How hard is it to change the donut seal under rooftop AC?

Are you sure the evaporator drain pan drain holes aren't plugged. A common thing.

Had a slight water leak in my bedroom a/c unit once and pulled the unit up and away from the roof to look at the seal. Sure enough it was crushed flat in one spot and thick everywhere else. Instead of buying the expensive factory seal I picked up a roll of pick up truck cap to bed seal, the roll was about 30 ft long and 3 inches wide for $7.00. I used that to make a new seal for the a/c unit and fixed my little leak. has never leaked again over 6 years.

I've had to replace those seals twice in the past, and it's just as others have said. First see if you can find the leak, check the drain, then tighten the screws/bolts. If you still have a leak, it's not all that difficult to replace the seal, just some grunt work. Best to have someone helping you lift, and have an old mover's blanket or something like it to set the AC on (or a third person so you can put the new seal on while two hold the AC - just be quick!).

IMO with water leaks and Rv's most anything is possible it seems. With a flashlight do you see any discoloring in the foam? Like maybe a part of the foam with a coffee colored stain? Where the foam makes contact with roof is where my leak was and there was some discoloring of the foam. I also found useful was getting a very good look (not just once around) but looking at every inch where foam was discolored. And one of the bolts holes where bolt went thru the bracket had rust on it which also gave me a clue.

Hope others would share some proven short cuts. Took me about a day messing around to get problem fixed.
And after fixing we thought we still had a leak, but turned out to be excess water caught underneath of ceiling paneling and when we park on slight hill a couple of drops would drip on bed. Made us think we still had a problem but turned out water that was caught up there draining when RV at different angles.

If the gasket sealing the AC is the problem, is it possible for it to be leaking into the camper (into the ceiling space between the roof and the inside ceiling) and there be no evidence of water from looking up through the removed filter place from below, inside the camper?

Some new gaskets come with plastic tabs. If so stop tightening when you see plastic tab start to compress. And for a foam rubber gasket, RV places get a lot for them. I think mine was $35.00

But first...take off inside cover, be careful not to break those air flap direction thingies and look with flashlight for where water might be coming inside and getting into roof system or leaking. Then tighten up bolts to same torque, then if still leaking tighten 1/8 of turn. Not a matter of how much you can torque but matter of getting water tight, so be somewhat gentle. When I did mine weight was a mystery to me also. See what model you have and then look on line for your model and see what shipping weight to see how heavy. I just rolled mine on its back and no problems, don't know if I was lucky or not as far breaking cover. But didn't want to lower down or lift back up. I also drew me up a little drawing so when I put elec back I could put it back where it came from.

After you get leak stopped, every year after that (usually pre-season inspection) give those bolts 1/8 turn to keep water tight. Then after many years when gasket no longer has a compressing room left, replace.

Hard to believe a piece of foam is only thing keeping water out. But it does.

Another thing to check is the drain on the pan. Make sure it is clear as if clogged the pan could overflow into the rig.

The roof gasket is 1" thick when new......gets compressed to 1/2" thick when properly installed (4 hold down bolts---torqued to 40 INCH lbs---in other words 'snug')

Snug up the 4 hold down bolts.\\\\\\over tighten will cause other problems ie: distort gasket so it doesn't seal or end up blocking evap cooler drip pan drain holes so condensation ends up getting sucked in and leaks inside RV.

Roof gasket is only thing that should seal A/C unit to roof......no caulking around A/C roof pan.

Hardest part is lifting A/C unit up/out of roof opening and then resetting it back in roof opening.........make sure new gasket is set flat

You can inspect the 14-inch square gasket inside you trailer by removing the ceiling cover and remove the filter. You will see the complete gasket.

There will be four long screws there that sandwich the roof mounted A/C unit with the bottom unit and they are screwed down to depress the gasket maybe slightly less than 1/4-inch. You can tell right away if this is not tight.

These four long screws are the only thing holding the two units together...

Check for proper tightness of the gasket before even thinking about replacement. Might be a simple fix...

I check my A/C gasket on a regular basis... the I59 road in north ALA really gave me fits by bouncing my trailer going over the very rough concrete uneven slabs there..

This is neat pictorial of the A/C unit install.


Roy Ken

On some roof airs, like the Coleman, you can tighten the four bolts. As the seal compresses, the spring tensioners on the bolts try to keep it from leaking.
If you have a Coleman, remove interior unit locate the four bolts. They are 9/16 inch socket size. Tighten them up.
If you plan on replacing seal you would need to provide make and model.
Yes, the units are not the lightest. I was able to roll mine onto heavy card board that was used to protect roof. It would be better with two people to lift unit straight up and over onto cardboard or some other protective material.