I received the warranty replacement control module from Angus Aviation in Australia late last week and started to test it again today with Brad's assistance.
When I initially hooked it up, things didn’t appear correct. The red led was barely lit and the other two leds were off. With an ambient temperature of 70f, my expectations was that only the green should be lighted. So I started doing some additional testing.
I disconnected the thermistor and replace it with a potentiometer . The green led came on right away. At about 11k ohms the yellow led lighted and about 14k ohms the red led lighted. This validates that the control and led modules are functioning as intended.
So my attention was then focused on the termistor. When the pitot heated, the thermistor resistance dropped to zero fairly quickly. (At 70f ambient temp, it didn’t take long to get extremely hot). So I then placed a bag of ice on the pitot. The thermistor resistance started to climb quickly to 11-12k ohm. Again, this seemed to work as anticipated.
I hooked the thermistor back up to the control module and everything was dead again. Breaking out the voltmeter, the white wire was at 0vdc, which I believe is normally supposed to be 5vdc at all times. This got me thinking. I tested the resistance from each thermistor lead to ground. Sure enough, one of them was shorted to ground.
My assumption is that the thermistor is supposed to be isolated from ground and that this short is what is causing this issue. Since the only place that this short can occur (since I can visibly inspect the leads) is internal to the pitot casting.
I'm awaiting for a response from Andrew (Angus Aviation) on how he wants to resolve the situation.
