70 chevy A/C ?'s

[jjzepplin]

So I am getting ready to get the a/c going and realized that the recirculated air comes from the vent inside the cabin. Almost the entire vent system has no insulation whatsoever. It looks as if the air would get heated from the outside heat beating on the sheet metal. Any one notice this? I was thinking of insulating this area and possibly making an air cabin type filter for this vent. Any ideas?

[jjzepplin]

OK.. Sooo I've come up with a radical idea. (I am nuts) I am going to close off the cowl to "fresh" air. I am sick of leaves and trash rotting in there and getting into my evaporator and heater core.(as well as rusting out my truck) I am going to drill out the sheet metal right in front of the fan squirrel cage and go straight thru to the cabin. I should be able to duct this easily and install a round engine type filter. The kind used for fuel injection rice burners. I will the use the vents for some speakers. If I need fresh air I will just open a window. THOUGHTS????

This should eliminate the heating of the duct from the outside air. I realize the outside air will not be able to enter my cab except through a window but I never use that option anyway.

I am thinking some removable aluminum plates over the holes in the cowl so I could still work on the wipers if necessary.

[jjzepplin]

Did I do something wrong or does any one know what I am talking about? Maybe I need to post a pic. The part I want to cut out is just inside the hole for the fan.

[jjzepplin]

Bumping this thread cuz I am going to get to cutting this thing out soon if there are no objections..Someone say don't do it ?? I may end up with the best a/c ever..or make a big mistake.

[El Campo]

I too have thought about stuff like this. I was thinking of eliminating the outside vent and removing the door off of the inside kick panel. Another suggestion I got on here was to put some radiant barrier on the evaporator core box to keep radiant heat from the engine away.
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[67c10rustbuket]

Originally Posted by jjzepplin

OK.. Sooo I've come up with a radical idea. (I am nuts) I am going to close off the cowl to "fresh" air. I am sick of leaves and trash rotting in there and getting into my evaporator and heater core.(as well as rusting out my truck) I am going to drill out the sheet metal right in front of the fan squirrel cage and go straight thru to the cabin. I should be able to duct this easily and install a round engine type filter. The kind used for fuel injection rice burners. I will the use the vents for some speakers. If I need fresh air I will just open a window. THOUGHTS????

This should eliminate the heating of the duct from the outside air. I realize the outside air will not be able to enter my cab except through a window but I never use that option anyway.

I am thinking some removable aluminum plates over the holes in the cowl so I could still work on the wipers if necessary.

EXACTLY my thought on the cowl. Sounds like a plan to me! I personally use max/recirculate at all times in all my vehicles so why would I want to introduce fresh hot air in, right. Crack a window if you get too cold

[Katrina/10]

Why not just block the cowl flapper closed, and the kick panel vent open? No need to modify anything else.

[leddzepp]

Originally Posted by Katrina/10

Why not just block the cowl flapper closed, and the kick panel vent open? No need to modify anything else.

Agree.

[jjzepplin]

Originally Posted by Katrina/10

Why not just block the cowl flapper closed, and the kick panel vent open? No need to modify anything else.

This is because the air would still have to go through the engine-heated cowl section behind the fender through the vent system. If I go straight through to the cabin by opening up the sheet-metal in front of the squirrel cage It would eliminate that heating of the air.

[Katrina/10]

Originally Posted by jjzepplin

This is because the air would still have to go through the engine-heated cowl section behind the fender through the vent system. If I go straight through to the cabin by opening up the sheet-metal in front of the squirrel cage It would eliminate that heating of the air.

I see, that might work.

[jjzepplin]

Think I'm gonna do it! Tell you how it goes when I get it Blowing. I think the lack of resistance should work well too as well as keeping junk out of the evaporator. Might put a k-n filter in later but will try this for now.

[leddzepp]

Originally Posted by jjzepplin

This is because the air would still have to go through the engine-heated cowl section behind the fender through the vent system. If I go straight through to the cabin by opening up the sheet-metal in front of the squirrel cage It would eliminate that heating of the air.

If you have a factory system that is functional and operates as it should, the A/C will freeze you out of the cab even on the hottest days. It sounds as though you are dead set on trying this idea though, so go for it

[SS Tim]

Originally Posted by jjzepplin

Think I'm gonna do it! Tell you how it goes when I get it Blowing. I think the lack of resistance should work well too...

Trying not to mess up a good theory with bothersome facts. But... If you are using recirculation all the time it is inviting rust and moisture collection. Use recirc. to pre-cool then shift it over to nomal for best overal A/C performance. Keeping the evaporator clean and draining are the best improvements you could do. A thermal barrier from engine heat on the outside of the case and the engine side of the firewall and cab floor may help but not necessarily cost effective. Worring about convection from the sheetmetal is pretty far down on the list though, but white roofs do help. Your glass area is the biggest problem overall. You would be amazed seeing an A/C thermal preformance map. If you move the air through the system too fast it will not cool as nearly much. Many GM vehicles actually cool better on a medium vs a high fan setting for this very reason.

