This is actually a continuation of the thread
https://www.fiatforum.com/bravo-brava/84922-brava-automatic-cold-start-noise.html
whose topic drifted away from the original "transmission noise" problems towards the engine cooling problem. In short, my car would wait until the temp gauge needle gets well over mid point (but before the red section) before the fan would kick in. It would then cool it down close to the mid point and then the cycle would repeat.
Thanks to jug, I learned more about the cooling system, collected some wiring diagrams and inspected the temp sensor and all the relays and connections. Everything was functioning normally, except for the last piece in the chain which was at fault - rusty contacts on the fan limiting resistor.
The fan in the version with A/C has actually two supply circuits, one coming directly from the (high speed) relay, and the other from the (low speed) relay connected in series with a limiting resistor. The purpose of the resistor is to reduce the voltage of the fan and thus make it run at lower speed. The resistor is located directly on the fan housing (for cooling purposes, because it dissipates a lot of heat) and has a very small resistance (about 0.5 ohms).
All connections in the fan circuit have to be very clean and virtually 0 ohm resistance, because the fan draws very high current (probably over 10 amps). Just 0.5 ohm extra resistance (in addition to the limiting resistor) would prevent the fan running at all, because it needs some minimal starting voltage (probably 5-6 volts). For those having problems with cooling system I strongly suggest inspecting ALL the contacts in the fan circuit before checking out the components. Remember that version with A/C has two circuits.
After cleaning the contacts and having a test drive, I finally celebrated my first encounter with the fan "low speed", and saw the temp gauge needle traveling just a short distance above the mid point
.
It seems that the version with A/C has a different operation depending on whether the A/C compressor is turned on or off. If it's turned off (this can happen even when the A/C is in use, because the compressor turns on and off periodically), the fan would first start at low speed. Only if the temperature rises further (you will see the needle traveling more towards the red section), the high speed relay kicks in.
If the A/C compressor is on, the fan runs at high speed only and kicks in at the same point where it would kick in at low speed when the compressor is off. Does anyone have a different interpretation or experience?
https://www.fiatforum.com/bravo-brava/84922-brava-automatic-cold-start-noise.html
whose topic drifted away from the original "transmission noise" problems towards the engine cooling problem. In short, my car would wait until the temp gauge needle gets well over mid point (but before the red section) before the fan would kick in. It would then cool it down close to the mid point and then the cycle would repeat.
Thanks to jug, I learned more about the cooling system, collected some wiring diagrams and inspected the temp sensor and all the relays and connections. Everything was functioning normally, except for the last piece in the chain which was at fault - rusty contacts on the fan limiting resistor.
The fan in the version with A/C has actually two supply circuits, one coming directly from the (high speed) relay, and the other from the (low speed) relay connected in series with a limiting resistor. The purpose of the resistor is to reduce the voltage of the fan and thus make it run at lower speed. The resistor is located directly on the fan housing (for cooling purposes, because it dissipates a lot of heat) and has a very small resistance (about 0.5 ohms).
All connections in the fan circuit have to be very clean and virtually 0 ohm resistance, because the fan draws very high current (probably over 10 amps). Just 0.5 ohm extra resistance (in addition to the limiting resistor) would prevent the fan running at all, because it needs some minimal starting voltage (probably 5-6 volts). For those having problems with cooling system I strongly suggest inspecting ALL the contacts in the fan circuit before checking out the components. Remember that version with A/C has two circuits.
After cleaning the contacts and having a test drive, I finally celebrated my first encounter with the fan "low speed", and saw the temp gauge needle traveling just a short distance above the mid point
.It seems that the version with A/C has a different operation depending on whether the A/C compressor is turned on or off. If it's turned off (this can happen even when the A/C is in use, because the compressor turns on and off periodically), the fan would first start at low speed. Only if the temperature rises further (you will see the needle traveling more towards the red section), the high speed relay kicks in.
If the A/C compressor is on, the fan runs at high speed only and kicks in at the same point where it would kick in at low speed when the compressor is off. Does anyone have a different interpretation or experience?
