Aftermarket OR Factory Air

[Twentyover]

I'll take a stab at mikedc's question...

First, I don't KNOW what the flow rate is- it was an estimate based on a subjective feel from bench tests I've been involved in the last couple years. My personal experience with aftermarket has been a no-name in dash G-Body unit and engine compartment S10 from the 80's, VA Gen II Supercooler (never installed) and a Surefit Gen IV in my Camaro. None of these units have air handling components sized similiar to a modern OEM.

Most vehicles of interest to members of this board have relatively steep windshield angles. This permits the use of an engine compartment evap and blower unit and an interior mounted heater core and control doors, and this design is expedient to assemble on these cars in a factory assembly envirornment. This results is the presence of the so-called suitcase on the passenger side firewall.

During this same time, the Japanese were typically using what are now known as lateral flow HVAC units that fit in dash. While air handling components were generously sized, blower motors and registers were frequently undersized and poorly placed or lacked controllability. When American cars started using shallow windshield angles, this general configuration was adopted on some of those models. In time, these systems were also adopted on rwd platforms



If one were to scratch build a system for in dash use, looking at a modern lateral flow designs w/ it's blower motor, heater core, and evap whould be a good starting point. Be creative as far as orientation of the blower motor and heater core- the evap needs consideration to make sure you get good condensate drainage.

Spculating, the reason that aftermarket companies do what they do is because they're not building dedicated units that have a customer specified performance values, in volumes of 250m to 1M units over a couple year run to justify unique design and tooling, along w/ dedicated assembly lines to fit a given model and maximize it's performance. They are building maybe on a good year a couple of percent of that number, so they need to make sure the units fit a large number of vehicles. This is needed to maximize ROI on tooling. To maximize performance wuld require a greater number of configurations, resulting in even higher cost of the unit And we're not even talking about performance measurables like control linearity, register to register and bilevel temperature stratification, control hysteresis, designing air mix chambers to provide consistent temperatures as mode changes.

Tooling ROI forces the manufacturers into physically smaller packages to provide clearance. Every time you shrink a component, you raise the pressure drop through the component, reducing airflow and increasing acoustic impact.

The real reason we don't have what I consider to be OEM quality aftermarket HVAC system? It's not sexy. How often do people oogle the underdash area of your car and marvel at the clean wiring harness, the clever placement of components? I'll wager less often that they check out your brakes or tires. Does it cut your et a tenth, or increase lateral grip? No, owners treat A/C as something they need to do, and they accept limitations either because they believe that's the best they can get, because they don't know any better, or- well, there's as many reasons as there are people. People tend to spend money where it shows.




Responding to the OP's question- my position is, the reason one uses an aftermarket system is because you want a flat firewall or you don't have enough factory parts, or because you want to. If you are not satified with the OEM's performance, find out whay it's not working to your satisfaction before you consign it to the junk heap. If there's inadeqtae airflow, check for flow restrictions in the inlet tract, replace the motor with a more powerful one. If it's OEM duct design is junk (like the Camaros mentioned above), add a face vent or two. If it's not cold enough, make sure the doors seal, make sure the water valve is in place and working.

Unless you want to change.

[John Wright]

Too bad we didn't have dual climate zones in 1970 camaros...LOL

I love that feature on my Silverado, my wife can adjust her side of the truck according to her moods....LOL

[Twentyover]

Components have advanced- but fundamental system design has not. That is, a bypass series reheat used 30 years ago is easily recognized as similiar to a bypass series reheat system today. This is the design generally used by OEM's (and I believe that federal defrost performance requirements demand this type of system to assure compliance within the packaging space.)

There has been advances in heat exchanger design (multiflow condenser, laminated plate evaporators) that increase performance and/or reduce cost, but they perform the same function and are easily recognizable.

Evaporator control have been through a couple iterations, but the fuction it performs (preventing evaporator freeze) is the same. Evap controls have pretty much come full circle-early units used cycling clutch -TXV systems, then both Ford and GM looked at suction throttling valves to keep the compressor engaged full time to eliminate the hesitation felt on clutch engagement. Most are back to CC-TXV or CC-orfice tube systems again to eliminate the fuel economy penalty caused by running the compressor full time.

