A/C Question Please.

[Huney1]

Gary sez, "From reading the posts it seems that the opinion here is that the internal (closed pressured refrigerant) system somehow senses cabin temperature and/or humidity and cycles the clutch." When you have your AC checked they take a thermometer and stick in the vent and best I recall it should be putting out cold air near 40F. Now, as for the cabin temprature sensor, it would probably be near the cooling coils aso known as the 'evaporator' and when it reaches a certain temp it shuts off the compressor. If it didn't the evaporator coils would freeze up and zilch cooling. Thus, take a AC with insufficent freon and the compressor would run longer and as the freon level (pressure) diminished the compressor would run longer because the inside sensor was not happy and called for more cooling

"The clutch only cycles in response to the external thermostatic cabin control and (in some models) the cabin humidity sensor." Hmmmm . . . I'll have to give that some thought. By external I assume you mean the prevailing outside ambient surrounding enviroment. As far as ambient humidity OR temprature is concerned, the AC knows nothing about ambient enviroment and works strictly from temprature readings the sensor takes INSIDE the cabin at OR NEAR the evaporator coils, or it may be in the duct work that carrys cool air to the cabin. The temp setting on the dash, digital or analog, sets the temp INSIDE the cabin which has been the case since way back when vehicle AC's first hit the market before computer circuit boards existed.

Here's the way I see it: If it worked as you say we would have no need of an inside temp control because the external sensor would be overriding the temp we set inside according to the external ambient temprature and humidity. Seems it would take a computer program to read the temp we select, (which, by the way, has nothing to do with humidity), then read the ambient factors then compute what cooling we need inside. Maybe I'm all wrong and later I'm calling the AC shop and ask them and if I'm wrong I'll eat a double helping of Crow. I will grant you, a Mercedes 'prolly has a much more sophisticated AC system than our humble Tauri, but basically I believe they all work the same.

Good discussion and learning thread here and thanks for putting my old brain in overdrive at this early hour.

[Gary1234]

I think I'm being missinterperated ... let me try again.
There is only one control line that operates the clutch ... all temperature, humidity and refrigerant pressure controls are placed in series along this +12 volt control line. What I am trying to say (not very well), is that the clutch only responds to the control line ... there is no reason to suspect the clutch is cycling (if it is) for some reason other than in response to the cabin temp/humidity controls or low refrigerant level.


By external, I mean external to the pressurized refrigerant system.
I think we may be saying the same thing in different ways.