Is My Indy Right About This??

[Cal Learner]

When I recently had some A/C system repairs (receiver/drier/compressor) done at my usual, reliable indy, he pointed out that my defrost vacuum element needed replacement too because cold air was coming out the defrost with the A/C engaged. I did not do his recommended replacement of the defrost element. However, a couple of weeks later, I had him replace the transmission oil pan/gasket to correct a slow but persistent ATF leak. Immediately thereafter, driving with A/C on, the CCU functioned as it should, with cold air only at the center and side vents, not out the footwell OR defrost vents. For the past month or so since the transmission pan r&r, the CCU has worked perfectly, defrost vents have not let cold air out.

I theorized that the transmission pan leak had affected the CCU vacuum to such an extent that it was leaving the defrost element in its normal open state. Then, when the trans pan work was done, there was no more vacuum leak to affect the climate system so the defrost element functioned as it should by closing those vents with A/C engaged. My indy dismissed my suggestion as impossible. Obviously, I don't know enough about how transmission vacuum and CCU vacuum are related, if at all. What do you think? Is my indy right, as usual?