A real advance, albiet small, in my opinion is the control of airflow. Again, a bowden cable performs the same function as a pulse count or stepper motor, but the ability to separate a mechanical function into discrete steps electrically (unlike vacuum motors, which are on or off, or cables that resist motion after they've been curled around a number of components in routing from the control head to the controlled door) allows for better ATC, dual zone, and some really interesting designs (at least to me).

The second area of small advance, again in my opinion, was the fianl triumph of vent placement and register design requirements over styling considerations. Cars in the 60's and 70's frequently had poorly placed vents (I'll offer up my 70 Camaro as an example- 4 vent locations, 2 low and outboard aiming a driver's and passenger's kneecaps, 2 high and centered, but too small and poor directional control) and poor register design (registers that didn't stay in position after placed and that generated a tumble rather than a jet of air.)

Third was a recognition that air volume was critical to comfort, and upsizing blower motors (and bades and scrolls) to generate higher airflows.


So my answer to the first part of your question is No, there have been no revolutionary advances in A/C of the scale similiar to the difference between say a carb and FI. Each component is easily recognizable, and it's function related to a very silimlar function of of a corresponding cmponent from the 60's.

Regarding the second question, it would be real easy to start a jihad on whether the newer aftermarket stuff is 'better' at cooling than the old stuff. I have an opinion, others have different opinions. Since it's unlikely we will ever see a true objective/subjective A-B comparison, the matter can only remain a opinion. i can offer my opinion temperd by 25 years in auto HVAC- others must provide their own qualifications as to why their opinion has merit.

[mikedc]

Interesting. Thanks for the thorough responses.

Yeah, it's crazy how long it took the factories to start making vent placement into some kind of decent priority. I guess it's a product of the fact that for so long the most common setup being sold on a given car plaform was still the heater/defrost only. Those setups could get away with just a defrost vent on top and blowing the heat out the bottom. The A/C vents would logically grow some increased importance in the minds of the designers as they became the more common setup over the years.

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I wonder how long it's gonna take for them to make the next jump.

I think eventually it's gonna dawn on somebody in the auto industry that there might be some benefit to REMOVING the air from the cabin better. (I'm picturing another blower motor or something to work in the back half of the cabin, pulling some air out of the ceiling & backseat areas, etc.)


Think about it - what really happens when you step into the car on a hot day? Step #1 is that you rush to put down all the windows & get all that greenhouse-heated air evacuated as fast as you can make it happen.

On cold days, you wanna get the cold air out to help heat it up faster, but you don't wanna freeze your nuts off by opening the windows to make it happen.


And that's just the temperature effects. The odor-controlling effects of being able to start pumping air out of the cabin on command would be very nice too. I can't think of how many times I have wished I could do this because of smelly clothes or drive-thru food or something inside the car. You can put the windows down, but if the outside temp is either hotter or colder than ideal then it's annoying. Now you're letting the outside air in too much and ruining the heating/cooling job that the HVAC system is struggling to do.


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[Twentyover]

Vent design really wasn't a consideration until after the advent of flow through bodies (remember Astro-Ventilation?) and power vents were adopted (my first exposure to power vents was early 70's European Fords). After a while, Detroit picked up on a good idea- When my younger brother, whose first car was a 76 Mercury looked at the Camaro- first question after a drive was, there are only FLOOR vents and no Face vents? And I have to turn on the HEATER to get a fan to blow????? Advent of power vents lead to a fundamental change in the way manufacturers looked at fresh air ventilation.

Not really getting why one would add a second blower to extract air- flow through bodies already have relief in body panels to exhaust air added by outside air feeding the blower or ram pressure when the vehhicle is at speed. You have a point on extracting hot air from avehicle, but I would assume that one would use the existing blower at very slow speeds to extract it IF the car know you were coming back in an hour and not a month, to a dead battery. Most systems currently close the recirc dorr to prevent vermin from the outside crawing through the air intake and nesting in the blower wheel , so a secondary path would need to be created.