[jjzepplin]

Originally Posted by SS Tim

Trying not to mess up a good theory with bothersome facts. But... If you are using recirculation all the time it is inviting rust and moisture collection. Use recirc. to pre-cool then shift it over to nomal for best overal A/C performance. Keeping the evaporator clean and draining are the best improvements you could do. A thermal barrier from engine heat on the outside of the case and the engine side of the firewall and cab floor may help but not necessarily cost effective. Worring about convection from the sheetmetal is pretty far down on the list though, but white roofs do help. Your glass area is the biggest problem overall. You would be amazed seeing an A/C thermal preformance map. If you move the air through the system too fast it will not cool as nearly much. Many GM vehicles actually cool better on a medium vs a high fan setting for this very reason.

I understand what your saying. The evaporator should be doing just that"evaporating" any moisture. It gets pretty moist here in Florida and pretty darn hot too. I am looking for a more efficient system for a low dollar amount. Your home a/c is a direct recirculation system and most new cars are the same as well. Why not my old truck. I'm thinking cause it was 1970 and they were not that advanced then. So if it does work my a/c should freeze me out on low fan settings and shut off my cycle saving me gas just like my home system...You make a good point with the glass as well so some tint is now in the mix. If it does not work I will just tack a piece of metal back in.

[Andy4639]

I can't see the sheet metal warming the air back up once it is cooled down. That is the whole idea behind AC systems. Once the truck is working and it's cooled off it should stay close to that temp if the system is operating like it should.
I blocked off the cowl vent last summer on mine and leave the passenger side vent open and it runs 35-40 degree's no matter what the outside temp is.
Yes insulating would help some also and having the AC blow straight through to the cab may work fine. I can only see the noise level going up though because of the fan being straight to the cab plus the engine noise may be more. The only thing to do is try it and see! Good luck and post what you find.

[jjzepplin]

Doing it this week and will let you know. Any one got a good way of cutting that sheet metal? I usually drill a series of small holes and then use a high speed cutting tool with a drill bit that has teeth on the side for elongating holes to cut through what's left and then de-burr with a rotary type file of sorts but it's a lot of work.

[Katrina/10]

A high speed air reciprocating saw works great.

[jjzepplin]

I don't have one of those saws so here we go old school. Doing it tomorrow I thinks. I just have to get that beast on the road. Are you with me?

[So.Cal.Super]

Originally Posted by jjzepplin

I understand what your saying. The evaporator should be doing just that"evaporating" any moisture. It gets pretty moist here in Florida and pretty darn hot too. I am looking for a more efficient system for a low dollar amount. Your home a/c is a direct recirculation system and most new cars are the same as well. Why not my old truck. I'm thinking cause it was 1970 and they were not that advanced then. So if it does work my a/c should freeze me out on low fan settings and shut off my cycle saving me gas just like my home system...You make a good point with the glass as well so some tint is now in the mix. If it does not work I will just tack a piece of metal back in.

The Evaporator Does not in theory evaporate moisture. As Cold liquid refrigerant is fed through the heat exchanger the warm air blown across it boils the liquid returning it to a gas state (evaporates) and sends it back to the compressor to be cooled and turned back into liquid. The coil maintains a temp low enough to cool the air moving across it while maintaining a temp split based on design. The by product is it removes the water from the air as it passes over the coils (due to the temp being so much lower then the air ) and expels it from the box. The colder you can get the coil the more efficient you can cool the air and remove the humidity from the air crossing over it. Higher fan speeds increase your cfm and cool less efficient as Tim stated. You can't lower the coil temp anymore then 34f or you start to make ice. An iced up coil produces nothing for air flow and therefor you do not have A/C.
Your home A/C is only a direct recirculation system because in theory you will introduce fresh air into the home through doors opening and closing, etc.
In a commercial application you need to maintain a 15% fresh air introduction
I have not seen a new vehicle yet that has eliminated the fresh air introduction. We had problems with our 2006 sequoia after a road trip from CA to south FL and back. The system was set from the factory for max a/c (recirculation) every time it was turned on. The evap never dried out because of the lack of fresh air the system mildewed. We fought them and had them replace it under warranty because there was no ozone safe, enviro friendly flush here in CA. (there was in Florida, the dealer offered it but we didn't have a problem till we got back.)
As far as new home systems go, you have to remember, better insulation, dual pane windows, and more energy efficient systems (do to lighter thinner metals in equipment construction) are what help your house. When it reaches set point it shuts off. Put that same system in a 1970's house and it will run just as long. I have 3 machine at work side by side, 1 Trane energy efficient variable speed, variable drive chiller that uses new gas, lighter metals etc. and 2 1967 carrier Cast iron r-11 (not r-12) 4160 voltage tanks. Energy efficient… not a chance, cooling efficiency… Those carriers will cool twice as fast as that Trane, then idle down and bake the seals out of themselves because they want a heat load to work with and 40 years of remodeling, and upgrading has removed it. Don't knock old tech.
Tint your windows and insulate your cab would be my recommendation.
In the end it's your truck and you can do with it as you want. I do really hope it does what you want. I just hate to see you cause yourself a problem in another area because of it.

