What sealant should I use between AC gasket and roof?

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.

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)

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.

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.

Golden_HVAC wrote:
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.

Dometic lists an actual torque value when you originally compress the gasket from it's 1" to 1/2" size and that is approximately 40 to 50 inch-lbs so you might use that value to retorque a gasket that is older.

That mumber is from the 6-03 579 installation and operating instructions.

Larry

No sealant required, just proper torque on bolts.

Thanks for the replies.

I just removed my, at least 13 year old and likely 20 year old, Dometic Penguin AC unit. It was held very solidly to the roof with sealant.

I was surprised and disappointed in the extra two hours required to remove the old AC and clean the residual with a scraper and acetone.

Hence my question. I will put the new one on with no sealant!

The Gasket IS the sealant. You do not use any other product. Just the gasket, That is what gaskets do, they seal.

Old-Biscuit wrote:
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)

X1

X2. If you want to do the job right, grab a clicker torque wrench from Harbor Freight, then find the maker's torque recommendations and use those. Hard to go wrong that way.