While this is a reasonable idea, it won't do much to solve the problem, as the specific heat of air is low compared to the specific heat of the hard parts of the interior. Think of it this way- you can stick your ungloved arm into a 450 degree oven and it will feel hot, but that's about it. Grab the pan that cake is cooking in, and you'll feel pain. This is because the specific heat of air is low compared to the pan- the air is hot, but it dosn't take alot of energy to make it hot, so it can't transfer that little energy to your arm and burn your skin. the specific heat of the pan (energy require to raies temperature of a material) is high like that of the meat on your arm.

Where I'm going is, the dash, seat, carpet- all of this is hot too, especially if it's in direct solar, and it will radiate heat and also heat any virgin air, and since it will take alot of air (due to specific heat differences) to being the temp of the interior trim down.

The best way to to address this, IMO, is for the glass to become as close to 100% reflective when the engine is off, so the solar doesn't heat the interior to begine with. Need a science project?


I believe there is flawed assumptions on cold side. Cold air is displaced by the new warm air as the heater core warms up- if you just remove cold air, you are replacing it with new cold air. Unless I'm missing an ssumption here.

And for me.,, i like the fragrance of sweaty gym socks and cold pizza....

[mikedc]

Oh, I wouldn't expect it to change the performance of the system drastically. I'm just thinking it might help speed things up a little, temperature wise.

Maybe it's just me. I also tend to constantly run the A/C in the mode that brings in fresh air rather than recycling the cabin air.




But, the factories put quite a lot of effort into sealing the cabin in every little spot they can. So how does the air get pushed out when the HVAC is bringing in fresh air?

It seems to me that you could put an 8-71 blower onto the intake stage of the engine, but it's still not gonna fill the cylinders very effectively if you've dammed up the exhaust ports too well.

[Twentyover]

Cabins have seals, but are not sealed, or Frank would have died of Carbon Dioxide poisioning. Seals are to prevent air intrusion and noise from undesireable sources, but the cabins have exhaust vents to pemit an air exit path for air coming throuigh the blower.

Look at the door shut face . The exhausters are usually located on the shut face facing the back of the door. On sedans, they frequently exhaust air into the trunk through the package tray, then vent between the exterior skin and the interior trim to the door exhauster. Another alternative I have seen, particularaly on hatchbacks, is through tail light moldings. They frequently have one-way rubber flaps to prevent air from backflowing in when you are in recirc mode.


Personally, I use outside air except when following tar trucks and driving in areas of run over skunks. I've probably had the car on recirc 15 minutes in the last 30 years

[KUL FIR CHICK N]

At this point in the discussion, I feel like I should clarify a few details regarding Vintage Air systems and their features and or limitations relative to early model factory A/C systems. I’ll be discussing Gen 4 systems specifically since they have been mentioned a few times in this thread. The Gen 4 system has several features which differ significantly from any other system available in the aftermarket, so my comments don’t apply universally across the industry.

Since this thread centers around the question of whether to upgrade a factory system or install an aftermarket system, some background is in order. Our founder, Jack Chisenhall, began his foray into the HVAC market on the service and new vehicle A/C system installation side of the industry in the early 1970’s. At that time, many of our beloved muscle cars were still relatively new and their A/C systems were still intact. Many of the systems of that era had issues, lacking both performance and reliability. Some of the expansion and control devices mentioned in this thread (POA, STV) were problematic and led to poor system performance when they were malfunctioning. These valves were complex and were easily clogged by debris circulating through a deteriorating system. Moisture eventually ends up in all A/C systems and when R-12 combines with water, it forms hydrochloric acid. The acid then corrodes the internal surfaces of the entire system. Contamination from ruptured desiccant bags was also a common occurrence. Field repair and or cleaning of the valves proved difficult and unreliable. While the factory A/C systems in some 60’s and 70’s vehicles worked very well, others were very poor performers straight from the factory. Although some (not all) had very generously sized evaporator cores, the system layout was anything but well planned. The air path in a typical muscle car starts out in the cowl, where fresh air is pulled in at the base of the windshield. This air has already been heated slightly by it’s travel across the hot hood, then it is further heated while flowing through the steel duct which shares one or two walls with the engine compartment. From there, it typically runs down into the kick panel area, where there is a valve for fresh/recirculate switching and then into the blower. From the blower, the air is directed into the “suitcase” mounted in the engine compartment. This is where the evaporator is housed. The suitcase shares most of it’s walls with the engine compartment, leading to yet more heat load on the system. From there, the air flows through the firewall, then either through or around the heater core. Finally, after flowing through a series of diverter valves, the cooled/heated air flows out through the in-dash duct work and out through the vents. This long, convoluted, and poorly insulated air path results in a lot of loss, both in terms of air flow and by absorption of heat from the engine compartment. The large evaporator core and other generously sized components gave up much of their performance to these losses. Modern HVAC systems installed in today’s vehicles are vastly superior to those installed in early muscle cars. The basic technology is the same, but a huge amount of refinement has taken place over the last 40 years.

