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1001miles 10-19-2008 07:29 PM

Pressure switch stuck open? 2 areas im looking @
Hi, I've been searching for a few days & am unable to find what I'm looking for.

I have a 7 year old furnace. lennox ultra 5 advantage.

Went to turn on heat & nothing!!

The led trouble code is 3 blinks = "Pressure switch stuck open 30 seconds or longer after call for heat. on/off switch in "off" position during call for heat will generate this code ( this is right out of the furnace manual)

After researching I believe it is one of two items:

1. Draft inducer fan is bad.

2. Pressure switch is bad.

I cannot tell if the Draft inducer fan is actually spinning. I can hear the fan unit "hum" & it is very hot to the touch. However I am unsure if the fan is actually spinning!

I tested for continuity (w/ohms) from the black - green & white-green wires & found no continuity on both. There was continuity from black to white.

I am wondering how else I can test the fan to see if its working?

2. The tubes don't appear to be cloggeed, I blew in the one coming off the inducer fan & i can audibly hear the pressure switch clicking. Not sure how to test the switch with an meter.

Any thoughts / tips would be great. I'd like to try & figure this out without having to call in the repair man [IMG]http://www.********************//images/smilies/frown.gif[/IMG]


biggles 10-20-2008 07:25 AM

if the motor is hot to the touch it might be locked up with power going to it...seems the pressure switch is doing its job not bringing on the gas.with power up and meter on the 2 wires on the switch if it is open you will get a reading,if closed you get no reading except each terminal to ground.shut the furnace and try to free spin the IDM squirrel cage CW?CCW might break it quick check the circuit for the burner do a jump on the pressure switch with a short jumper for 2 seconds you should heae the spark kick in this proves the switch is waiting on the air pressure from that locked up IDM.Caution can't run the furnace without the IDM running

dac122 10-20-2008 09:46 AM

First verify your inducer is running. Its usually the first thing in the ignition sequence. If 90+ AFUE furnace go check the exhaust pipe for an obvious draft coming off. If < 90+ AFUE (ie in the 80) remove the exhaust duct and verify draft. If she's not spinning, remove the inducer and see if it will free wheel. The inducer could be jammed, blocked, have dead spot on motor, etc. The inducer must spin or else nothing works.

1001miles 10-20-2008 05:39 PM

k so i tested the inducer while it was humming (while furnace was trying to begin startup process.

White to ground .6 amps

Black to ground 120 amps.

So I believe the fan is the culprit. Are you sometimes able to clean/lube it?

Hate to ask but what is ccw?

Thanks for all the insight guy/gals! :)

DangerMouse 10-20-2008 06:03 PM

that would be volts not amps, sounds to me like the motor is toasted too, (hum/heat) but i'd tear into it to check for sure if it were me, those suckers can be expensive. and ccw=counter clock wise. =o)


1001miles 10-20-2008 06:56 PM

soooo never guess what I found when I took out my draft inducer?

2 dead birds were stuck in it & the pvc tube!!!

Everything now works like a charm -

Thanks for helping guys!!

duh --- ccw lol

dac122 10-21-2008 07:21 AM

Glad you found it.

Seems like kids, animals and pests are sworn enemies of thos PVC pipes.

malim 12-15-2008 10:57 AM

Hey All. Just wanted to say thanks for the info.

I had the same problem and learned a little bit about furnances through my adventure :thumbup:

My motor was humming but did not seem to turn. So me and my dad suspected the motor and took it apart. It was definitly stuck. What happened was 5 of the plastic blades broke inside the motor for a reason that is unknown to us. We cleaned them out and put the motor back in and started the furnance. The motor was rattling like crazy. What happened was the blade assembly was now out of balance and was knocking on the walls of the motor assembly causing this crazy rattling. However the furnance still did not work.

We thought maybe we had two problems here and it being the pressure switch. We blew in it and it seemed fine (pop open and close). I even used a multimeter to test it and if it making a contact and it did.

So the pressure switch was not the problem.:whistling2:
We decided to bypass it and stuck a wire between the two wires going into the switch. What this does is basically makes the furnance think that the pressure switch is working, but now we had another error "pressure switch stuck closed". What i figured was that the furnance when turned on checkes the pressure switch and if it is closed (default is open) right away gives you the error code, so it doesn't get to the blower motor stage.

