Do or don't
 

I got AC off on bench now....The Roof is alu and all seams Eternabond taped//and 3 coats Kool seal every place except under AC back when this was done..Well??? be....Would it be good to Tape around the 14" AC hole with eternabond tape or leave the Painted alu just clean (that area is really in good shape)..and then set the AC with new gasket....Of course Kool sealing whatever did not get done under body of AC back when AC was mounted...Not the gasket sealing surface..?????

Sorry sometimes its hard to explain on paper for me!!!hope it comes across

Big "O", just ensure the area where the gasket sits is clean! You really don't need to do anything else. When installed right, the seal does the job. READ the install instructions carefully. Some gasket companies call for a 1/2' compression, while other companies call for 3/4' compression of the seal. The compression is done with those long mounting bolts. Snug them down after the unit is centered. Then, (I used a popsicle stick with a mark around it) tighten in a cross pattern until you reach the desired compression.
Tree

I want to emphasize one point Tree made in his excellent advice to you, cva. Anytime you tighten anything down over a gasket, make sure you tighten each bolt or screw around the perimeter in a CROSSWISE pattern a bit at a time (possibly a half turn) so that the thing you are mounting settles "evenly" onto the gasket.

This also applies to other things as well (as you might know) such as mounting tire rims on vehicles or your trailer.

Sorry if I'm telling you something you might feel is obvious. I'm doing this for anyone who might not understand the critical importance of how to mount such items. I know there are several members on the forum that are new to such mechanical concepts.

- Jack

Thx Tree and J and J...any reminder is always good...esp on tighting (torque) sequence and clean..Thats all second nature to me...Rebuilt many Motors ..

I was thinking eternabond might seal against new gasket better than that dimply surface of the painted alum.. I always want anything I do to last forever..and i don't like leaks.

and even less DO OVERS..

Note that gasket installation instructions for A/C units warn against using any kind of sealant. You could make future removal of the unit a nightmare.