[HVACTech]

When my furnace tries to come on it blinks 3 times which tells me my pressure switch failed to close. I went and got another one and put on and it is still doing the same thing. When I jumper it out the furnace comes on and works normally. I checked the vent and it is free of debris. Is it possible my new pressure switch is defective or could it be something else? Now this past summer I did accidentally spill a cup of apple juice down my living room vent, but if that was a problem then the furnace wouldn't have came on a couple weeks ago. Any help is greatly appreciated!

[hvac1000]

Look to see if the tubes running off there pressure switch are clear. Blow them out if possible to make sure there is no obstruction.

[HVACTech]

Yes I blew out the tube and nothing obstructing it. I have lived here 4 years and the furnace has ran fine. I checked the flue and nothing is blocking it either.

[tsa7man]

A pressure switch is a safety device to shut down a furnace an/or boiler if proper combustion air flow is not being provided. Which can be caused by many issues, plugged vent (exhaust and/or intake) sooted up heat exchanger surfaces /passages, usually running on LP gas, inducer slowing down due to age, pressure switch hose plugged with water, connection point of pressure switch hose plugged either at the inducer blower or on the transition / combustion box... and lastly a bad pressure switch. In your case that is not the problem, such as where you jumpered it out and the furnace ran. Disconnect the exhaust vent pipe (ONLY FOR A SHORT TEST!! ) and now see if the furnace will run... if so, the problem may be one of the following, venting plugged, condensation backing up into furnace if it is a 90% efficient unit which slows the air flow through the unit, sooted LP gas unit, or a slow inducer. You can check the inducer to see if yours has a capacitor, which could be bad, causing the motor to run slow. The correct test is to "T" into the pressure switch with a manometer to see the inches of water column that the pressure switch is really seeing, and then troubleshoot where it is sensing the air pressure, and evaluate that issue... this kind of failure / problem can be tough to check and evaluate

[biggsie]

Pressure switch , well you could have a couple of issues which could cause this code. As you have stated there could be a blockage in either the intake or the exhaust pipes. The easiest way to check for this is to undo the coupler on the intake pipe inside the furnace housing and let it draw in air from the furnace room for a couple of minutes and see if that is a fix. I have done the same with the exhaust, but only for a minute to check for a blockage(as you will create some CO while operating this way).
As you have also mentioned the drain issue sometimes causes problems. I have had to use a small piece of wire(like a coat hanger) and push through the fitting at the bottom for the collector box before, where the hose ties onto the furnace burner box. If you have a build up of condensation in the secondary heat exchanger this can cause problems. The easiest fix for this is to ensure the furnace is sitting with a slight tilt to the front(like 1/8th inch back to front), so that the condensate runs to the collector box and out into the drain. You could also check to make sure that the ventor motor is getting up to speed(just in case a bearing is getting tight and slowing it down enough to not let enough flow through to trip the pressure switch

[wmproop]

On 2 different occasions,, I found that a bird had crawled in side the plastic vent and got all the way into inducer motor housing and couldn`t get out,, had to take housing off furnace and fish black bird out,, had it blocked off,, worked fine afterwards

[T-Top]

It only takes a small restriction on the exhaust or intake to keep the pressure switch from closing. But yet the furnace will seem to burn fine with the switch bypassed. Remove the intake pipe on the burner collector box and try it, if it will not burn remove the exhaust from the inducer housing if it will not burn you have a restriction on the condensation side of the unit(hoses,drain,collector box) or a bad secondary heat exchanger.

[crash10179]

I know this is an old post but I managed to fix my furnace at 2:00 am Christmas morning following the suggestions in these posts. In case anyone else has runs into this problem check ALL the vacuum hoses. After trying just about everything listed above I found the vacuum hose connected to the powered exhaust vent housing was plugged.

[Ashurz]

Hopefully one one these suggestions work. Just like crash, it is Christmas morning, and it getting kind of chilly in the house.

[rvtweener]

on 2 differant occassions,,,I found that a bird had crawled in side the plastic vent and got all the way into inducer motor housing and couldn`t get out,,,had to take housing off furnace and fish black bird out,,,,had it blocked off,,,worked fine afterwards

I have a new product that keeps birds and debris from going down your funace vents and it will not freeze up in the winter. I have used it for 2 years now and it works awesome. There is a web site for it it is Home Page give it a try .