I am installing a Penguin II low profile roof AC unit.What sealant do you recommend to fasten the gasket to the 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

What sealant should I use between AC gasket and roof?

sjholt
Explorer
Sep 29, 2015
If it was mine, I would smear a light coat of RTV on the none sticking surface as additional insurance. I did say if it was mine.
SoundGuy
Explorer
Sep 29, 2015
sjholt wrote:
If it was mine, I would smear a light coat of RTV on the none sticking surface as additional insurance. I did say if it was mine.

It's your rig, you can do anything you want with it but no A/C manufacturer recommends the use of any sealant, just a properly torqued rubber seal affixed to the underside of the top unit. The only "additional insurance" required is periodically checking to make sure those four bolts securing the top unit in place are properly torqued, which I think is the message many in this discussion have been trying to relay to the OP. ;)
Chris_Bryant
Explorer II
Sep 29, 2015
The trouble with using a sealant is that the gaskets are expendable- they will need replacing at some point. If the gasket is sealed to the roof, you've added a huge amount of time to the job- getting the roof clean and smooth.
deandec
Explorer
Sep 30, 2015
Chris Bryant wrote:
The trouble with using a sealant is that the gaskets are expendable- they will need replacing at some point. If the gasket is sealed to the roof, you've added a huge amount of time to the job- getting the roof clean and smooth.

This I learned, but the old gaskets did last 20 years before the refrigerant blew out......

Installed the new AC without sealant although I will not last as long as the old gaskets did.

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What sealant should I use between AC gasket and roof?

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