In the 1-ON-1 mode, the FIT is only connected to a single controller that is not connected to a network. The communication voltage readings in this mode should be in the range of 4–10 VDC differential voltage and 2 to 5 VDC for the +, – line voltages. The important thing to note is that the + and – line readings typically are equal or within approximately 0.2VDC of each other. The + line voltage will usually read equal to or slightly higher than the – line voltage. See Figure 21 for an example.
If the readings taken are below 4V differential or the + and – readings are not within 0.4VDC of each other, then the controller may be damaged. Damaged controllers typically have a larger voltage difference (greater than 0.4VDC) between + and - readings. See Figure 22 for an example.