Recommended Engine RPM with A/C on
 

I have researched this and have not found a satisfactory answer so I thought I would just ask everyone. I have a 65 GTO with a 69 428, 5 speed, 3.36 gears, and a Vintage Air system. I am running an aluminum radiator, good water pump with good clearances, and a Flex-A-Lite 7 blade fan with a factory shroud. I have never had any issues with overheating. As a matter of fact the engine runs around 180 degrees most of the time. I have the idle RPM set at 700. Then on July 3rd the local nursing home had a cruise-by car show for the residents so we took the GTO. It was in the low 90's and very humid that day and we were in stop and go traffic and never exceeded 5 MPH. We had the air on and the temperature shot up and pegged out the gauge, not good. Once we got out of the traffic it instantly came back down to 180 degrees, still running the air.

I have since then sealed up the stock fan shroud to the radiator with foam to ensure that the air will only be pulled through the radiator. I have the Holley Sniper EFI and can set it up to where the idle RPM increases when the air is on which would increase the air flow through the radiator as well as make the water circulate better. My question is what would be a good RPM to increase it to. During my searching I found that the recommended idle speed for a 69 428 with a manual transmission is 1000 RPM with or without the air on. I was thinking of pumping the idle up to 1100 RPM with the A/C on which is the RPM the EFI uses to warm the engine up. What do you guys think would be a good RPM to start with?

I really don't want to make any other changes, like a different fan, because what I have works really good. Even idling for extended periods in the garage with the A/C off it rarely gets above 180 degrees. I am thinking that with the A/C condenser mounted in front of the radiator that when the A/C is on the added heat from the condenser is pulled through the radiator making it even hotter. My last choice would be to put a dual electric fan system on it and let the EFI control the fans, but I would want one that is a direct bolt on and comes with the shroud that fits my radiator.

Thanks for the help,
Dale

i have air and fitech on my 70gto with electric fans. if you dont want to change what you have maybe add a pusher fan controlled by both AC on signal from the vintage air AND a set temp on your EFI. simple relay control can use both signals in order for fan to turn on. you will need a trinary switch on the AC to control fan. EFI usually completes ground on control side of relay when programmed temp is reached.

I had really fought the urge to put electric fans on the car when I built it but decided to go with the manual fan instead. A pusher fan won't work because of where and how the A/C condenser is mounted. These are the fans I had originally thought about using, https://www.summitracing.com/parts/der-16927, and I might end up that route if increasing the RPM doesn't keep it cool. Like I said, up until now the manual fan and setup I have has done a great job. But I don't run the air a lot unless the wife is with me, she likes the air. The Sniper EFI has the ability to control two fans so you don't need the trinary switch. You can even set it up so one fan turns on as soon as the air is turned on while it is also controlled by temperature if the air isn't on.
Thanks for the response,
Dale

My normal idle speed is around 850 for a nice lope, but I have the electric solenoid on the carb set to increase the idle to around 1,050 RPM with the A/C running. Helps a little with engine temps but it also seems to keep the A/C outlet temps in the car a little cooler when sitting at a light. A little extra air flow through the condenser and radiator is never a bad thing.

Increasing my RPM to 1000 with the air on did not help the temperatures any so I have decided to put a dual electric fan system in it from Derale. I figured it is an air flow issue because all I have to do is set a fan in front of the car blowing into the radiator and the temperature starts to drop. These should make things a lot better. Plus I am going to upgrade the alternator from 94 amps to 150 amps and add 2 gauge wires for the ground and alternator wire to handle the additional load. Should be a nice upgrade. These are the fans I ordered which get really good reviews, https://derale.com/product-footer/el...s/16825-detail. I am thinking of painting the shroud black to match the radiator and support so the aluminum doesn't jump out at you when you look in the engine compartment.
Thanks for the information,
Dale