I know where it is on a 1st generation, but can't find it on my S4. Thanks for your help.

 

I presume you're referring to the actual temp sensor?

The "logicon" controls the temperature.
The temp sensor may be inside it??

There is a "thermoswitch" on top of the evaporator box, but I think that's just to detect iceing.

There is an AC section in the S5 manuals.

 

Do you mean the thermostatic expansion valve? The one that controls the refridgerant flow into the evaporator? That's at the entry to the evap.

 

The only thermostat is the one nopistons mentioned, with switches the compressor on and off based on evaporator temp. There are no HVAC-related air temp sensors anywhere.

 

my 84 '7 had a thermostat under the passenger side of the dash and it sensed the cool inside the cabin...you could bypass it and the compressor would run all the time...I'm surprised the S4's don't have one. I'm going to start a list of the items the FSM does not cover. There evidently is not a thermostat inside the car but there have been some other items left out of the FSM. Thanks for your help.

 

Ok...I think we have a misunderstanding based on terminology or description. In the FSM (I found this just now) there is a section in wiring under Heating and Air Conditioning (50-64) page 66. IT is listed as AC-04 and is called A/C Thermostat on a previous page. You have to take out the glove box insert and it sits on top of the evaporator casing and has two wires running to it. It may very well switch off the compressor based on temperature but these things malfunction, as mine has and shuts the compressor down before it gets too cold....I thought it was an air temp sensor...my mistake and my misunderstanding....I put a jumper wire in and will freeze ya in a few minutes. Of course I have to kill the a/c with the switch every few minutes to keep the coil from iceing but it will do till I can get a new thermostat....
thanks again guys and as usual you are right on.

 

Cycling the compressor on and off may be designed in to prevent the evaporator from freezeing up, (on the outside of the evap) because if it does freeze up, air cannot flow across/through it because the ice blocks the air flow, and you get no cooling inside the car. On my everyday car (Ford) the compressor cycles on/off about every 15 seconds, for just that purpose.

 

That's how all automotive A/C systems work.