no error light flashing but still have pressure switch problem


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Old 02-10-16, 04:50 PM
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no error light flashing but still have pressure switch problem

Hi everyone,
So my furnace is a two stage amh95 I was getting a 3 blinking light signal indicating the pressure switch was closed. I have cleaned everything no clogs anywhere and tested the pressure switches and replaced the one that seemed to be not working correctly and still have the same problem without the flashing light. I replaced the inducer blower and circuit board and hoses and still no change. It cycles through the inducer blower starts igniter lights the gas does not turn on cycles through 3 times and locks out, if I suck on the pressure switch hose that is connected to the pressure switch next to the gas valve the burners ignite and it works. So my question is. If there is no error code could it still be the pressure switch? And if not what else could it be? Cheers Simon
 
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Old 02-11-16, 12:38 PM
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The hot surface ignitor should get white hot, then the main burner gas should switch on and light off the hsi.

Since that last step isn't happening, you should check:

1) Be SURE you have gas turned on at all points! The meter must be turned on or you must have propane in your tank. The meter or other gas valve must be on. The furnace shutoff valve must be on. The electric gas valve must be turned to the on position.

If you have other gas appliances that are working normally, some of those checks can be skipped.

You MUST have gas!


If all that is fine, use a multimeter to check for 24 VAC across the electric gas valve connections.

After the HSI heats up, you should measure 24 VAC being switched on to turn on the electric gas valve. If that voltage is present and the gas doesn't switch on, you probably have a bad gas valve that will need to be replaced.

If no voltage is switched on, you probably have a bad circuit boarde which is failing to turn on the main burner gas.
 
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Old 02-11-16, 01:29 PM
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Since everything works fine when you apply slight vacuum to the pressure switch, I would think most likely issue is plugged orifice into the inducer tube where the hose attaches. Clean it with small drill bit and make sure you slide it in far enough, at least and inch or so. Then reattach the hose and test again.
 
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Old 02-11-16, 04:11 PM
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Buying a manometer would have been less expensive than those parts.

Condensing furnace will lock out the furnace at the pressure switch if they get a drain problem.
 
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Old 02-12-16, 01:47 PM
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If the pressure switch were open, the hot surface ignitor would not heat up.


So the issue is why you are not getting the main burner gas to turn on.
 
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Old 02-12-16, 06:11 PM
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This is why I mentioned when you started another thread that things get confusing.
I believe there are three or four threads on this issue.

All the questions in this thread were addressed in the following thread and you furnace is still operating incorrectly.

http://www.doityourself.com/forum/ga...not-light.html
 
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Old 02-13-16, 08:00 PM
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Hi Seattle pioneer,
I have checked the gas valve with a multimeter and it is getting power, if I suck on the bottom pressure switch when the ignition sequence is going the burners light up. I have changed the tubing and all nipples are clean, it seems like there is not enough vacuum coming from the coil cover nipple to close the pressure switch, so I got a new inducer and it didn't solve the problem. If I swap tubing from the nipples to the pressure switches the burners fire up. I bought a new circuit board as was running out of ideas. If you can think of anything else to check I would be very appreciative
 
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Old 02-14-16, 03:15 PM
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First ---- quit sucking on the pressure switch. You can easily damage it or get it out of calibration, and the correct operation of the pressure switch is an important safety issue.

The pressure switch checks to verify that the furnace combustion air, venting and condensate drain system are all functioning properly. Since you pressure switch isn't closing, you have a defect in these systems.


As I understand it, you have verified that the pressure switch rubber tubing is not damaged with holes or splits.

Then take the tubing off the fitting on the inducer motor housing and use a paper clip or small drill bit to be sure that the fitting isn't plugged with rust or debris. Be sure you clean it out all the way into the inducer motor area.

After that, check for any sags that allow water to accumulate in the PVC pipe.

If that doesn't help, take out the bolts holding the inducer motor assembly in the furnace and inspect the inducer motor for plugged or broken fan blades, a motor that doesn't come up to speed and look for water or debris accumulating in the heat exchanger behind the inducer motor.

Accumulations of water would suggest that the furnace drainage system is plugged up and needs to be cleans of algae or other debris. You should be able to pour water into the heat exchanger exposed by removing the inducer motor and verify that the water is draining through and out of the drainage system.

Odds are good that one of the problems described above is causing the issue you have.
 
 

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