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designing a fan circuit

boomdriver

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Dec 18, 2008
Messages
1,888
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texas
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87 z-51
This is going to be a fall/winter project along with a stack of others...

After this summers brutal ambient temps that would overwhelm my a/c condensor at idle in traffic and send the system to high pressure where it would cut out and leave me sweating until the lite turned green, I've decided to re-install a fan up front. This is going to have to be a face mount on the condensor since my oil cooler now rest where the Aux fan once lived.

What I want to do is install a fan big enough to cool the condensor when there is no or minimal air flow...like in traffic on a hot day. The sucker fan pulls plenty of air, around the condensor (by design) to the radiator. The system prioritizes the air flow when its limited.

I want to find some way of making this as automated as possible. Not waiting until 238 degrees like the factory aux switch will do. I am thinking about a lower temp switch to go in that same place, if available to turn the new fan on at 190-200...soon enough that it won;t let the a/c go to high pressure shut off.
IF such a low temp switch exist that will fit that hole in the driver side head.

OR

wire in a relay that would trigger the new fan whenever the a/c is turned on much like the main fan is set up to do... If I am thinking right all that needs is a fused power source then tap into the control ground that loops across the a/c switches for low press, cycling and high pressure so the ground path is completed tripping the relay and allowing the independent power source to run the new fan.

Last option would be a switch inside the cabin....although I already have a switch plate in the dash by the key, I'd rather not have to remember to use it...

Any thoughts?

If anyone does know of a temp switch that will fit the existing hole thats good for around 180-200 area, that would be great. I do not know if any other temp switch would fit...Like the CS switch in the front of the intake.
 

boomdriver

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1,888
Location
texas
Corvette
87 z-51

vetteoz

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1,564
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Not in Kansa anymore
Corvette
1990

Hib Halverson

Technical Writer for Internet & Print Media
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CenCoast CA
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71 04 12 19
I have a sneaking feeling that no amount of fussing with airflow through the cooling stack is going to solve the problem with the hvac.

If there's a problem with the high pressure side of the hvac such that the compressor "cuts out", I think I'd service the hvac such such that you correct the problem that's causing the compressor to cut out.

I just finished a 5200 mile trip in my C4 which took us through the hottest parts of the country....Texas east-to-west included. Even in the hottest part of the trip–across the eastern Mojave desert at mid-day–we never had a problem with the hvac compressor cutting out. This includes on 25-min idle period while we had a long visit to a convenience store near the middle-of-nowhere in Essex, CA. At that location, the ambient was 116. No problems with the hvac compressor there, either.

I think the AC can be made to work but a better approach is service that system, first, then address any issues with cooling air flow.
 

boomdriver

Well-known member
Joined
Dec 18, 2008
Messages
1,888
Location
texas
Corvette
87 z-51
I have a sneaking feeling that no amount of fussing with airflow through the cooling stack is going to solve the problem with the hvac.

If there's a problem with the high pressure side of the hvac such that the compressor "cuts out", I think I'd service the hvac such such that you correct the problem that's causing the compressor to cut out.

I just finished a 5200 mile trip in my C4 which took us through the hottest parts of the country....Texas east-to-west included. Even in the hottest part of the trip–across the eastern Mojave desert at mid-day–we never had a problem with the hvac compressor cutting out. This includes on 25-min idle period while we had a long visit to a convenience store near the middle-of-nowhere in Essex, CA. At that location, the ambient was 116. No problems with the hvac compressor there, either.

I think the AC can be made to work but a better approach is service that system, first, then address any issues with cooling air flow.

I don;t have a problem while driving in 110 degree temps. The a/c blows cold.

The problom arises when sitting at a dead stop in 110 degree temps with the a/c running. As you know, the main fan (sucker) pulls air into the cooling stack but the air thats drawn in is allowed to travel around the condensor by way of design. The system priortizes air flow when is limited supply.

That being said, the condensor is left sitting there with no air (or very very little) flowing across its surface. As air flows around the condensor while sitting still, as in heavy traffic or stop lights, the system pressure rises as it should since it IS collecting heat from the cabin for exchange in the airstream up front. Because the car is not moving and creating that airflow,. the system eventually gets to high pressure cut out. It only takes a few seconds of 20 mph or more to generate enough airflow to solve the problem and get system pressure back down low enough to allow compressor operation once again.

The aux fan was destroyed yrs ago by debris and never replaced. That space has since been utilized to place an oil cooler up front.
Everything is new....everything. Radiator, all alum oversized. Condensor,....a/c was "firewall forward" last spring.

The goal is simply to have enough airflow while sitting still to have some heat exchange at the condensor to prevent hi-pressure cut out and the loss of cabin comfort. I am planning on fitting a pair of 7.5" (300cfm each) Spal fans on a bracket right in front of the whole mess just above the air-dam so that they can pull air into the stack and get some against the condensor. If I have to I'll mount them ON the condensor so the maximum flow is thru the condensor and NOT around it thru the stack baffles that also route trash bags to the radiator..

the only question was how I could get fans to operate when I wanted them and make it as automated as possible. They would likely assist the main fan at cruise speeds as well if I get the right size/temp switch for the aux circuit.

Currently my engine will run a nice 190 degrees with a/c on driving at 70 mph on a toasty texass afternoon of 110 degrees. Its very efficient when its moving....Today at 90 degrees ambient, it was staying at 185-189 on the freeway with a/c. I can;t ask for more as far as cooling system performance while in motion. Its the stop lights and traffic that make my shirt stick to the seat back......
 

topless82vette

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Joined
Nov 1, 2001
Messages
910
Location
southern california
Corvette
1982 convertible (not factory) stock 350cfi auto
Just a thought, but couldn't you mount a 90up twin fan cooling capsule in the older vette? Then run both fans when needed?
 

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