1968 Firebird.
I want to trigger electric fan override and an idle bump solenoid during AC use.
I'll use a circuit that's +12v with ignition on with a lighted push-on/push-off switch below the dash.
Both items are relatively low current users, but I want to ensure neither are backfeeding each other or the fuse panel.
I'd like to use blade type diodes to fit in fuse holders at each point of connection.
What size diodes?

 

Choose a diode that can handle more current than the fuse you're connecting to.

Here's a 40 amp diode just in case you need that much capacity.
https://www.digikey.com/en/products/detail/ixys/DH40-18A/1994853
I don't know how much current whatever it is you're controlling, so better to over engineer than to under. Right sizing is the best way to go but that link will get you in an area where you can make a decision on what diode you want.

Here's the main page
https://www.digikey.com/en/products/filter/single-diodes/280?s=N4IgTCBcDaICwAYCCACAJgSwPZoKYgF0BfIA

 

Both items are relatively low current users,

How low?

Relative to what? Relative to the starter motor, 5 A is low current.

It's a diode. You had to know that we cannot recommend a part number without knowing the current.

ak

 

Please help?
Going to use a 5 amp fuse.
So a 10amp Diode?
I'd like to use a blade type.

 

Please help?
Going to use a 5 amp fuse.
So a 10amp Diode?
I'd like to use a blade type.

https://www.digikey.com/en/products/detail/smc-diode-solutions/SB10150/6022603
finding a "Blade Type" will be challenging. But in post #2 there's a web page. From there you can enter what you're looking for and find it.

 

1968 Firebird.
I want to trigger electric fan override and an idle bump solenoid during AC use.
I'll use a circuit that's +12v with ignition on with a lighted push-on/push-off switch below the dash.
Both items are relatively low current users, but I want to ensure neither are backfeeding each other or the fuse panel.
I'd like to use blade type diodes to fit in fuse holders at each point of connection.
What size diodes?

WHAT does the TS mean by "an electric fan override"??? I would guess that it would be a scheme to bypass the thermostat that operates the radiator cooling fan. In that case the TS REALLY needs to know how much current that fan motor requires. I can see the insulation melting off of the wires before it starts burning.

 

Here's a novel idea:
Use a relay to activate the fan when the AC is on. As far as the idle bump? Perhaps an air leak might do the trick. They used to make solenoid air valves that go on a vacuum line. Opening a manifold vacuum line, a small one, might give you the bump you are looking for.

I used to drive a 72 Chevy Nova - gaud I loved that car. Wish I had it now. Back then everyone was trying tricks to improve gas mileage. To date nobody has found a good way to improve mileage. However, I had a solenoid valve and connected it to the manifold vacuum. When activated - it increased the idle. Don't ask me how much, but you could hear the engine idle come up. Of course back then I didn't understand I was running the engine lean and putting more pressure on the pistons due to running lean. But lean running was the idea behind that. IF you choose to bump the idle that way - understand there could be consequences.

You're talking about a 68 Firebird. If the choke advance cam is still in place, you might find a way to hook up a solenoid to that to bump the idle up one click. As I can recall, that cam had 3 or 4 steps. As the engine warmed up the cam stepped down one notch based on how much the automatic choke had moved. Man - such simple times. Today's engines require Special High Intensity Training and a degree in astrophysics. In my lifetime I've gotten plenty of Special High Intensity Training. S. H. I. T. for short.

 

Looking back at post #1, does the vehicle already have those functions in operation?? OR, is it possible to use a newer body control computer to make them available??
Those were standard on our 1969 Sport Satellite.

 

A schematic of that vehicle would be convenient to check what can be done.
A vacuum leak to trick idle will cause more coolant heating even overheating.
For the not lazy, removing the thermostat and blocking the coolant bypass path from May to November is very good insurance if radiator is healthy.

 

A vacuum leak to trick idle will cause more coolant heating even overheating.

I hadn't considered that. But it seems logical. More air means running leaner, producing more heat. But if the goal is air conditioning, the condenser core is mounted in front of the radiator. Even under normal operation the condenser will heat the air before it reaches the radiator. So either way - you're pumping more heat from the interior of the car to the outside. While running lean may mean more heat I don't think I've ever seen any problems with engine temperature way back in the 70's when I was doing that trick. Still, since you sound the warning I'd like to remind all that I had mentioned that originally.

I had a solenoid valve and connected it to the manifold vacuum. When activated - it increased the idle. Don't ask me how much, but you could hear the engine idle come up. Of course back then I didn't understand I was running the engine lean and putting more pressure on the pistons due to running lean. But lean running was the idea behind that. IF you choose to bump the idle that way - understand there could be consequences.

IF you choose to bump the idle that way - understand there could be consequences.

I did say there could be consequences.

For the not lazy, removing the thermostat and blocking the coolant bypass path from May to November is very good insurance if radiator is healthy.

There can be consequences to this too. Forgetting to put the thermostat back in the engine could mean running the engine cold and never getting up to temperature. Also, running the coolant through the radiator too fast to cool it down could lead to overheating as well. Not to mention the work involved in taking it out and putting it back in. Coolant leaks can occur and spilling coolant on the ground all have negative effects.

 

Hi Tony.

...running the coolant through the radiator too fast to cool it down could lead to overheating as well...

Sorry, that is the biggest myth in automotive mechanics ever ; to say it politely, it is much worse than the other myth saying that a battery self-discharges set on pavement. ( and NOT to be part of this thread ! please)

I have it easy; 2 screws to remove the thermostat... 1 minute.

 

Perhaps a myth, perhaps not. Personally I've never seen any evidence to support or to bunk the idea. But I can accept that I might be wrong. But I do know this much - an engine needs to come up to temperature in order to run properly. A cold engine wastes fuel and emits more pollutants. But the thread isn't about fuel saving it's about utilizing AC more efficiently.

I am unaware of automobiles from back in the 60's having electric fans. Best I recall is clutch fans driven by belt, or fans with flexible blades producing less drag on the engine.

 

NO, not about " utilizing AC more efficiently. " It may be about increasing the cooling a bit. My suggestio relative to that is to clean the evaporator assembly and the blower blades and passages.

 

it's about utilizing AC more efficiently.

It may be about increasing the cooling a bit

Isn't this the same thing? More efficient means more cooling. No?

 

WHAT does the TS mean by "an electric fan override"???

We do not know if it is the evaporatorAC fan or the condenser/radiator fan. 'Overriding' It can be turning off the condenser/radiator/evaporator electric fan when it is on properly doing its thing; or the opposite, can be turning that fan on when is not needed/operating. We do not know.

The 'fast idle' solenoid should abound at stores or boneyards.

 

In most automotive systems the condenser, located in front of the radiator, uses a FAN. In the cooling section, without exception in cars, the air is moved by a blower.
And the BLOWER would never be switched off because that stops the cooling effect immediately.
So it is a very reasonable thing to guess that the TS is wanting to be able to switch on the outside CONDENSER FAN to provide more air flow thru the radiator, for additional engine cooling in some of those nasty traffic jams. It may be that the engine computer is not correctly reading the engine temperature. THAT is a separate problem.

 

No compfusers in a '68... Only my '62 got a transplanted one.