What sealant should I use between AC gasket and roof?

I worked on the emergency vehicles at my work with rooftop A/C units that where leaking. The gasket had compressed itself while it was parked, and now the bolts where loose. Like I could turn them 3 turns before they made contact with the inside frame of the A/C/ Then I tightened with a nut driver.

You can use a socket wrench and extension to make it easy for you, but do not "Tighten" beyond finger tight and about 2-3 more turns. Then check it again in a month or so, and snug it down a bit more if required. After 2 years, check it again.

The bolt is probably a 3/8" X 18 threads per inch. So each turn is 1/18" compression on the gasket. 2 turns = about 1/8".

Good luck,

Fred.

To the best of my knowledge, gravity is all that is required to attach it to the roof...assisted slightly by the mounting bolts. The gasket is the seal. It would be nice if all the other things that go through the roof were as straightforward to seal properly.

NOTHING!!

Clean roof area around opening, Clean A/C Unit pan where old gasket was.

Install new gasket and set A/C Unit.

Tighten the 4 hold down bolts finger tight in cross pattern.
Then slowly 'snug' them up until gasket has been compressed by half (1" thick compressed to 1/2")
DO NOT OVER TIGHTEN.........just hand snug (Can crush gasket, warp roof and/or A/C Pan and cause leaks)

The new gasket will have one side that is peel and stick. It sticks onto the ac unit. At least the 2 that I have worked on were like that.