A few general vintage Ac questions before purchase

[yellow1098Greg]

Just got a couple questions before I spend the money iv been saving for a vintage AC system in my 77ta. I know based on reading that this system is the best possible option for cold modern AC in a classic muscle car. But I was wondering how does the system compare to systems in todays cars? For example in my vw passat even in dead summer in florida it gets to cold to leave it on high, it will freeze you out. All newer modern cars are like this. Will I get the same kind of performance from the vintage system? Obviously insulation etc. plays a big role in this as well which I will work on at the same time I install the system. But please give me some feedback on that. Also when the system is installed does the motor have to come out of the car? Hopefully I can get my car to be a comfortable ride I can use without ruining my shirts. I want it ice cold. Thanks for all the info and insight.

[dontlifttoshift]

On Gen IV units we routinely get 34 to 38 degrees out of the vents.

We recently did a Magnum (universal GENIV) install in a 51 merc. Car was painted but had no weatherstripping, insulation, sound deadener, or interior. he took the car to to Salinas Kansas for the KKOA show and cruised the fairgrounds with the windows down and it stayed cool inside the car. It was over 100 degrees that weekend. I didn't witness this, but the customer did call to relay that story and say he was happy.

You do not have to remove the engine.

[Twentyover]

There are several components involved in determining A/C comfort. Airflow volume, directional control, sound levels, and outlet temperature.

Modern cars flow 250-300 cfm (usually outside air measured with the inlet plenum pressure drop, blowing into a sealed body with zero body or specified pressure.) I don't believe any of the aftermarket A/C suppliers publish airflow volumes (I've never seen it), and have not objectively measured the Gen IV in my 70 Camaro. I speculate, based on airflow 'feel' (perceived volume based on outlet velocities) the system delivers no more than 140-160 cfm. Totally subjective estimate, I'd encourage the aftermarket to publish information. This is a full recirc system, so doesn't suffer the aiflow reduction an inlet plenum pressure drop causes.

Directional control is one of the most underrated features of OEM or aftermarket A/C. Outlet air temp is meaningless unless you have some of that blowing on you. For instance, the aforementioned 70 Camaro had 1 outlet located at the bottom of the IP by my left knee; two centrally located at face level, and a fourth chillin' the passenger's right knee. I deactivated the driver's knee vent, added a face level vent covering the headlight and wiper switch locations (these were relocated to the lower IP,) and am considering adding a second face level on the right side of the gauge cluster. This would provide 4 face level vents and 1 knee cooler vent for the passenger. More vent area = reduced system pressure drop = more air flow- a bonus. I'd move the passenger knee cooler up to face level if there was an easy way to do it. Automotive OEMS have established target locations and velocities their systems need to meet.

Sound pressures are a wild card. If a system is too loud, you'll pull back fan speed. Lower airflow, lower heat transfer. Have seen noisy outlets drive thermal performance complaints.

Finally, for the sake of this conversation, in my opinion is outlet temperature. Vintage air runs a lower than OEM typical suction pressure to lower evaporator temps. Most OEMS will run suction pressures that yield a 29-34 degree evap temp, and will frequent cycle at temperatures higher than that as a strategy to prevent evap freeze. Vintage air (and I assume other aftermarket manufacturers) take a technically riskier strategy of plunging evap temp below freezing to yield greater thermal performance from a smaller package sizes. This is not a flaw, it is a design consideration and decision. By running full recirc systems, and with a well selected temp sensor location, I speculate the high risk strategy pays off because because you rarely encounter a car carrying enough people perspiring and aspirating enough moisture that it overtakes the system. The risk pays off. It would be interesting to test an aftermarket system with a large solar load in an OEM freeze test. You would need to put a couple fat sweaty guys in the car to get a humidity load, which the OEM does by controlling the environment in his wind tunnel.

As to which makes more 'cold', heat transfer is the change in heat content per unit of air x the amount of air. There's latent (humidity change) and sensible (temperature change) components involved. Any assessment of heat transfer needs way more information than is published. I have an opinion, but I can't support it with data.

