honeywell smart valve

zepfan

we have been having intermittent problems with a furnace that has a honeywell smart valve, and a honeywell board of the following parts numbers.
valve part# sv9641m4510
board part# st9160b1084
my question has to do with how does the valve know when a call for heat is present, if there is 24 vac at all times, even when the furnace is not heating? what voltage level should be seen on the data line going to the valve from the board,when there is a call for heat,and then when there is no call for heat? I looked at the furnace today, and everything seemed ok, and the furnace fired fine. the dc voltage (if it is supposed to be dc) pulsed no matter what mode the furnace was in (heat call/no call) on the data line going to the valve.any assistance would be much appreciated. thanks to all

Tim McElwain

my question has to do with how does the valve know when a call for heat is present, if there is 24 vac at all times, even when the furnace is not heating?

ANSWER - There is a constant 24 to the Smart Valve and an interrupted 24, the interrupted 24 only occurs when the call for heat takes place by the thermostat. That sends voltage from the board to the SmartValve provided the 120 Volts to the valve switches internally in the valve and powers the draft inducer which in turn should complete the power through the pressure switch to the smart valve. This will cause the igniter to come on light the pilot, prove the flame with a 2 to 10 microamp signal minimum 1.3 microamps. The valve should then open and a 15 to 28 volt AC signal should appear on the EFT output wire (data back to the ST9160 to trigger the fan start time sequence).

what voltage level should be seen on the data line going to the valve from the board, when there is a call for heat

NONE until the valve opens and then the data is sent to the board.

, and then when there is no call for heat? NONE

I looked at the furnace today, and everything seemed ok, and the furnace fired fine. the dc voltage (if it is supposed to be dc) pulsed no matter what mode the furnace was in (heat call/no call) on the data line going to the valve. any assistance would be much appreciated. thanks to all

Data is the language the microprocessor on the board needs in order to control the on time of the system fan. There may be a DC signal there all the time but it does not affect the overall operation of the system.

zepfan

thank you some much for your response, and time. I know have a better understanding of how this system works. The only thing I am still not clear on is which 24 volt wire is hot all the time, and which one is hot only on a call for heat.When looking at the valve,field piping connection on right manifold connection on left, the six pin low voltage connection has 24 vac on the bottom left, and on the pin directly above that.Do you know which one is constant, and which one is switched? Thanks again.

Tim McElwain

The ST9160B pin connector P1 bottom two pins are the constant 24, middle one on the left is interrupted 24, top 2 pins are 120 volts and the middle on the right is the EFT (Data) wire. That is how the ST9160C is wired I do not have exact wiring for the B version but I think what I just gave you is probably correct.