Goodman pressure switch

bus_driverOctober 31, 2012

In my twilight years, I still try to learn a little every day. Today a Goodman gas furnace less than 2 years old failed to work. It was doing nothing when I got there. I checked the gas and electric supply, all OK. No codes flashing. The 24 volt transformer had the proper output voltage. That was the limit of my knowledge. So I turned off the electricity and called a fellow who installs Goodman. He said that when turned the power back on, the code appeared-- 3 flashes-- bad pressure switch. None in stock locally. Supposedly available tomorrow.

Searching on the computer turns up several posts about this pressure switch. As I have pieced together a supposed understanding, the switch must be open at the moment the inducer fan starts and then it must close-- with every furnace cycle. The furnace will try this cycle 3 times and then shut down. Turning off the power supply and then on again resets the process.

Is this correct?

Seems to me, my idea, not suggested by others, that a simple single pole toggle switch could be substituted for the pressure switch to test the furnace for operation-- to see if all else is OK. The toggle switch would be open and then would be manually closed as the inducer fan gets up to speed. That would run the furnace for one cycle. Is this idea correct?

Do these pressure switches have high failure rates? Would it be wise to have a spare on hand?

The switch is marked 0.7 and the tech tested the pressure on the hose with the fan running and it was about 1.7, over twice the minimum required. Or is the 0.7 a maximum and the 1.7 points to some fault?

Answers for the questions are welcomed and appreciated along with additional suggestions. Those occupants will be cold until tomorrow.

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Additionally, this is a downflow furnace, not condensing.
Accessing the control board for replacing it on this furnace would be quite a task.

    Bookmark   October 31, 2012 at 7:00PM
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The original switch was made in Costa Rica. Do not remember seeing any manufactured products from there.
And perhaps the pressures involved are less than atmospheric-- vacuum. That would make more sense with the higher reading that we saw. The tech did not say anything the pressure except the raw number.

    Bookmark   October 31, 2012 at 8:53PM
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Hopefully some of the pros in the HVAC business will offer more insight on this topic.
The furnace is now working. The switch is replaced. The old one apparently has a leaking diaphragm, which I hope to test soon. The new part looks a little different, indicating that perhaps it was redesigned. To save cost-- or to improve reliability-- anyone's guess. The ones offered on eBay show what I believe to be date codes showing 2010 and serial numbers lower than the one that failed here. The photos on eBay could be copied or could be the actual item.
The contractor told me the switch was under warranty, but that the wholesaler charged $25 for warranty paperwork. He was on site about 45 minutes for the initial diagnosis one day and about 30 minutes for installation on the following day. Told me he was charging for two service calls, a total of $235. Ouch!
I decided to get a spare ignitor and have it at the ready. Turns out that this ignitor is quite a bit higher than most. Special shape and mount. Are Goodman parts typically more expensive?

    Bookmark   November 2, 2012 at 10:13AM
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Depending on where the little rubber hose attaches to the draft inducer indicates if its positive or negative pressure switch. Most likely its positive. What i do is pull the hose off the inducer, reset the door switch,turn the heat on and then blow into the hose. You should hear the micro switches "click" when you blow in and when you stop blowing, you should hear a second click. If you keep blowing while turned to heat, you will finally get ignition of the burners. This tells you the heating system is working and your problem might be a restriction in the flue pipe or some crap in the housing of the inducer where the hose connects to it. In your case, it was just a bad pressure switch.

    Bookmark   November 5, 2012 at 10:16PM
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