In my opinion, the most significant weakness of the aftermarket A/C systems I've had occurs in mid ambient conditions. In an oem system today, the evaporator runs a full blast, cooling the air as much as possible. If that's too cold, a fraction of the air is routed to the heater core for reheat, with the heater core running WFO, and that air is blended with the full cold air, yielding a consistent air temperature. Compressor will only cycle off as a part of the freeze protection strategy.

Some aftermarket systems (and Vintage Air exhibits this condition, so I assume it is part of the control strategy) will cycle the compressor to modulate evaporator outlet temperature when less than 100% cooling is demanded prior to starting reheat. Practically, this results in perceptible outlet temperature swings from full cold the whatever the control strategy tells the compressor to cycle on. People have varying sensitivity to this- My brother has no idea what I'm talking about, while it drives me up a wall after the sun goes down and I'm running with just moderate cooling.

I personally do not believe a Gen IV performs as well as a modern OEM- But you haven't defined performance, and there's inadequate published information to make an objective comparison. There are also a number of variable after the HVAC unit that impact performance. I have a Gen IV in the Camaro, so do have a basis of comparison. My next project will have factory air handling components.

Is the Gen IV a flawed system? No, it clearly meets the requirements of a huge number of people, in every area of the country. It's designed to a set of packaging and assembly requirements different than an OEM. That different design brief yields a system that differs from OEM's. I've spent a few years with my butt planted in a passenger chair whining about stuff that most people don't notice. I've got some likes and dislikes, and have strongly held opinions.

I'm also dislike some directions the OEM A/C systems are taking to meet CO2 requirements, but I understand why they're happening.

Anyway, long boring post is over.

[Fras]

Wow, you know your stuff when it comes to AC!! My Gen Iv chills me in the AZ heat pretty damn well.

[yellow1098Greg]

Well twenty thank you for explaining in depth the differences and how they work. I surprisingly enough grasped quite a bit of the concepts you were getting at. How will you incorporate those factory handling components into your next project to improve your system?

And Donny and fras..... Thanks for your input as well. That feedback is also extremely valuable.

[Twentyover]

First, I want to emphasize that I was answering a question "how does the (Vintage Air) system compare to systems in todays cars?" I did not attempt to respond to the question "Will I get the same kind of performance from the vintage system?" because, as I indicated, 1098 did not identify he meant by performance.

I have nothing but praise for Vintage air- they produce an excellent product that serves the needs of many people. They have a different set of design criteria than an OEM and, their product meets the needs and expectations of many customers. Including keeping people like Fras cool in hot climates.

That said, couple examples of ideas- Not sure I'll use in my next projects but I will consider all and make decision based on time/cost/etc:

Face level vents with good directional control. I've had good experience using rectangular barrel vents from cars like mid 70's to late 80's GM products. There are probably many others out there that work equally well. I prefer those outlets with a vertical pivot axis and horizontal vanes. Couple examples of ideas:
http://allusedtruckparts.com/item.php?item_id=377
http://www.ebay.com/itm/78-88-El-Camino-Monte-Carlo-Malibu-SS-dash-bezel-79-80-81-82-83-84-85-86-87-MINT-/330725394120
I prefer to mount these as shown, rather than @ 90 degrees, as the ability to pivot around a vertical axis generally provides a better range of sweep than if they pivot horizontally, but either way, these are in general a pretty good outlets.
More is better. Greater outlet area improves total airflow, albeit at a reduction in velocity. For instance, there may be some value in the elco/monte/bu example adding a second outlet on the RH side of the gauge cluster. At least for the driver, and he's (she's) the most important component in my book (because it's usually ME!)
Lose the convo tubing ducts. Build ducts out of Christmas wrapping paper cardboard tubing covered in smooth fiberglass resin. Cut pie sections and glue to make direction changes. Maybe ABS plumbing pipe? Smooth is good. Smoother is better.

Ill address other comments regarding the HVAC unit later.

[rfrankb4]

If anyone has any ideas, pictures and material lists for making better ducting for vintage AC units I would love to see them. I too have been considering making some smooth ductwork to increase air flow.