What we did then was turn on the furnance and then a 1 sec later connect the two wires. TADAA!! It worked. We heat up our home because we didn't want to freeze, but then the motor just gave up and was stuck.

I went out today and bought a new motor.:whistling2: WOW they are over priced here in Toronto. Ridicoulous prices... some people want $475 plus tax for it.
I searched around and i was given a company that sells motor by a nice guy i called while looking for the motor.
The company is called Canada Motors. Great guys.

Canada Motor & Supply Co Ltd- more info
6 Bramsteele Road, Brampton, ON L6W 1B3, Canada‎-
(905) 451-4474‎

Popped it in and YAY. We are warm.

Thanks everybody. Great experience. Hope i did not bore anyone here, but i just felt like giving back to the community and share my experience. If you fixed something, post it here :))


dac122 12-15-2008 11:05 AM

Glad we could help to get you on the right path. It sounds like with the missing/broken blades weren't pulling enough draft to close the pressure switch. If you had a vacuum pump you could have pull the hose from draft inducer, put it on the pump and pulled vacuum at the right time to fake-out the controller.

Just curious did you have to spend the $475, or did you get a better deal at Canada Motor?

malim 12-15-2008 11:10 AM

Yeah, i had the same theory about fan not having enough power but forgot to write that.

I did get a better deal. It was $275 with tax. Not bad comparing to $475 before tax.
Make sure you ask about warranty. It seems to me these fans are very unreliable. The one that i took out was FASCO (my old one) so i figured it was replaced once already or do YORK install FASCO from the factory ?

beenthere 12-15-2008 04:35 PM

Yep, York uses Fasco's.

Many are made by fasco.

grimace15 10-23-2010 07:57 PM

I fixed my 3 bleep light this way...
I tried cleaning off the thermal sensor to no avail. The system would still come on, the pressure fan would blow, the igniter would glow, then the gas would start and light, then it would go out after 5 to 10 seconds, then the blower would turn.

Then I see that the 3 flashes indicates that the pressure switch is open. Ok...let me remove the tubing and see what I see. The side that conects to the fan part (not the switch) was a little clogged with rust like deposits. I thought it was supposed to look like that so I place the other end of the tube on the switch and inhaled and heard the switch...well...switch. hehe.

Let me look for dead birds first in the vent, becuase I was hesitant to remove the "rust" deposits from the other end. After removing two sheet metal screws, there were no blockages (no birds). Ok...since I have it off, I verifed the rat cage inside the exahust was turning both without the power and with and it did.

Now let me see if I can suck on the end of the tube from the switch long enough for it to fire up and have the blower start and keep it running. I was able to accomplish this by placing a straw in the end of the tube and sucking on it to close the switch and it FRIGGIN WORKED!

Now for that rust thing I wanted to remove. I got a small screwdirver and stuck it in the hole and all it was, was a little corrosion build up. IT WAS BLOCKING THE AIR FLOW! Now I took the other end of the tube connected to the switch and connected it to the fan and VIOLA! IT WORKS NOW.

Mind you, this is AFTER having a professional come out and tell me I needed a new control board. I had it fixed in less than two hours after he left the door. I am not paying for the visit as he could have done the same thing. Hell, I am just a pharmacist and thinking of opening up an HVAC training school!

I am seething...trying to cool off (no pun intended as we now have heat). Good thing the place is closed. They will get an earfull tomorrow...:censored:

aka Joe

kenmac 10-23-2010 10:33 PM

those small ports will clog with rust caused by condensation sometimes

beenthere 10-24-2010 03:31 AM

There are some techs that have no idea how a furnace really works. Guess you got one of them.

AlphaM1 10-30-2010 12:44 PM

thakks for saving me $?00.00

Originally Posted by kenmac (Post 522097)
those small ports will clog with rust caused by condensation sometimes

cant believe this was so easy. it took me longer to find this forum, than to fix my furnace.

just wanted to say thank you. and keep on posting, you dont always just help one person with knowledge, i can tell you, this site and the members are great. THANK YOU ALL!!!!!
:thumbup::thumbup::thumbup::thumbup::thumbup::thum bup::thumbup::thumbup::thumbup::thumbup::thumbup:: thumbup:

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