Ok, I can't take being stupid anymore when it comes to my PCM. Here are a few dumb questions that <After the great Cupholder thread> I am no longer afraid to ask, lol.

1.) How in the world do I turn off the Auto climate control without having to click click click down the fan speed control to zero. Just hitting the Auto button when it's on doesn't seem to turn it off?

2.) Why when I hit the "Front defrost" button does heat blow out regardless of how cold I have the temp set at? It's always hot air even if I turn down the auto control to "Lo".

3.) Also when I run the climate control I see the little "snow flake" button come on even when I have the heat set very high. I'm not sure if the AC comes on but I try to manually turn the snow flake off so it doesn't lug the engine <like if the ac is on>. I don't know if it even does, but seeing the snow flake up there when the heat up high bugs me lol.


Ok ANY and all TIPS SUGGESTIONS or just hints to get the most out of this system would really help. So lets hear it PCM vets, what can you give us?

 

1) No other way.
2) Heat is for cabin temperature, defrosting/defogging is more efficient with heat
3) Snow Flake means that AC is on, hit the ECO button to turn it off. AC removes the moisture from the air, and isn't relevant to temperature.

These are common to all vehicles, not just Porsche. Also, PCM doesn't control heat, it is the radio/nav unit/info unit.

 

There are several things at play in the HVAC (heating ventilation air conditioning) system of the car. In general one can run airflow through an air conditioner which can generally cool and dehumidify the air, and run air through a heater which heats up the air. The two can be used together.. so you can run air through an air conditioner and then through a heater. Doing that gives you DRY and WARM/HOT air. Just the AC gives you DRY and COLD air, and just the heater gives you (generally) MOIST and WARM air.

Now heat is free.. in that the engine is producing it anyway and turning up the thermostat in the car, just directs some of that heat into the cabin interior via the ventilation system.

The air con isn't free. Activating the compressor puts a load on the engine and steals a small mount of power and increases fuel consumption a bit. But you can add free heat to that to get the air dry and the temp you want.

So for the 997(.2 in my case) the default "AUTO" setting has the car running AC to maintain the humidity and then the heating is on on top of that to balance the AC to get the temperature selected. If the air is dry (not a cold rainy day for example), you can press the AC OFF (probably the ECO button on other variants) which turns off the AC part and you just pull outside air and heat it. If the window fogs up, you want to then turn the AC back on to dry out the air.

As mentioned, a snowflake typically indicates the AC compressor is on (dehumidifying and cooling the airflow).

Now to the questions:

1) To turn the system OFF (ie no airflow, just stagnant air) hold down the fan speed button until the fan speed goes to OFF. No need to click-click-click... just hold and wait a second or two. The reason there is no 'off' button is that its thought you would typically want to set the car to some internal temp and then have the ventilation system blowing in fresh air from outside (or recirculating inside air) just to keep the inside air moving and relatively fresh. Just set the temp you like, fan speed auto adjusts based on how far off your desired temp the interior temp is.

2) Front defrost = hot air. Yes, that is to be most effective. Warning: more science. Hot air can hold more moisture than cold air. Thats why one refers to relative humidity - we speak of how much water is in the air relative to how much it could hold.. its temperature dependent. Now the front defroster is all about getting all the moisture off of the front window as quick as possible. To do that, the best way, blow hot dry air over it; that is quicker than cool dry air, and better than hot moist air. So if you select defrost, the cars system picks all air out the front vent, turns on the AC to dry the air too, and blasts it at the windscreen.

Once the window is cleared, you can turn off the front defroster, and just keep the ventilation system running with the ac on (auto mode), to maintain the dry interior air at the desired temperature.

3) So in auto mode, as mentioned the AC comes on to maintain humidity, regardless of the temp you have selected. If you know the humidity control that the AC is providing isn't needed (say your in the desert, know its dry, or its so cold there is little moisture in the air) the just turn off the AC (AC-OFF or ECO etc button).

Hope that helps.

 

That is AWESOME! Thanks to both the OP and to you for this.. wow. Good stuff.

 

Thanks for the input guys!

 

rep points!

 

this is good stuff... And another little tidbit I learned completely by accident .... if you have an I-pod plugged in, when you hit the "disk" button, it actually gives you the menu for the i-pod.

 

Yeah that not quite obvious learning was new to me too at the time, that the DISC button selects between the multiple other audio sources (DISC, IPOD, AUX, USB, etc) depending on what options you have and whats plugged in. Its like the radio button choosing between AM-FM-SAT.