At 05:56 AM 10/16/2014, Frank Condelli wrote: >The number one reason the coolant light flashes "slowly" when that >reservoir is full is because of a faulty coolant level sensor. They >are cheap, I sell them for $9.95 and Frank, this is a mistake. The flash rate is built into the LED inside the temp gauge -- it's a special flashing LED that operates on five volts. Inside the gauge it's in series with a 5.1 volt zener diode that drops the ten volt gauge supply to what the LED can handle. You can replace the gauge LED with a brighter one by replacing the zener diode with a load resistor; but if you want it to flash you have to use a self-flashing LED (which may or may not work as a drop-in to the original). The coolant level controller when triggered loads down the gauge sender line with </= 35 ohms to simulate an overheat condition. The gauge has no "idea" it's being tricked. The old-type controllers did this continuously, so the gauge needle would show overheat; but the newer cube-shaped ones only do it in brief pulses, long enough to trigger the flash but not long enough to disturb the gauge appreciably. Any time the flasher is triggered it runs for a couple seconds, so the controller only has to pulse every second or two to keep the flashing going. Long ago I analyzed the circuit to component level of the older controller and I understand exactly how it works in detail (or did at the time, anyway. It's quite a clever circuit). The newer ones have been collapsed into a single integrated circuit but behave essentially the same way. Yours, David ps - there are two or three different p/ns for the newer controller; they all work the same and there's no preference among them. All are hugely preferable to the old one as they don't peg the gauge on a low-coolant alarm. |
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