A/C Cycles on other settings than A/C?

I have a 1990 Dodge D-150 5.2l and recently I finished repairing the A/C system back to stock (Including a new charge of the R-12 refrigerant, hard to obtain). The system had not been run in well over a year since one of the hoses had formed failed at the crimp seal. This was repaired recently and we finally got the A/C running again.

However, last night, I switched on my Defrost option on my system and the A/C pump started cycling like I was using the A/C. I thought this odd and switched it over to Vent. It cycled there. I didn't try heat, but, after sitting for the night the A/C system didn't cycle except for when I turned on the Defrost again. Heat and Vent didn't cause it to cycle. I'm truely stumped as to what might be causing this.

this is normal all a/c systems cycle on defrost mode
eaven if a/c switch is not depressed

Yes, I belive that it will run in short cycles during def or mix because it has an air dryer that removes the moisture as to not fog up the windshield. That is what I have understood from the people I have talked to.

this is normal all a/c systems cycle on defrost mode
eaven if a/c switch is not depressed

That is true it does so, so that the clutch does not freeze up during long periods of nonuse like winter. :thumbsup: