The pressure switch is a small round part,it has two wires running to it with a small rubber tube attached

Hi,
No tubes going into the inducer fan at all, at least not from the front or sides. There is a place at the upper right corner where you could put a tube in. In the manual it says this is where you pour tap water to prime the system drain before you start the furnace, but there is no tube in there now. I see a little drop of water in the hole, which is open. No plug in it, as I think there is supposed to be.

I've attached the photo. The disconnected tube is hanging out the front of the furnace, and in the lower left hand corner of the main compartment you can see where I plugged a little wad of white paper towel into the hole in the front of the furnace. That tube comes out the back of the pressure switches.

The two silver round parts with a tube between them is the pressure switches. Reconnect the drain.

Here is a pix of the whole front of my furnace.

Sorry, a little fast on the trigger. I reattached the hose.

The small rubber tube hanging in the front,where was it connected?

You see that kind of u-shaped tube that goes into the front of the pressure switches? If you look at the back of the pressure switches, there is an identical little u-shaped hose, but there is a t-connection in the middle of it and that tube comes out the back, and the other end goes into the front of the furnace where the paper towel is.
I didn't see any other tubes from the pressure switches that went into the front face of the furnace. The one that comes out the side and goes upward is plugged into what looks like the part that brings gas into the furnace.

Ok. Put all of that stuff back together. Next, check the intake and exaust pipes from the furnace all the way to the basement wall, make sure there are no bellies in the pipe that might be holding water.

Will do. Be right back

Hmm. Both pipes seem completely straight to me. It is a pretty long expanse, about 20 feet maybe, from the furnace to the outer wall. The pipes are supported by hangers, which sounds goofy, but it all looks very solid to me.
I was outside and could see nothing in the tubes. The tubes are 3" diameter, pretty big.

Ok, should be fine then. How long has it had this problem? And does it always give you the same code?

Now that the tube is back in place, is it OK if I turn the furnace back on? It is getting kind of cold in here.

Well, let's see how it does tonight since you drained all of the water out of it,I will check back with you after work tomorrow to see how it did. It's late here and I need to get to bed.

Yep, turn it back on

No, mostly it gives me 31, sometimes 32. Once or twice it gave me 42, which means blower calibration fault, but mostly it is 31 and 32.

This problem started sometime in the middle of the night last night. When I woke up it was 59 in the house. I have the thermostat set at 65 late at night. That night we also had a snowstorm with a lot of wind.

Thank you so very much for your help. I appreciate it. Sweet dreams.

And it hasn't ran right since?

Correct. Go to sleep! I don't want you to be without sleep tonight. We are in the same time zone, it is late for you to be up if you work mornings.

Good morning,
I'm heading into work myself this morning, but thought I'd mention how the night went. It is working a little better. The furnace will cycle into the low heat mode and run for quite a while, then it steps up into the high heat mode, where the blower blows harder. It used to be that would kill the furnace, as soon as it would switch into high heat mode it would get the 31 code and shut down. Then maybe make a few more starts and quit.
Last night it ran in low mode fine, went into high mode, then got the 31 code, shut down. When it started up again, it ran in low mode then went successfully into high mode for at least 20 minutes. Stronger airflow, hotter air coming out of the registers.
But now it is back to the same problem, though it seems to run a little longer before it gets the 31 code and shuts down.
The house is staying a little warmer, 63, as opposed to 59 last night.

I have to go to work in a bit, will be home in the pm.
Thanks for giving this your thought.