Let us know how it works.

[jjzepplin]

Originally Posted by So.Cal.Super

The Evaporator Does not in theory evaporate moisture. As Cold liquid refrigerant is fed through the heat exchanger the warm air blown across it boils the liquid returning it to a gas state (evaporates) and sends it back to the compressor to be cooled and turned back into liquid. The coil maintains a temp low enough to cool the air moving across it while maintaining a temp split based on design. The by product is it removes the water from the air as it passes over the coils (due to the temp being so much lower then the air ) and expels it from the box. The colder you can get the coil the more efficient you can cool the air and remove the humidity from the air crossing over it. Higher fan speeds increase your cfm and cool less efficient as Tim stated. You can't lower the coil temp anymore then 34f or you start to make ice. An iced up coil produces nothing for air flow and therefor you do not have A/C.
Your home A/C is only a direct recirculation system because in theory you will introduce fresh air into the home through doors opening and closing, etc.
In a commercial application you need to maintain a 15% fresh air introduction
I have not seen a new vehicle yet that has eliminated the fresh air introduction. We had problems with our 2006 sequoia after a road trip from CA to south FL and back. The system was set from the factory for max a/c (recirculation) every time it was turned on. The evap never dried out because of the lack of fresh air the system mildewed. We fought them and had them replace it under warranty because there was no ozone safe, enviro friendly flush here in CA. (there was in Florida, the dealer offered it but we didn't have a problem till we got back.)
As far as new home systems go, you have to remember, better insulation, dual pane windows, and more energy efficient systems (do to lighter thinner metals in equipment construction) are what help your house. When it reaches set point it shuts off. Put that same system in a 1970's house and it will run just as long. I have 3 machine at work side by side, 1 Trane energy efficient variable speed, variable drive chiller that uses new gas, lighter metals etc. and 2 1967 carrier Cast iron r-11 (not r-12) 4160 voltage tanks. Energy efficient… not a chance, cooling efficiency… Those carriers will cool twice as fast as that Trane, then idle down and bake the seals out of themselves because they want a heat load to work with and 40 years of remodeling, and upgrading has removed it. Don't knock old tech.
Tint your windows and insulate your cab would be my recommendation.
In the end it's your truck and you can do with it as you want. I do really hope it does what you want. I just hate to see you cause yourself a problem in another area because of it.

Let us know how it works.

I think you are right. The evaporator does not evaporate moisture, it rather collects and drains it out of the box. That is why we always get a/c puddles under our cars. I don't think I'm knocking old tech in fact I would like to use r-12 when I charge the system. Since I am not increasing the speed of the fan I don't think this would be an issue either. My thought is to make the system more efficient by working less to get the air cold. When I cut this spot out it should be colder air going into the system thereby making it easier to cool. Like pouring cold water onto ice -less work to make the water colder-easier than pouring warm water on ice. This truck cab will in no way be "air-tight" and never will be. In fact it will probably leak like crazy through small holes, warped doors, old pile seals and rust thru. I do understand a/c functions as my wife and I installed our own central air in my home and have the gauges and a 30lb r-22 tank to top off the unit if ever needed. I ran all the ducting and did the air calc as well. Don't worry, I got a permit and passed building codes. So I am thinking since my home a/c works so good- it cannot hurt to make some minor modifications to my 42 year old truck system. After all, if we did not try change we wouldn't have a/c to start with. I think all of these suggestions are very good and I appreciate all the responses. This truck should be very cool when I am done. I plan on insulation, tint, and shivers. I won't be driving it to Cali any time soon but may go back there someday.(spent my first thirty years in Alameda County) I drove my 72 Blazer out here in 02 with no a/c. This truck never had a/c so she will be shocked either way. I have seen some really cool modifications on these trucks but never this one. Since I am cutting holes in the firewall and dash one more couldn't hurt right? Sorry for the lengthy response....

[jjzepplin]

The main idea for this is to not use the cowl for air and to close it off. My Blazer has sustained severe rust from the Florida leaves and rain getting in there and every time you get on the road leaves and trash blow into your eyes and it can be somewhat dangerous. There has to be a better way. I would like to shave the entire cowl as well. I saw it done on here not too long ago.

[jjzepplin]

Originally Posted by Katrina/10

Why not just block the cowl flapper closed, and the kick panel vent open? No need to modify anything else.

Well I went out there today and looked inside the cowl. I have a great seal on the flapper cause there was a big a$$ puddle in there just sitting and waiting fro some rust to occur. I t may be the way I have the truck on jackstands but I think I will eliminate that flapper and close off the cowl section with aluminum plates.
Oh and I did cut that hole in the firewall.
Raining like he!! right now so I will post some pics later.