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BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22092
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have an Armstrong Air (m/n: g1d91au100d16c-1) furnace. I

Customer Question

I have an Armstrong Air (m/n: g1d91au100d16c-1) furnace. I am getting 3 blinks, pressure switch open and should be closed. I have attempted several trouble shooting techniques and am able to get it to run, but not with the appropriate configuration.
1) If I bypass the pressure switch everything is fine.
2) If remove the exhaust vent (with pressure switch connected) it will run. I have only done this briefly because I am worried about the exhaust.
With everything connected as normal
1) Ocassionally it will fire up and run for a while then shutoff.
2) Usually it tries igniting 3-4 times and never fires up.
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.

hello,

the tube on the pressure switch runs to a fitting on the furnace..pull the tube and poke that fitting clear with a drill bit or paperclip all the way through. Check tube for cracks or bad seal.

Use shop vacuum to clean exhaust pipe....let me know result

Customer: replied 1 year ago.
I used a paperclip to clear the fittings. All seemed unobstructed. All the hoses are in good shape. All fittings except one seem very tight. The connection to the inducer seems a little loose. The fitting is not barbed. Can I just trim the hose and slide it back on? It seems like it is a little stretched out.I have not run the shop vac yet, the furnace started up so I am going to let it run a while (hopefully).Prior to contacting you, I did disconnect the vent and intake. They seemed clear, but since they run through the chimney with a bend I cannot see all the way through from the furnace or the roof.
Expert:  BillyHvac replied 1 year ago.

trim the tube...make sure air tight. we need the air flow created by the exhaust fan to close the switch through the small tube

Expert:  BillyHvac replied 1 year ago.

99% of the time the intake has something in it since it draws air

Customer: replied 1 year ago.
The furnace ran for about 25 minutes before until it reached the desired temperature.
When the next call to heat came, it tries four times and never fired up.I shop vaced exhaust and intake. Seems clear.
I put a small hose clamp on the inducer hose connection.
When the next call to heat came, it tries four times and never fired up.Could this have something to do with the condensate pump? I lifted up the pump and there was some pretty nasty (maybe algae) water in there. I emptied the tray and the next call to heat succeeded. However, the next call to heat failed after 4 attempts.
Expert:  BillyHvac replied 1 year ago.

did you shop vac the drain from furnace to purge all old condensate out?

Customer: replied 1 year ago.
I only shop vaced the exhaust and intake. I am not really familiar with the drain. I will need some direction on trouble shooting the drain system.
Expert:  BillyHvac replied 1 year ago.

there is a tube from furnace that drops to the pump...just apply as much suction as you can directly to that tube...

Customer: replied 1 year ago.
This is what I see as far as drains...
1) a flexible plastic tube from inducer to 1.5" pvc trap, then pvc to a T fitting, then pvc to condensate pump
2) 1.5" pvc from something (maybe plennum, the duct work immediately above the furnace) to the T fitting
3) 1.5 pvc from humidifier to the T fittingI opened the humidifier and the "filter" is very crusty with white deposits. I took the "filter" out and turned off the humidifier and the furnace fired up.I will attempt to clean the drain pipes, but it seems that it will be somewhat difficult because there is not much clearance around the rigid pvc piping. There seems to be some kind of clean above the T fitting. I guess I will plug the actual pvc drain then shop vac from the clean out.
Customer: replied 1 year ago.
Sorry...I think the pvc is 3/4" not 1.5". The computer is upstairs and furnace is downstairs. Argh, I've been getting my exercise today.
Expert:  BillyHvac replied 1 year ago.

has the furnace been running more reliably?

Customer: replied 1 year ago.
I had to leave the house for a couple hours.
I blew and vaced the drain from the inducer to condensate pump.
It seems to pretty reliably start up on the fourth ignite attempt. I still think it's not quite right.
The drain lines do not seem clogged, but they are pretty dirty.
Do you think I should try cleaning them? I especially wonder about the drain line coming out of the heat exchanger. I don't think that one really got vaced, only the inducer lines. I will have to disconnect the rigid pvc to get at the heat exchanger line.
Expert:  BillyHvac replied 1 year ago.

the line from the exchanger is main line.