Additionally it will be nice that I can insulate it and not have the condensation dripping on my feet randomly as I drive.

I am with the others as well in that I am pleased with the performance of my GenIV unit in Alabama where humidity is frequently at 100% with temps 90-100. If I can get some ducts that better fit my specific application I would be tickled.

[INTMD8]

Modern cars flow 250-300 cfm (usually outside air measured with the inlet plenum pressure drop, blowing into a sealed body with zero body or specified pressure.) I don't believe any of the aftermarket A/C suppliers publish airflow volumes (I've never seen it), and have not objectively measured the Gen IV in my 70 Camaro. I speculate, based on airflow 'feel' (perceived volume based on outlet velocities) the system delivers no more than 140-160 cfm. Totally subjective estimate, I'd encourage the aftermarket to publish information. This is a full recirc system, so doesn't suffer the aiflow reduction an inlet plenum pressure drop causes.

This is the Gen IV blower motor if it interests you-

http://www.spalautomotive.com/eng/products/view_centrifugal.aspx?id=009-A70-74D

[Twentyover]

This is the Gen IV blower motor if it interests you-

http://www.spalautomotive.com/eng/products/view_centrifugal.aspx?id=009-A70-74D

Inadequate information to asses unit or system airflow. Every restriction in the unit or system results in pressure drops, and each pressure drop converts airflow into heat and noise. The restriction generated by the heat exchanger (I think the Gen IV use a combined evap/heater core), the housing, and the doors and ancillary parts is not addressed with blower only data.

I cannot speak for the aftermarket units, but assessing airflow by automotive OEM's is always done at the minimum of the unit level. As indicated in a prior post, frequently the inlet pressure to the blower motor is below atmospheric (inlet plenum pressure drop.) (This pressure drop can turn into a pressure increase as the vehicle speed increases. Reference info only, as unless there is a problem, in general OEM's do not look for airflow at elevated plenum pressures.They do, however, look for elevated brush temperatures at high ram.)

A simplified description of measuring airflow is as follows: The HVAC unit is secured and sealed to a large volume plenum. OEM specified voltage is supplied to the blower, and a bench blower is run to reduce to the large plenum pressure to either specified or measured values.An 'airflow machine', a variable speed blower pulling air through a venturi passing from another, small plenum into the machine's blower chamber. The small plenum is sealed to the unit port(s) being measured. Measure the pressure between the two sides of the venturi, and the airflow can be determined,either within the electronics of the machine, or in the old days we had charts that provided airflow to pressure drop curves, based on the geometry and size of the venturi. Same equipment type is used to 'collect the outlets', measuring airflow from each outlet to assure airflow distribution requirements are met. In general done on a production IP and ducts to assure all leaks and pressure drops are accounted for, in addition to the non-uniform airflow from the ports.

Each HVAC manufacturer has their proprietary blade 'lean' and geometry, and designs for the blower involute and cutoff (where the air is sheared from the blower wheel) and into the expansion area.Each has advantages and disadvantages, but if you buy the unit from a manufacturer, you buy his entire package, including the foibles of the designers designing the details of the specific unit.



If anyone has any ideas, pictures and material lists for making better ducting for vintage AC units I would love to see them. I too have been considering making some smooth ductwork to increase air flow.

Additionally it will be nice that I can insulate it and not have the condensation dripping on my feet randomly as I drive.

I am with the others as well in that I am pleased with the performance of my GenIV unit in Alabama where humidity is frequently at 100% with temps 90-100. If I can get some ducts that better fit my specific application I would be tickled.

You're getting condensate forming on the panel ducts? Honestly, I'm a bit surprised. I would think (there I go again) ambient added aspirated humidity would fall below the Gen IV's dehumidification capability. Another possibility is to provide a drip loop, a low point in the ducting where condensate collects, in an area away from your feet.

Next time I need a specialized duct, I'm going to try to form it from heavy construction paper or paperboard, then cover in fiberglass resin. Many production ducts are blow molded polypropylene with wall thickness 1.0-2.0 mm thick. Hardly structural.Last place I worked prototype ducts were made of SLA,and covered in carbon fiber if heat resistance was required