air conditioning

[x2xtreme360]

Any idea why when the venting toggle is on the defrost of defrost+floor, the air conditioning light comes on? It's always done this, but I don't know why. Even if the AC button is off, when you select either defrost or defrost+floor, the AC light illuminates like it is on.

[Bernie3]

It's to control moisture and keep the windows from fogging up.

[Zembonez]

^^^ What he said. The compressor runs in order to dry the incoming air. If it didn't, the humid outside air would fog up your windows. It also serves to keep the AC system working occasionally through the winter. That keeps lubrication in the system evenly distributed.

[x2xtreme360]

Interesting. I think this is the only car I've found that does this. Either that, or it's just never obvious to me. Idk how much I like the compressor running practically all the time in the winter. The extra load all the time. For now I have a bypass belt due to a power steering failure, and it's not going around the compressor.

[pdq]

Every car turns on the compressor to defrost/dehumidify.

[landphil]

Originally Posted by x2xtreme360

Idk how much I like the compressor running practically all the time in the winter. The extra load all the time.

The compressor will not run all the time, it will only cycle on and off when the evaporator core in the heater box is a few degrees above freezing, much like it does when you run the A/C. The difference is, the ambient temperature is much lower, and it takes very little energy to keep the evaporator cold, and when evaporator temps are at freezing and below, the compressor won't run at all. The added load is negligable, and it has no real and noticable effect on fuel milage. I usually run defrost or blend until the windows are clear (if needed), then switch to floor only. The defrost vents still maintain some flow on "floor only" setting, just enough to maintain clear window in most cases.

As mentioned, the side benefit is it keeps the A/C refridgerent oil circulated throughout the system, keeps the compressor seal lubed, etc.