Heater/evaporator box foam and compatibility

[Jtrux]

My 87 AC box is pretty rough. The AC hasn't worked since before '94 according to the PO and when I got it out, all the foam was garbage.

 

I'm considering taking time to go through with some foam from Home Depot that is used for sealing a window unit to a window sill but it's a good deal of work. Still, if I have to do it, I will.

 

Any other options for foam??

 

Next question.

 

I'm looking at a 95 XJ 4.0/5 speed/4X4 for parts that runs and has working AC. Will that box bolt up to my firewall?

 

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[Minuit]

Oh hey, I'm going through this exact thing right now! I've been agonizing over this for way too long.

 

You'd be very well advised to at least replace all of the gaskets that seal the box from the firewall. Those are a very common source of water leaks which turns into floor rust. On my 91 there's 4. The one around the heater/AC pipes and the one around the drain tube are about 3/4" thick, the blower motor gasket is about 1-1/8" thick (but you could probably get away with using 1" foam) and the one for the fresh air intake is about 1-1/2" thick. They're all made of pretty fine closed cell foam. I scientifically tested them in my sink and they float even when pushed down and absorb very little water.

 

The issue with using hardware store weatherstripping is that I don't know if any of it will be high enough quality to last very long in a truck, at least for the firewall seals. I also don't know if you can get material thick enough, and if you can't you'd have to layer it up which IMO is inviting trouble. I think you would be just fine using it for the other seals in the box since they're not expected to hold water back, just not for the firewall. That's what I plan to do.

 

You can buy all sorts of foam in different thicknesses and sizes here.

 

I'm strongly considering using cross linked polyethylene foam for my firewall seals. Does anyone with actual experience know if XLPE would hold up?

 

Dunno if the 95 heater box will bolt up, sorry.

[cody4359]

sub'd for knowledge since mine is damn near apart right now

 

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[Jtrux]

Oh hey, I'm going through this exact thing right now! I've been agonizing over this for way too long.

 

You'd be very well advised to at least replace all of the gaskets that seal the box from the firewall. Those are a very common source of water leaks which turns into floor rust. On my 91 there's 4. The one around the heater/AC pipes and the one around the drain tube are about 3/4" thick, the blower motor gasket is about 1-1/8" thick (but you could probably get away with using 1" foam) and the one for the fresh air intake is about 1-1/2" thick. They're all made of pretty fine closed cell foam. I scientifically tested them in my sink and they float even when pushed down and absorb very little water.

 

The issue with using hardware store weatherstripping is that I don't know if any of it will be high enough quality to last very long in a truck, at least for the firewall seals. I also don't know if you can get material thick enough, and if you can't you'd have to layer it up which IMO is inviting trouble. I think you would be just fine using it for the other seals in the box since they're not expected to hold water back, just not for the firewall. That's what I plan to do.

 

You can buy all sorts of foam in different thicknesses and sizes here.

 

I'm strongly considering using cross linked polyethylene foam for my firewall seals. Does anyone with actual experience know if XLPE would hold up?

 

Dunno if the 95 heater box will bolt up, sorry.

 

Thanks for the info on foam.  I will keep the forum posted with what I end up doing.

[Keyav8r]

I got some 1" thick neoprene foam rubber from Birmingham Rubber & Gasket and cut a gasket for the heater box at the firewall to replace the one that tore when I pulled the box out. It was closed cell and firm enough to cut with a coping saw. The piece was some scrap they had left over and I got it free (our company buys from them). Check your area for a similar company.

[Airborne Janitor]

Here's where you can get the seal for the heater core while you're in there. I got one from here and it was almost a 100% fit, nothing a quick trim with a box cutter can't handle.

 

https://www.moparpartsgiant.com/parts/mopar-seal-heater-core-tubes~56001322.html?Make=Jeep&Model=Comanche&Year=1989&Submodel=&Filter=(E=ERB;T=DGS)&Location=heater-air-conditioning-housing-core-heater,0000192S,15

[Minuit]

Here's where you can get the seal for the heater core while you're in there. I got one from here and it was almost a 100% fit, nothing a quick trim with a box cutter can't handle.

 

https://www.moparpartsgiant.com/parts/mopar-seal-heater-core-tubes~56001322.html?Make=Jeep&Model=Comanche&Year=1989&Submodel=&Filter=(E=ERB;T=DGS)&Location=heater-air-conditioning-housing-core-heater,0000192S,15

 

Clarification for anyone who reads this later: This is for up to 1990 only. From what I've seen all of the gaskets are long discontinued for us early HO folks :( For 91s and 92s the part numbers for the gaskets are:

56006312 - Evaporator/heater core tubes

56001295 - blower motor housing to firewall

56001196 - fresh air intake, 1991

55035704 - fresh air intake, 1992

 

Some of the gaskets are still available for 97+ XJs as a kit, P/N 4874069AB. I don't know if any of these will fit older heater boxes. Just from comparing them to my 1991 gaskets I really doubt it. I'm not going to be the one to spend $60 to find out.