Drip Pan for Heater Core and A/C removed - next steps - type of silicone?

I've been reading many informative posts, here and on other forums, about fixing the seal on the box holding the heater core and A/C condenser on my 1991 OCC.

I've got the drip pan off (what a pain) and am preparing to seal it using silicone, but I wanted to know what kind to use?

I saw where Fred Kiehl used black silicone, but was it RTV or just your run of the mill all-purpose silicone?

Does it really make any difference?

I'm frankly stumped as to why the A/C was leaking into the passenger side and getting the carpet wet.  The drain was not clogged and I had a 90 degree drip tube installed on the engine side of the firewall.  There were no leaves or debris in the pan when I removed it either.  I'm guessing that simply having a bad seal on the pan was enough.

I've gone thru a dry run of reinstalling the pan without any silicone, so I hope that goes smoothly.

I just need to know what kind of silicone should be used.  

Also, Fred, you mentioned putting silicone on the "left front screw hole that goes to the post".

Which one are you referring to in the picture below?

Many thanks in advance.

Well, I went ahead and used GE Silicone II, due to its ability to handle moisture/water after 30 minutes of cure time. Keeping my fingers crossed.

Would still like to know which screw needs coating with the silicone. Maybe I'll do all of 'em!

mtennant wrote:

I've been reading many informative posts, here and on other forums, about fixing the seal on the box holding the heater core and A/C condenser on my 1991 OCC.

I've got the drip pan off (what a pain) and am preparing to seal it using silicone, but I wanted to know what kind to use?

I saw where Fred Kiehl used black silicone, but was it RTV or just your run of the mill all-purpose silicone?

Does it really make any difference?

I'm frankly stumped as to why the A/C was leaking into the passenger side and getting the carpet wet.  The drain was not clogged and I had a 90 degree drip tube installed on the engine side of the firewall.  There were no leaves or debris in the pan when I removed it either.  I'm guessing that simply having a bad seal on the pan was enough.

I've gone thru a dry run of reinstalling the pan without any silicone, so I hope that goes smoothly.

I just need to know what kind of silicone should be used.  

Also, Fred, you mentioned putting silicone on the "left front screw hole that goes to the post".

Which one are you referring to in the picture below?

Many thanks in advance.

A. almost all silicone is RTV (room temperature vulcanizing). I used the black, because I had some left over from an intake manifold installation. Fill the channel with a bead and assemble immediately. Do not forget to fill the channel between the two chambers.

B. Thanks for numbering or lettering the yellow circles (you did not give me any way to designate the one you are concerned about). The one that needs some silicone is the only one that goes through the pan tray itself.

Your leak may not be the drip tray. It may be the front windshield along the bottom on the passenger's side. I had my windshield separate from the body in that area. I made a retaining dam from modeling clay to hold water at the windshield along the edge. I made it into 3 separate segments, and filled them with water. The center one drained (the water went into the passenger's side footwell), and the others held water. Leak found.

Thanks Fred. Your information found elsewhere and here was invaluable.

I've confirmed that the seal was leaking on the pan, as I could see the water seeping out on close inspection. Also, I took a long trip this weekend with the AC on. There was no rain, but a towel I stuffed up against the drain area of the firewall inside the car got very, very wet.

I haven't ruled out the windshield as a secondary source. One thing at a time.

I'm still confused about the screw you recommend sealing, but if this works, I'll simply do them all.

I'm going to let the new gasket cure overnight and test it in the morning.

Thanks again for your detailed information that is valuable to many, including me.

Ran the AC today and did not notice any leaks. Plus it rained today and no evidence of leaks from that either. Will keep my eye on the floor and check for moisture.

Will go back and seal the screws later.

Thanks again!

If it does not leak, you do not have to seal the other screws. Save yourself some work.