Square A/C cab v/s non A/C firewall compatibility ?

[tarussell]

I know there are easy enough options/solutions for covering up the hole left behind from going from an A/C equipped cab to a non A/C equipped cab but I am going in the other direction.

I’ve got two ( 85 K-5 & 83 K-30 ) original A/C cabs with all the correct OEM type components but both of the cabs has seen much better days ( and I no longer possess the patience and truly professional skill sets for body work ) but I also can get my hands on a very clean non A/C equipped 1988 R-3500 cab that requires no body work to speak of that I would like to use.

My question is this: is it as simple as carefully cutting a replica hole in the non A/C cab and installing all the components or is there some hidden differences that I don’t know of in each type of cab that makes this a bad plan?
I’ve considered the Vintage Air units but I would like to explore this option before I make up my mind on what to do.

Please advise with pros-n-cons and educate me on cab firewall differences that might be not easily seen.

Thanks, Tom

 

[kennyw]

You will first need to fill the large holes, then cut the smaller holes. Or cut a donor can up for the section you need.

I have have firewall sections from both an AC and non-AC cabs and can get pics tomorrow.

 

[tarussell]

Thanks for the input!

It appears that by going the route of adding the A/C parts to a non A/C firewall that I’ll be mostly cutting since the non A/C firewall only has the blower motor assembly and heater hose holes going through it - that being said I have not studied the inside of the cab under the passenger side dash yet.
Ya bring up a good point of might needing to cut and use/weld in some of the wall of the A/C cabs incase there is a stamped lip or molded or formed ridge in the sheet metal that is needed.

You are a wise man - this is the kind of info and discussion that I am in search of !

Thanks, Tom

 

[83ChevyK5Blazer]

Ill take some pics of the inside tomorrow for ya

 

[nvrenuf]

@tarussell I thought both cabs had 2 holes - 1 round (blower) and 1 rectangular for evap or heater) in addition to heater hose holes.

 

[tarussell]

@tarussell I thought both cabs had 2 holes - 1 round (blower) and 1 rectangular for evap or heater) in addition to heater hose holes.

It could be - I think this is what @kennyw was gett’n at - it’s been so long since I’ve had the nacelle part of the evaporator core area off that I just can’t recall by memory.
Taking a section from the donor cab firewall might definitely be needed if this is to be done.

 

[fourwheelerjeff]

years ago; in 1981 I rolled my first pickup; a 1974. my uncle had a 1976 model sitting in a field. the 74 was ac and automatic. the 76 was non ac and 4 speed. I cut part of the firewall out of the 74 and cut out part of the 76 and siliconed it and pop riveted in place. same with the hump. I cut the floor with the hump and pop riveted the automatic hump in so the carpet would fit correctly.

 

[tarussell]

years ago; in 1981 I rolled my first pickup; a 1974. my uncle had a 1976 model sitting in a field. the 74 was ac and automatic. the 76 was non ac and 4 speed. I cut part of the firewall out of the 74 and cut out part of the 76 and siliconed it and pop riveted in place. same with the hump. I cut the floor with the hump and pop riveted the automatic hump in so the carpet would fit correctly.

I got real lucky on the hump of my R-3500 cab since it is a SM-465 equipped truck and has the raised hump like a K or V series would have.
Planning on swapping over the 83 K-30’s bolt in hump pan while I am dealing with the firewall and A/C parts.

 

[tarussell]

@tarussell I thought both cabs had 2 holes - 1 round (blower) and 1 rectangular for evap or heater) in addition to heater hose holes.

After talking with John I see what he is saying - in addition to the heater hose holes each type has its own blower motor hole and heater core hole ( but in different locations depending on if it was an A/C cab or not ).
John also mentioned that there are some molded/stamped lips on the Inside portion of the firewall on a A/C cab.

The pics coming from @kennyw and Cody tomorrow will help out a lot - thanks fellas !

 

[kennyw]

When the sun comes up, I can get pictures. The holes have formed edges for rigidity. AC vs non-AC put the holes in different areas, different enough that it would be easier to cut sheetmetal from a donor and use as a template or patch panel. Luckily, it would all be covered either way and no patch should be visible.

 

[83ChevyK5Blazer]

Inside and outside

 

[tarussell]

The inside pic really helps !-Appreciate that Cody !

I see the formed lip for rigidity just as @kennyw described and I agree with ya on using a patch panel from one of the donor trucks as being a much better option than just carefully cutting a new hole and patching the other one.

With a little TLC might not even know it ever didn’t come that way and I’ll be sport’n around in style with some COLD AIR blow’n out those vents in the cab !

Appreciate y’all’s input - I feel good about going forward with a solid plan now.
Thanks, Tom

 

[nvrenuf]

Surely the blower hole is in the same location for both applications, don’t you think?

 

[tarussell]

Surely the blower hole is in the same location for both applications, don’t you think?

Yeah it is.
What I didn’t know is that it appears that the heater hose holes are in a different spot from an A/C cab to a non A/C cab.

I figure taking the donor panel from just close enough to the blower motor area ( covering that inlet hole ) and leaving a little extra area around where the evap box attaches should cover all that will be needed and look somewhat OEM in appearance as well when all is said and done.

 

[mark84k5]

I have converted my cab to an ac truck and I will do my best to explain and not over complicate. The blower holes are in the same location but the heater hose holes and the evap coil holes are different. I have all the ac boxes which helped me make a stencile from card board.I started by loosely mounting the new box and getting an idea of where everything goes. In the second pic you can see in the bottom right corner the stencile I used. I basically laid the under hood box on it and traced the out side. Including the screw holes for reference spots. Then did the same with the under dash box.I just got home from work and found the stencil. I put the inside heater box and the outside one on and off several times to check fitment. Couple tips for you. The rectangle hole will need 3/8 pieces of metal to give it rigidity.this was done on both sides of the hole. Stock cans this is all molded in. Second tip: the hole you weld up is on stamp metal which is already under stress. So when you cut it will probably warp just from releasing the stress. And when you go to weld the hole you don’t need this will cause even more warpage.so get your self one of these and put a flange all the way around the new metal before you wel it back in. I wish I did it this way but I butt weld things all the time without issue and ended up spending a lot of time shrinking the metal and messing around with it to get it straight.here is a pic of a peice I made for my fire wall with a flange.
If there is someone on this site that has the knowledge to turn my stencile into a printable file I will send it to them just let me know.
Also I have measurements in pics I will also post from a cab that is an ac truck.

 

[mark84k5]

here here is a bunch of measurements I took from the suburban I got my ac stuff from. Not sure if it will help but here you go.

 

[mark84k5]

You know now that I think of it if someone can’t put it on a shareable file just let me know and I’ll send it to u. If you want it.

 

[tarussell]

@mark84k5 , that is great additional information and thanks for sharing !
Always good to see how different folks go about doing modifications.
I hope this will help others down the line as well as me.

Good stuff and great pics !

 

[kennyw]

Here are pics of the AC firewall. I do not have a complete section from a non-AC version.

 

[tarussell]

Here are pics of the AC firewall. I do not have a complete section from a non-AC version.

View attachment 462249

View attachment 462250

Appreciate the pics !