Evaporator Question Update 1/31 Got Some Parts

[mikester]

Got a question for you guys but first some info.
I redid the AC box in my wagon. Bought the new seal kit from Mikes Montes. Its been together for quite a while. One day I was looking through some build threads. Texas82GP had some really good photos of the work he did on his AC box. When he was putting it together he used material from an AC filter to wrap the new evaporator. Needless to say I never did this.
I stopped by my friends repair shop today. He was a mechanic at a Buick dealership for years before he opened his own place. He worked for them back in the late 70s-early 80s. When I told him I was taking my AC apart again he said I was nuts. He said over the years he replaced countless evaporators and never used the insulation over. His thought was the condensation would just go to the bottom of the case and drain either way.
What do you guys think ?
Have you guys used insulation or just leave it alone ?

 

[Longroof79]

Mich,
When I replaced my evaporator, I didn't bother putting that filter sheet back on. I think your friend is on the money.

 

[69hurstolds]

Without the filter, it would have the potential to blow condensation that accumulated onto the evaporator coils straight through into the cabin. The evaporator is going to sweat to remove excess humidity which drier, cooler air enters the cabin. Which is what you want. What you don't want is any condensation that could come with it. The "filter" is just a labyrinth to catch and hold any water droplets so they dribble down to the bottom and drain away (as long as your flapper isn't clogged). Kinda like misting a sponge and watching the water dribble out the bottom. It doesn't blow out the other side. Unless you're having a very humid day, it's likely going to drain away. But if you've ever seen the insides of the casing, if it doesn't drain out quick, it's coming in.

Otherwise the water drops have a chance to blow straight on through to the air distribution channels and end up on the carpet. I would say that in NY, it's a different humidity than in the south, so it may never ever be a problem for you without it.

The risk is on the user. Your car, your call. If you don't have a problem with it, then don't worry about it. But if I'm digging into it or replacing an evaporator, it's CHEAP to replace and doesn't hurt being in there at all. Super simple to replace it. Note that it's on the downstream side of the evap. Otherwise it would be useless.

If you ever get clear water on the rug under the center floor outlet when using the A/C and wonder how it's getting there, hint: it's likely not your heater core. If there's an antif-freeze smell to it, then maybe it is.

 

[gnvair]

Not every vehicle has that sheet and to be honest, having some thing laying against the aluminum core just increases the risk of corrosion forming on it and/or dirt accumulations being held against the core. I have replaced a lot of evaporators on a lot of different vehicles by a lot of different manufacturers. Many do not have anything over the core. I would not lose a moment's sleep over not having it.

 

[69hurstolds]

While I'm on board with the idea that there's a very small chance it would be an issue, it's never a problem leaving it out until you have water in the car.

Your not working for rate on your own car. If you are doing a restoration for yourself and you still have a filter on your old evap, I recommend you put it back in replacing the deteriorated one with a new piece of similar foam material, don't be lazy and cut corners. It's not like you're going to lose any air flow unless you mess up and use closed cell foam. But if someone has already beat you to it and threw the clips and mounting pins away, you can't fix what isn't there.

And the chances increase when you start doing things to increase air flow like different fans or faster motors, etc. My best guess is, GM did it to "fix" a poorly designed G-body ducting/drain system because they were getting warrantee issues with wet carpets during A/C season.

If your system is original, you're probably losing air flow through all the crumbling foam gaskets anyway so you wouldn't push enough air through the evaporator to blow water in as it is.

My original shiit's been in there for over 30 years and the evap's not corroded yet. I've never seen or heard of an evap failure due to the filter sheet. I find that people tend to leave stuff out when they really don't understand why something is there to begin with. If you don't want to do it right, that's your call.

 

[TURNA]

Leave it alone

 

[81cutlass]

My wagon is an 80 and when I turn right with the AC on if it's humid it drips condensation onto the carpet. I don't know if it has the foam or not. The drain is clear.

My 81 Cutlass has the foam and I've never had it drip inside.

 

[Longroof79]

The question is, why doesn't the manufacturers include the foam sheet? To cut down on the total cost per unit? ....or is it just left up to the owners discretion?

 

[TURNA]

How often will you be actually using it?

All it does is rain here in the summer

 

[69hurstolds]

The question is, why doesn't the manufacturers include the foam sheet? To cut down on the total cost per unit? ....or is it just left up to the owners discretion?

GM included the foam sheet and it's held on with clips and pins. It actually added cost per unit. As to when they started doing it, I don't know. Aftermarket suppliers don't even care so you won't see them. They sometimes can't even make an evap unit fit correctly with the tubing, as seen in the video below.

oldsofb , aka Hutch, rebuilt his HVAC unit and did a remarkable job. Here's a vidcap of the filter that came on the car. On the left there's a couple of wire clips to hold it at the bottom and the downstream side just has push in clips.

Here's the video when he's doing the foam seals.