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The factory configuration allows the A/C compressor to run in all positions except off. There is nothing you can do with the control switches or wiring that would change that because it's already enabled whenever it's on..
I always look forward to your posts because you have great insight on this stuff but I've got to disagree with this. The vent selector **** on my 99 and 01 TAs are colored blue for the top and blended vent setting but white for the feet only. [Amber for the defog, defog+feet (which will run the compressor)]. I've set it to cold blowing at the feet and the compressor doesn't kick in with this setting. I guess I could just meter out the contacts in all the control settings to get to the bottom of this.
But yeah, I'm not looking to manipulate/bypass anything beyond the controls.
Last edited by thingthatgoes; 09-23-2016 at 07:24 AM.
Well, I haven't had my Trans Am for several years so I can't try it but the schematic shows that the A/C request signal is available to the PCM in all switch positions other than "Off"...
I know that A/C is available in the Max, Norm, Bi-level, Vent and Defrost positions so I don't see why Heat/Floor would be the only position that wouldn't have it.
Interesting. Maybe it's the print or maybe there's different variants of the climate control? Mine doesn't look like the selections showing on the print. For example I don't have a "heat" or "vent" selection.
Notice the options are a bit different than the print.
The colors seem to indicate when the AC runs. That's consistent with my playing with it anyway. I'll let you know when I get to open it up if I find anything out.
Edit: also, notice the amber for the 2 defog options. The compressor will run for those 2 and I have used the defog+floor option to cool off my tootsies.
That's fine with me. I like to take the tops off in moderate weather and get cooler air at my feet. There's enough air circulation otherwise.
Good reason. When I ever get an abundance of free time... I want to pursue a cold air mod for the vent also. I've found that the vent intake in our hood cowl heats the air (with engine heat) substantially on a cool day so the vent air is much hotter than the outside air. (As a result, I use the A/C a lot more than I would like.)
I recall in the fine print of the GM Service Manual, that the Selector Switch is a compound unit. It has multiple layers and has a combined vacuum valve/switch (for the duct vent doors) and electrical switch. (for the A/C command) I've always wanted to tear apart the switch and see how it looks but didn't want to risk having to get a new control panel in the event of failure...
So, I would expect that it would be VERY challenging to modify the actual switch to behave how it is desired here. The path of least resistance is probably to add a lighted push-button switch to manually command the A/C on/off (like many modern cars) and then also let the existing switch do the same. (So, you wouldn't be able to select defrost and not have the A/C on.) That switch would just manually jump the brown to green/white wires when you'd select it on.
Well, I haven't had my Trans Am for several years so I can't try it but the schematic shows that the A/C request signal is available to the PCM in all switch positions other than "Off"...
I know that A/C is available in the Max, Norm, Bi-level, Vent and Defrost positions so I don't see why Heat/Floor would be the only position that wouldn't have it.
Can anybody confirm the source voltage for this circuit? I greatly appreciate the completeness in including the internal circuitry which makes it easy to understand but the question remains, does it use 12v system voltage or the 5v sensor reference voltage? I would assume 12v but that can be dangerous.
You can't see it in the cropped image I posted before but that circuit #241 is powered via the 20A HVAC fuse (#6) in the instrument panel, so it is definitely 12V.
09-23-2016, 06:43 AM
