans/pumps by NOT cycling them on and off all the time.

These thermoswitches are pretty accurate anymore. Some can get within 0.1F of a temp.


Audi's been using these after-run systems for years, and the staged switches work by turning on high and shuting off low (to save the pump). The 10 min limit is really only there so you don't drain the battery if the switch fails. The bad thing about the S4 system (aside from the high temp switch) is that it doesn't run the coolant through the heater core. :(

Really, the current "fixed" temp switch could be why so many of the pumps fail. They cycle on and off too fast. This is actually the first Audi after-run system I've seen with a "fixed" temp switch.

Current Audi Count ---> 5


Previous Audi Count ---> 7

In spite of dealers; I still love Audi :-)