I plugged mine into shore power this morning and let it run till the inside temp was 70 degrees. Probably ran an hour to get there. Then I climbed on the roof and pulled the a/c cowling. I did in fact see condensation on the back of the box that everybody is insulating. That fact alone tells me that insulation in that area might help.
I felt all around the box while the unit was running and it was noticeably cooler right around where the fan mounts and I (not coincidentally) found the condensation. However that was the only place. So, i put some Reflectix in that area only. Basically the whole back side where the fan mounts and nowhere else. I also went ahead and put aluminum tape on all the box seams and put the foam insulation over the low pressure line since I was already up there.
I've also noticed that there is some leakage between the ducts and the ceiling around then vents. In other words, leaking back into the ceiling. So I used aluminum tape to seal up the area between the duck and the ceiling. The vents themselves have a round plastic piece that extends upward and is supposed to seal all that up. They do not seal completely and appear to block some of the airflow too (since some of mine were nearly touching the top of the duct). Two of my ducts had very little air flow coming out (with one of them being in the bedroom
). I snapped the round piece off of the vents and reinstalled them. I can definitely feel an increase in airflow from those two vents now.
It's 91 degrees today with a real feel of 109 degrees right now. My unit is sitting in the full sun and the temp inside is holding steady at 70 degrees. It's even cycled off a time or two. In the past I've had a difficult time holding 70 degrees inside when parked in full sun. It will usually drift up to 74 -75 degrees on days like this.
I'm just going to let it run to see how it does today. I'll report back later.