So far here's what I've got -

1. Thermostat calls for heat.
2. The inducer fan blows air.
3. 24v is sent to the pressure switch.
4. The pressure switch does not close (there is no voltage on the other side).

Steps I've taken -

1. Jumping the pressure switch allows the furnace to ignite and run "normally."
2. I've checked the pressure tube for cracks, kinks, and clogs. Found nothing.
3. I've cleaned the port on the inducer fan manifold - it was not clogged.
4. Sucking on the tube from the inducer fan will close the switch.
5. I've removed the exhaust and intake pipes. The inducer fan seems to be moving a good amount of air, but not creating enough negative pressure to close the switch. I don't have a meter to test the pressure in the tube.
6. There was a bit of water in the pvc pipe coming from the inducer fan when I disconnected it. It seemed like condensation (I ran the furnace for a few minutes with the switch jumped).
7. The condensate drain pipes seem to be functioning properly and not plugged up - some water has dripped from them.
8. There doesn't seem to be any water in the tube or the switch.

Any help would be appreciated!

Thanks,

Keith

You really need to find out the actual water column (vacuum) reading and compare it to the pressure switch rating. Draft inducer could be running a little slow or sucking in air around the gasket area. Fan blades may also be bad.

So, I built a manometer with water and measured the vacuum of the inducer fan. It read 2 inches of water pressure, but I'm not sure what the switch requires to close (it doesn't say anywhere on the switch).

Today, there seems to be a bit of water in the exhaust pipe and there is definitely water in the inducer fan, and the furnace will not ignite (I had the pressure switch jumped and had ran the furnace for about 15 minutes today).

Any thoughts?