Cloth material on AC evaporator box?

[CraigK]

Okay. Another question. In digging around down there on the evaporator box in the engine compartment (actually working on the %@#!*&^%%#! manifold to Y-pipe joint), I noticed what appears to be some sort of cloth or tape on the side of the AC Evap box covering a large hole in the box. As my vehicle is >20 years old, this material is pretty much shot, and I doubt it is acting as a barrier to anything. What is this material for? Why the hole? Can I just use some muffler tape or something to reseal this? Should I have some semi-permeable cloth on this?

As usual, any help appreciated. Thanks.

CraigK

 

[MAKG]

I think it's a heat shield, as it seems to be protecting the plastic evap box from the passenger side exhaust manifold.

 

[CraigK]

MAKG

Yes (thanks), but it seems to be over a large square HOLE! Why doesn't the box have a solid side to it??? Why would it have a heat shield over an open section?

Does it get so hot here that the plastic would melt even with a shield? If so, a cover with heat shield plus isome sort of insulation to keep the absorbed heat from reaching the plastic would be required to replace this rotted and decayed mess?

Has anyone done this?

CraigK

 

[MAKG]

I think your evap box has been "modified."

There is no hole in it, anywhere, that doesn't have something bolted in and completely sealing the hole.

If there is a hole exposing the evap box to the exhaust manifold, I'll bet that A/C doesn't work worth a damn. And it MAY bake the system enough to blow the high side.

 

[RobbieD]

Shouldn't be any unused or empty holes in the evap box. Not seeing it, I'd suggest trying to use a little "shadetree engineering" to fab a peice of plastic or fiberglass glued in place to plug it. The stock "cloth" is an aluminum or mylar foil covered glass fiber insulating blanket, glued to the outside of the box.

 

[MAKG]

Or else a better-condition evap box from the junkyard. But this requires either recovering the refrigerant or pulling the engine on V-6 powered RBVs. There isn't enough room to separate the two halves of the evap box with both the evap and engine installed.

I think at least some later evap boxes will fit an '87. At least, the evap box in my 1991 Exploder sure looks a HECK of a lot like the one in my former '86 Bronco II, except for the addition of a (removable) vacuum reservoir to power the outside-air door.

 

[RobbieD]

Yeah, a replacement box would be the ticket, although it might be a lot of trouble getting if everything is present the donor truck. I managed to get the evaporator and the outside box completely out of my '90 2.9 B2 by pulling the passenger side valve cover and the wheelwell liner. Tight, but doable.

 

[CraigK]

Interesting . . . . (modified box etc.)

The AC system worked reasonably well for two years after a very basic R-12 to R134a home conversion. One thing I noticed was that it would "ice up" requiring shutting down to let it drip and recover more often than I would have liked, even on full internal recirculation mode. Perhaps this was due to excess moisture from outside air reaching the evaporator?

Due to recent damage to the evaporator input line from my shock absorber when my right side coil tower broke in half(!), the AC system needs repair. As soon as I have all the needed parts in-hand, I would like to try and repair both my exhaust manifold to y-pipe leak and the AC line leak at the same time by removing the wheelwell liner for access (thanks for the suggestion - any tricks to this?). I'd very much prefer to not have to remove the evaporator.

I think I can get at least some access to the other side of the evaporator where this "hole" is, perhaps enough to replace the shredded material of the "heat shield", without removal.

CraigK

 

[MAKG]

If the system is discharged, removing the evaporator and box isn't nearly as bad.

Remove the airbox and blower motor (both really easy). Disconnect both evaporator fittings with a pair of wrenches. Remove the accumulator/drier. Then, the box is held to the firewall by four nuts and studs, in a rectangular pattern. These are the ones with nuts over studs, NOT the ones with just bolt-heads showing. The two upper ones are easy to find. The passenger side lower is INSIDE THE CAB, directly below. The driver's side lower is on the firewall like the rest of them, directly below as well (climb under the truck -- with the wheel well removed, this will be easy, though it can be done with it installed -- BTDT). The whole evap assembly will then pull out of the truck. It's fairly tight, but it will go. Assemble the new evap box and the new evaporator (given the damage you described, you NEED that) with the ends still capped in the driveway, and install the complete assembly just like you removed it in reverse.