Automotive Air Conditioning Information Forum

I am driving a 63 Pontiac Catalina convertible. Had it for about 10 years and the first modification was a new engine and trans. LT and 6 speed trans out of a 15 silverado. Had to adapt an A/C and found a unit out of a 96 Crown Vic that could be adapted. I got it in the available space but with all the ductwork I needed to manufacture with the fan in high it has the air flow of the average unit with the fan speed on 2 of 4. All the twists and turns cause so much restriction that I need a much more powerful fan. What is the most powerful firewall mounted fan that I can adapt to my mess? I am using the silverado compressor, condensor and evaporator so cooling is not an issue. I can get a 40 degree outlet temp on a hot So.Cal. day so cooling is not the issue but with a rag top and uncoated windows the heat loss is terrific. I need more airflow. I figure what I missed in design I can overcome with horsepower. (50's thinking) I will probably need to build a fan housing so are there any general rules for design. I built the current housing and with the inside unit out it is pumping a hurricane through the firewall hole but apparently there is too much restriction and possibily lack of power that is killing the present unit.

I dont know how the factory air was constructed but I do know that they had massive air flow and I would rather not have to re-design my unit.

Thanks, Dwight

grumpy old man wrote: Fri Mar 27, 2026 6:29 pm I got it in the available space but with all the ductwork I needed to manufacture with the fan in high it has the air flow of the average unit with the fan speed on 2 of 4. All the twists and turns cause so much restriction that I need a much more powerful fan.

Have you tried larger-diameter round duckwork? Usually, flexible round duct for automotive systems measures only 2" or 2-1/2". A 3" or 3-1/2" round flex duct, if you can fit it, will flow considerably more air than, say, a 2" flex duct. Also, try to minimize the use of elbows or tees in the system that will reduce airflow even more.

grumpy old man wrote: Fri Mar 27, 2026 6:29 pm What is the most powerful firewall mounted fan that I can adapt to my mess?

Seems to me that for the most powerful blower motors, you should be looking at an RV or commercial truck blower motor, such as a Danhard unit. Chances are, they will be the most powerful blower motors in the aftermarket that might suit your application.

grumpy old man wrote: Fri Mar 27, 2026 6:29 pm I can get a 40 degree outlet temp on a hot So.Cal. day so cooling is not the issue but with a rag top and uncoated windows the heat loss is terrific. I need more airflow.

Sounds like the transplanted Ford refrigerant system is working fine. It's the greater volume of airflow that's mainly needed.

For blocking UV rays, tinting the windows is a way to reduce sun glare and cabin temperatures. I would imagine that there must be a lot of shops that specialize in window tinting in Southern California. Additionally, convertible tops are available with insulation, not only to block road noise but also to reduce cabin temperatures.

I have been talking to a lot of people on the "net" and probably the best response was to go to a brushless motor. Apparently they have the most power available for fan motors, a lot more power than a brush motor. Now my problem is to find a controller for a brushless motor. Will be doing a lot more research on that one.

FYI I found that the restriction is in the GM evaporator, not in the ducting. Without the evaporator in the system the air flow is hurricane velocity but the Ford fan motor does not have the necessary power to overcome the restriction in the GM evaporator.

When I grew up in the dark ages, when we had to scoop dynosaur poop off the front lawn there were no manufacturers like I think it is classic air. Had I known about them I would have gone that route but 20 20 vision is only hindsight.