# Snyder General Gas Furnace - No Gas to the ignitor



## #CARRIERMAN (Oct 18, 2006)

Hi Hanela

First thing we need to know is if you are hearing a little fan come on before the ignitor glows. If you do thats a good start. Second, it sounds like you have a voltmeter. Turn it to AC volts, put one lead on either connector on the pressure switch. The meter should be reading zero volts if the inducer is running. If you are reading any voltage at all the pressure switch is not closing for some reason. Remove the hose from the collector box and blow lightly into hose and suck lighty on the hose. You should hear a faint click, when you hear the click hook the hose back on to collector and start furnace up. If the furnace works you need to replace the pressure switch.

Good luck
Rusty


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## Hanela (Nov 30, 2006)

Rusty,

No I'm not hearing any faint noises coming from my furnace. I figured there has to be some type of blower to evacuate any residual gasses and to pull a draft. Thanks for the information in regards to checking the pressure switch. I'll give it a try this weekend. 

Craig


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## HvacWiz (Nov 24, 2006)

*I dont think there is a presure switch problem since you said ignitor glows red hot. Ignitor will not glow unless presure switch contacts are closed. have you checked for 24v at gas valve after you see ignitor glowing? Good luck *


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## #CARRIERMAN (Oct 18, 2006)

Hi HvacWiz

Not all furnaces have the same sequence of operation. I believe on this furnace it uses a sperate ignition control. All the pressure switch does at this point is determines rather or not the gas valve may open. The ignitor circuit is seperate from the safety circuit. Not for sure, but that is how the Comfortmaker and Arcoaire used to be.

Rusty


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## Capaz (Dec 4, 2006)

Although unlikely, even if the microswitch mechanically operates (Faint sound) it is not guaranteed that electrical conection is made.

The switch could be normally open (N/O) or normally closed (N/C). (it is likely to be N/O)

Disconect the wires going to vacuum sensor microswitch. Determine if it is open or closed when power is off. Then create the opposite, by shorting the wires coming to the switch if the switch is N/O, or leaving the wires hanging away from each other (and the frame) if N/C.

The above process will not work if the microprocessor checks for switch condition *BEFORE* aplying power to the vent pipe blower. In other words for a N/O switch, first the microprocessor checks for the switch to be open before powering up the vent blower, waits a few seconds and then checks again for the switch to have closed. It depends on how sophisticated the furnace design is.

Comment on the valves, if they operated off line with nominal voltage, then it is obvious that 24 volts are not being provided by the main board. 

If you are familiar tracing Printed circuit boards, then locate the gas valve relay and install in parallel with the closing points a *temporary* switch which you could operate by hand after the igniter is glowing. If gas flows, the relay is not operating because it is defective or the micoprocessor is not sending the voltage to operate the relay. You could also check if voltage is present on the relay coil (at the time that gas should flow)

NOTE In this case, *temporary* means two things, the fact that you are going to remove it later AND that the switch only closes the circuit WHILE you are operating it, and will open the circuit as soon as you let go. (Extra safety precaucion)

Just be careful and good luck
Abel


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