When it is pressure switch fail we need to make sure:

Both exhaust and intake pipe are clear

Drain is clear

pressure switch tube is secure and tight

tube fitting is clear

If all of that is in order...there is always a chance we simply have a weak pressure switch.

Customer: replied 1 year ago.
Ok. Then I will work to ensure both of the drains (from inducer and exchanger) are completely clear.
The furnace should kick on with the first attempt. Right?
Expert:  BillyHvac replied 1 year ago.

correct...if not..the pressure switch is worn and needs replaced.

Billy

Customer: replied 1 year ago.
Last evening I clean the drain from inducer to trap, and cleaned the trap assembly. I watched the furnace cycle three times, every time it fired on the first try.
Overnight it stop working, I get three flashes again.
In the morning I power off and on the furnace, it started on the fourth attempt. Ran for about ten minutes the stopped with a one flash code (failed to ignite). I power off and on again, it started on the second attempt and ran for about 20-25 minutes until the desired temperature was attained.After I cleaned the drain tube and trap, I filled the trap with water. The water can be seen going about 1" up into the drain tube from the trap. When the inducer starts, that water disappears into the trap (or beyond). Is that normal?
Expert:  BillyHvac replied 1 year ago.

the trap is there to prevent air exchange thus holding water in the furnace...the trap will "move" when the inducer kicks on...

Sounds like you nee a new switch.

Expert:  HVAC Guru replied 1 year ago.

The water in the trap is normal and should disappear when started, that is working as it should to answer your question.

We are on the honor system for our time, all I ask is please rate my service using the STAR RATING LINK on your page before you leave. If you are not happy with the service please let me know before leaving a negative rating. This is the only way I am paid or credited through the site for my time. This will also allow you to get directly back to me for FREE follow up questions and tips are greatly appreciated! Thanks

Customer: replied 1 year ago.
I am hesitant to replace the pressure switch. My fear being there is something else going on and the pressure switch is trying to tell me.
The furnace has been running pretty reliably. I would say maybe once a day it will error out, but then it will pick back up after the lockout. It still is not reliably starting on the first ignition attempt.
Here is what I am wondering...
1) How can I be sure the pressure switch is failing?
2) Could the inducer be starting to fail? Do they degrade, or do they just fail immediately?
3) Are there portions of the system that I have not been able to clean? I am wondering if I should remove the inducer to access components behind it to clean.
Expert:  HVAC Guru replied 1 year ago.

Yes I would agree if you remove the pressure tube from the pressure switch lick you finger and seal the tub on that end and start the unit when the inducer starts up do you feel suction on the tube if you remove your finger and put it back on there should be some suction there.

Customer: replied 1 year ago.
There is suction, but it is not very strong.
Expert:  BillyHvac replied 1 year ago.

Have you purged with the shop vacuum? (important)

Have you tried running with the intake pipe removed If 2 pipes present..one is exhaust and one is intake) to make sure no pipe blockage?

Did you clean out the fitting the tube attaches to on furnace?

Customer: replied 1 year ago.
To recap...
* There is no blockage.
* I have shop vaced everything.
* I have cleaned all the fitting with a paperclip.
* I cleaned the tube from the inducer to the pressure switch.
* The furnace is working 75% percent of the time.
* You were thinking the pressure switch needs to be replaced, but I am hesitant because I have a couple of pending questions.Here is what I am wondering...
1) How can I be sure the pressure switch is failing?
2) Could the inducer be starting to fail? Do they degrade, or do they just fail immediately?
3) Are there portions of the system that I have not been able to clean? I am wondering if I should remove the inducer to access components behind it to clean.
Expert:  BillyHvac replied 1 year ago.

The shop vacuum to furnace should purge everything.

I know you want to find out before buying a switch...but without air testing manometer for pressure through the system, amp draw of motor it is hunt and clean.

You can pull the draft motor and check...but eventually you buy switch or invest in a manometer to test pressure at the pressure switch

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