I saw something saying that the circuits on a Venus bound space craft would overheat and basically ruin the the spacecraft.
Is that true?
If so, could they install fans to keep the circuits cool?
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Fans work by moving cool air (or other fluid) over a warm surface. If there is no air, like in space, a fan will serve no purpose. Cooling things in space is actually a bit tricky because of this - objects on earth tend to lose most of their heat through conduction or convection, but in the vacuum of space, all you can do is radiate heat, which a fan will not help with.
Venus does have an atmosphere, so a fan wouldn't be inherently nonfunctional for space probe on the surface of the planet. But since the Venusian air is several hundred degrees Celsius at all times, you're not going to have much luck cooling electronics with airflow - at that temperature extreme, your electronics will probably be cooling the air, rather than the other way around. If your electronics normally run hotter than the surface of Venus, though, then a fan would help to cool them, but that would be an absurdly high normal operating temperature - if your electronics can already survive that, you probably don't need to cool them in the first place.
Overall, fans are not a useful way of cooling the electronics of a space probe, unless you are somewhere with a cold atmosphere (like Mars), or bring your own heat-exchanging gas into the vacuum of space (see Are fans ever used in un-crewed spacecraft?).
The effect of a fan in an electronic device is to accelerate the temperature exchange between circuits and atmosphere.
But that temperature exchange works in both directions. When the atmosphere is even hotter than the electronics you expose to it, then improving the flow with a fan will make the part even hotter. That's the principle behind a convection oven or a hot-air hair dryer, by the way.
So adding fans to a probe which is supposed to stay below 100°C within the 450°C atmosphere of Venus would be rather counter-productive.
As pointed out, a cooling fan cannot reduce the temperature below the ambient. That doesn't mean it's completely useless in this case.
First, OP said "Venus-bound." In this case a fan could be used to transfer heat from sunward sections to shadowed sections, or even better to radiating heat sinks on the shadowed side.
Even when on the planet, it could be used to distribute air cooled by a centralized cooling system (which would likely need to be active, since most electronics are silicon-based and won't do well over 150C).
If high temperature circuitry is used that can operate at about 500C, a fan would still help distribute the heat generated by high-power devices.
Heat is exchanged via three mechanisms:
In the presence of an atmosphere, transfer via convection is usually the most efficient, followed by conduction. Radiation is -- by far -- the weakest form of heat transfer.
On the way to Venus, the probe is in space and thus the strongest form of heat transfer is unavailable. There is no atmosphere one could use to transfer heat from or to. This leaves conduction and radiation. Heat travels through the probe via conduction. The electronics heat the probe. But usually, conduction is not sufficient to heat all of the probe equally, it will still have hotter parts and colder parts. The excess heat is shed via radiation, usually with special devices aptly called radiators (which look a lot like solar panels).
But as you move closer to the sun, more heat is absorbed by the probe, while radiating it gets more difficult. The equilibrium temperature rises and the probe becomes hotter.
As soon as you enter the Venusian atmosphere, convection becomes available as a method of heat transfer and a fan becomes applicable. However, the atmospheric temperature at the surface of Venus is up to 470° C. Heat transfer works in both directions, if you blow hot air (or gases, or fluids) over a cold surface the cold surface becomes warmer (blow hot air over ice, it melts quicker).
So basically, a fan would just expedite the demise of the probe since the hot, acidic venusian air is allowed to efficiently transfer it heat to the electronics.
In order to remove heat, you need something colder you can transfer heat to. In space, there isn't any matter around you could transfer heat to, so radiation is the only option. That is why the ISS has such large radiator - it is to shed excess heat.
In the venusian atmosphere, you have matter for heat transfer. But that matter is already much hotter then the operating temperature of the probe, so you would typically try to minimize heat transfer so that the probe stays cool longer and have a longer working time.
Note that fans only feel cold to a human. A fan on your desk doesn't actually cool anything. A fan on your desk blows dry air that is the same temperature as room temperature over your skin. The sweat on your skin evaporates better since humidity is carried away in the air stream. It is the process of evaporation that locally lowers temperature since water needs energy to go from fluid to gaseous - this energy comes in the form of heat that is removed from your skin, making it feel colder.
You can, however, use a fan internally, e.g. to circulate gases or fluids inside the spacecraft to distribute heat inside the spacecraft, e.g. from a cold storage to warmer sections like the hull. In that case, the fan isn't used for cooling, though, but for circulation (cf. Are fans ever used in un-crewed spacecraft?). But you can not make the spacecraft colder per se with this technique, except when transferring heat that way to a radiator where it is then removed by thermal radiation.
Note that in any closed system, a fan necessarily only adds heat because it does work - the motor has to turn, with all that entails.
From the other side, devices under the link only support about 70 degree temperature difference so five must be cascaded for Venus, using 150 W in total that is very demanding for a battery operated spacecraft. The outer devices are also not protected from the Venus heat and must be able to withstand it.