time for my question of the night... when I turn the defog on does it turn the ac compressor on as well? or does it just pull in outside air and direct it to the windshield vents

 

Yeah the AC comes on to dry the air being blown on the windshield to help clear it.

 

that's what I suspected

 

The compressor doesn't run full time though. You can hear the clutch click on and off if you listen carefully. The A/C takes the humidity out of the air, which defogs the window quicker. During the winter some times I will unplug my compressor to help save some mileage and some wear on the A/C clutch.

 

If it ran full time it would blow up That's why it cycles to stay under like 250 psi.

There's actually a high pressure blow off valve to protect components, but same idea.

 

Compressors don't cycle around here, always on.

 

Seems like the compressor always runs when the AC or defrost are on. The only time I saw the compressor cycling off and on was when it was shot

 

They always cycle unless it's hot as ***** and humid. Like in Florida and Georgia.

The clutch generally cycles every 45 seconds to a minute. If it's cycling fast, like every 10 seconds it's usually because the refrigerant is low.

 

The clutch cycles when the interior temp is about 40 to 45 degrees. This is when the pressure in the system drops below what the sending unit is calibrated at. It will also drop below that pressure if your system is low.