We actually did that on this one. Took 24 v from board to valve, fired gv and ran without issue. Allowed us to rule out any issue w gas valve. First time I have done this, it also allowed us to run furnace long enough to trip roll out for good, leading to the root issue.
How exactly? You cycled normally and added another 24v to the GV, in addition to the 24v it might already be getting?
Or did you remove the existing wires from the GV? If so, how was the circuit completed?
Removed existing wires from gas valve. Used jumper from r and jumper from common. Once board gave call for gv, manually gave gv 24v from terminal block on board.
Not sure if this is a good thing or a bad thing, but it worked. Allowed us to rule out gv and find the real problem. Also able to determine gas pressure.
I guess it's fine if the GV relay and GV are on their own little circuit. I just grabbed the nearest Carrier schematic I have and it appears the pressure switch has a way back to common thru the CPU, so that unhooking the GV wires would not effect the rest of the cycle. I never bothered to notice whether most furnaces are likewise wired, always assumed all the safeties were wired in series with GV to shut it down if one opened.
Great idea, disconnecting existing wiring on the valve and running a 24 and common off the low voltage coming in, basically bypassing the board control, then testing the opening of the valve by the outgoing pressure..Thanks!
Also just remembered - disconnect the power supply and check for voltage between neutral and ground. Shouldnt have more than 0.5vac if so you may have a neutral/grounding issue. It's put an end to me banging my head against the wall before... on a Trane 90% if I remember correctly. Read between 15-25v while also getting 95-105v hot to ground.
I've measured up to 10 volts to neutral in the past. I thought this was just feedback. Could this be a clue that there is a problem?