I'm getting conflicting info on this. I going to replace the gasket between the AC unit and the roof (Holidy Ramber MH) some have said to not use any form of sealant when replacing the gasket, and others have said to make sure to use the right sealant. Now, if I am to use a sealant, which one ?

ON a rubber roof.........Dicor.

Bill

I don't believe you are supposed to use any sealant on the air conditioning gasket. At least all the ones I have installed said not to.

The directions say no sealant or caulk. It is a gasket and it does the seal job for you. That's what it is for.

Thanks for the replys ... It's an aluminum roof Bill. One more question, I read somewher to tighten the bolts to 50in. lbs. do y'all use a torque wrench, or just "snug" them up ?

Torque em That way you get the proper compression on the gasket.

I don't know about the torque, but watch your gasket and compress it about halfway. I don't know how yours is set up but also watch the metal around the bolt heads, it shouldn't start to bend. If you compress the gasket too much a lot more vibration and noise is passed along. Too little and you may get a leak.

The gaskets I have installed had a little adhesive on one side from the manufacturer so it will stay in place around the 14" standard opening when you put the top half of the A/C back on. But you still need to place it relatively straight down on the gasket carefully, then a slight adjustment to square will usually be possible. Takes two people at least. On metal roofs it is very important that the area under the gasket be clean, and free of any dents or gouges that might let water through under it.

When I replaced the gasket on my first metal roofed rig, I worked on a sheet of plywood so I didn't accidentally step between the rafters and dent the roof, or cause damage when the A/C was sitting to the side on the plywood. But that was an older floating aluminum roof.

No additional adhesive or sealant necessary.

Here's a good description from one of the folks that do it for a living:
http://bryantrv.com/roofacleaks.html

Thanks for the link RV ...

No prob HJ! Good luck on the replacement job. Make sure when you are done that the intake side of the bottom plenum is sealed from the cold air outlet and they don't mix. There are newer systems that are sealed better and older units that need the barrier between the two adjusted or just plain duct taped to insure the cold air doesn't go back into the warm air intake.

To be honest, all this seems hard to understand until you do it, and then it will not only be clear, but simple when you need to mess with it again. Take your time and it will go smoothly.

I noticed that when I took the grill off. It will need to be resealed , most likely with duct tape.

On the older units HJ the adjustment screws for the metal barrier are sometimes not enough, and duct tape is the only way, and a pain to do in the confined space. Just make sure you completely clean the surfaces of all grease and dirt, and that they are clean and dry from not running the A/C while doing the gasket job, or the condensation while running will cause it to peel off from the natural greases and dirt on the sheet metal surfaces.

But if the barrier has been leaking cold air to the intake side, and you seal it, it will seem like you gained a couple of thousand BTUs of cooling afterwards.

But it sounds like you are already getting a handle on the plenum and the top unit.

One other tip. While you have the top unit off if you need to clean the cooling coils that is the time to do it, but not on the roof. If you clean them while installed the grime drips inside the rig. Clean them on the roof and the cleaner and grime drips down the sides, affecting paint and decals or more. Take it down to the ground and set it on sawhorses and you can spiff it up. Also look for any screw holes in the cooling coil sheet metal shroud, and aluminum tape/duct tape them up so outside air does not get sucked in as well.

If you are going to remove the bottom plenum then take a digital picture of the 12 volt connections under the power box first and mark them. For the top half you only need to power down and remove the 110v pigtail, ( a pain in itself to get a ten year old locking connector to release) but the 12 volt wires can be a bigger pain if you don't have a digital pic as they were, and mark them to be sure.

The electical hookups are simple in this case, remove the cover on the junction box (AC 120V) and remove wire nuts and seperate wires, and the 12 volt conector came apart as it should (nice surprise)... There was some kind of sealer spread on the plenum devider so I will clean it off and reseal. Any advice on what to use for this purpose besides duct tape ?

Hey simple for you, you got it down. My first time I was lucky I could find a wiring diagram because I knocked the 12 volt stuff loose on dealing with the plenum and junction box for the first time, before we had these forums as active. Glad ya got it down pat!

Aluminum or duct tape with cleaned surfaces is my best experience. The foam rubber adhesive junk like for doors just deteriorates after a few years anyway. If they used sealant on the plenum dividers don't. They did that to avoid adjusting the dividers that are adjustable, or to avoid ordering the right height dividers, seen that many times in helping others with theirs when we were on the road. The stock way is an adjustable divider with foam on the top, which was a failed seal from the start. Later systems used adhesive and aluminized fabric which was an improvemnet, but after removal how to reseal?

So sealant can be an option, but subject to the dirt and grease if not cleaned off too. Plus it needs to be the right sealant, not just silicone.

Never used sealant, just duct/aluminum tape and in the new installs just the foam crap that will fail.

They call it duct tape for a reason. It is for air ducts and handlers.

Man that was a fast reply ! Thanks again . You're so right about this forum too !

HJ,
You will pass it along too here on the forums. It is actually fun to help. Better yet to be helped when the experience is there. But the experience is there all over the forums and from many that have the experience besides me.

I am just one of many, including you!

Just pass it on!