Greg’s recommendation to install a modern compressor and better blower is a good one, but keep in mind that Greg is an automotive HVAC engineer with many years of experience. If one elects to “hop up” their factory system, he should have more than basic knowledge of system design. Otherwise, he may encounter unforeseen headaches he didn’t sign up for.

In contrast, the Gen 4 system is a re-circulated air only system. It is a straight through layout where the air entering the blower is drawn directly from the cabin, then blown straight through the evaporator coil, and then either through or past the heater coil, into a distribution plenum with stepper motor controlled damper doors, and out through flexible duct hose on it’s way to the vents. None of the system has walls shared with the engine compartment, and it only breathes re-circulated air. For this reason, and a few others mentioned later, the components can be sized smaller yet still provide good performance. Gen 4 based systems, both vehicle specific “Sure Fit” systems and the universal “Magnum” evaporator, flow in the neighborhood of 200 SCFM through the vents. For comparison, our Gen 2 Super also flows approximately 200 SCFM and the Gen 2 Compac flows 160 SCFM. I have flow tested several competitors’ units, the best of which flowed 160 SCFM.

Like Greg said, modern vehicles flow in the neighborhood of 250+ SCFM. Many of our muscle cars likely flowed 150-200 SCFM, like the Chevelle Frank mentioned. Third gen Corvettes may be the worst.

Another reason our systems are able to attain high performance with small components is that we run the evaporator at a colder temperature than factory systems typically do. This method allows us to transfer more heat with less air flow. To do this, the evaporator runs at or near the freezing point. The evaporator coil contains a temperature probe that is read by our ECU. The ECU then determines when to cycle the clutch to avoid freeze-up. Most OEM systems use a different approach, controlling evaporator temperature based on suction side pressure. To do this effectively, and to avoid coil freeze-up, the evaporator must be run at a higher temperature. While factory systems usually run 25-28psi on the suction side, our systems can run as low as 10-12psi. To do this, careful placement and monitoring of the temperature probe is required to avoid freezing.

Gen 4 systems use electronic controls rather than push-pull cables or vacuum to actuate the dampers. Some come with potentiometers that attach to the original control panel, eliminating the cables (67-69 Camaro), others come with a complete new control panel (70-78 Camaro, ’68-72 Chevelle). Original cables are often corroded and frozen up and vacuum valves can leak, crack, seize up, or be improperly connected or have missing components.

Factory condensers are often beat-up and leaking from road debris, rocks, bugs, etc. and exhibit corrosion and scale both internally and externally between the tubes and fins. Evaporators are often clogged up by leaves, bugs, mouse nests, etc. and can have leaks that are difficult to repair caused by corrosion. Some evaporators of the 60’s and 70’s even developed leaks within their 1 year vehicle warranty period.

With all that said, if your factory system is in good condition, complete and working, you might as well try extracting the most performance out of it you can. The owner is the best judge of whether his system is acceptable. If it’s not, Vintage Air has a system to fit any vehicle and a fully staffed engineering department working every day to continuously improve our products and develop new ones. It’s a dirty job, building parts for old hot rods, but someone’s gotta do it!

Ryan Zwicker
Director of Engineering
Vintage Air, Inc.

[John Wright]

Lots of good info in this thread...

Thanks to all who added the great info and explanations to this thread.

[CarlC]

Greg and Ryan,

Thank you both for coming into this forum and offering well qualified information on a subject that is not the easist for many of us to grasp. Keeping it civil and on-track is greatly appreciated by those of us who want to learn.