BMA used Aerosance CHT probes for a while. These are not thermocouples, they are thermistors (temperature sensitive resistors). Are you 100% sure that you have thermocouple CHT's? A thermistor would act exactly like you describe.
You can check the probe with an ohmmeter. If it's a thermocouple, it will look like a dead short, with just a few ohms of resistance. If it's a thermistor, it will have much, much more resistance. I don't know exactly what to expect at room temp as I couldn't find a table for these probes in the few minutes I looked on-line.
If you want to prove that the thermocouple input is working, you can hook a 1.5V battery to one of the CHT input channels (AAA, AA, etc). This will cause it to rail out, reading 1800 degrees or -99 degrees depending which way you hook it up. At least you'd know the input is reading something.