ClimateTalk Diagnostics - Communication Wiring and Testing - Bias

Air Handler w/ built-in EEV or Cased EEV and Horizontal Inverter:

C - 1 = 2.8 VDC

C - 2 = 2.2 VDC

Modulating Furnace w/ Cased EEV and Horizontal Inverter:

C - 1 = 2.8 VDC

C - 2 = 2.2 VDC

2 Stage Furnace w/ Cased EEV and Horizontal Inverter:

C - 1 = 2.3 VDC

C - 2 = 1.7 VDC

2 Stage Furnace w/ Cased TXV and Unitary Inverter:

C - 1 = 1.9 VDC

C - 2 = 1.3 VDC

There should always be a ≥0.6 VDC - ≤0.9 VDC Bias between terminal measurements of 1 and 2

(Measurements of C-1 minus C-2) 

Troubleshoot and Fix the Network:

1. 24 VAC should be available at each circuit board terminal block, except outdoor Inverter units.
2. Measure the BIAS (VDC) from "24 VAC common" (chassis ground) to "terminal 1 & 2" at each circuit board terminal block:
   • If the BIAS voltages read the same (ie. 2.3 VDC & 2.3 VDC) the data wires are shorted together. Find the Short and Fix it!
   • If one BIAS voltage reads OK and the other reads 0 VDC (ie 2.3 VDC & 0 VDC) one of the data wires is open... Find the Open wire and Fix it!
3. If the BIAS voltages read slightly different (ie. 2.2 VDC & 1.9 VDC) then measure the (▲ - DELTA) straight across terminals 1 & 2.
   • If the reading is less than 0.6vdc (ie.3 VDC or 0.4 VDC), the network is not stable and may not support high volume data.