What does the yellow light on the A/C button mean?
Similar Questions: How do I know my A/C is on?
"When the yellow light is on, the air conditioner delivers cold air when the interior of the car is hot and then gradually tempers the air as the interior of the car cools down. This is done by gradually changing the temperature set points at which the compressor cycles to higher temperatures."
"To see exactly how this all works check out the graph at the bottom of page 24-4 of the "Technical Information Manual"."
Most people believe that the green light means the air conditioner compressor stays on all the time. This is not true.
From a post by Lorrin Barth:
"When the green light is on the air conditioner cycles off when the oulet temperature of the evaporator drops to 37 degrees and cycles on when it rises to 39 degrees. In other words, cold air all of the time. Of course, as in really hot weather, the evaporator temperature may take a long time to drop to 37 degress, and this is going to depend on the condition of the system too, making you think it never cycles.
So, as you can now see, the compressor cycles in either mode. To see exactly how this all works check out the graph at the bottom of page 24-4 of the "Technical Information Manual". "
Why does the A/C come on, by itself, when I turn the defroster on?
This is peculiar to 2G DSMs. Likely the factory installed this feature to ensure that the defrost air is dry. Trying to defrost a freezing windshield with humid air does more harm than good, and blowing snow can easily get into the fresh air intakes.
It was previously posted that the rationale for this 'feature' is that disuse of the A/C feature during winter can lead to premature seal cracking. Having the A/C on with the defrost ensures that the A/C system stays "active" and keeps the seals properly wetted. This might be considered suspect since chronic A/C seal failure is not known to be a problem on 1G DSMs - even Canadian ones.
If you hate it, you can remove the little tab on the vent dial that is responsible. Essentially, there is a small tab on the A/C selector knob that automatically trips the A/C if the defroster is selected. Breaking off the tab "fixes" it.
The Last Word: Your experience may vary, but the only reason I keep A/C in my car is to dry the air and keep the windows fogging up in rainstorms.
While it requires a bit of trimming to get to fit, everyone seems pleased with the product. Here are the results of google search for stockinteriors.com dsm which provide many forum links to people who have used this service / product.