For you HVAC experts.

me ^ | 12/25/07

[LouAvul]

My furnace failed to click on this morning. The digital light code was: 1 long light; 2 short lights.

I pulled the cover off and underneath is a rocker switch. It's designed to shut off the furnace whenever the cover is off (I'm assuming).

Anyway, I pushed the rocker switch and the furnace started to come back on. I replaced the cover and the furnace is now running.

I guess I'll call a heating pro this week but, for the time being, any ideas?

[SouthTexas]

Get your book out and read the codes. It may also be on the inside of the front cover.

It is most likely a safety shutdown from either low gas pressure or dirty electricity (brown out), although your furnace may need to be cleaned. There are "lock-outs" if ignition fails three times in a row.

If it doesn't do it again, don't worry about it.

[raybbr]

Did you have a power outage?

[RDTF]

that’s a Merry Christmas wake up :^)
Glad you have the heat back.

[xcamel]

Could have been a bubble in the fuel line also - flame detect would be tripped, and just need a reset.. (if it’s an oil furnace)

[Dumpster Baby]

The codes are the most important clue. Another possibility is that the electrical switches used in everything these days are made as cheaply as possible. The switch contacts are almost always just unplated brass parts that touch together in some way. A brass contact that doesn't get cycled and "wiped" can slowly oxidize and become intermittent. Possibly a cover interlock switch momentarily opened or became intermittent due to the vibration of the furnace blower. I've seen the same thing here on wall light switches that don't get used very often. Turn a light on and it flickers. Turn the switch on and off a few times and it's OK again.

I hate low quality electrical stuff, but I understand why it exists. If a manufacturer saves a dollar in production costs on a million units, that's a million dollars they saved.

[listenhillary]

Maybe you can profit from my stupidity. My furnace was doing the same thing. I could get it to start by removing the lower door and putting it back on, but it would not start without doing this every time.

$105 to determine that while the thermostat was functioning and correct voltage was reaching the furnace, the thermostat wire to the furnace was broken and resting against the screw terminal.

Stripping the wire and re-securing it to the screw terminal was all that was needed.

[buck61]

any ideas?

I have experienced this with my heat control.

Be very careful in removing the cover. Get a soft small brush and, remove the dust from the controls.

I was explaining this problem in a hardware store, when some-one came to me and explained the dust thing. I did as he instructed and, it solved the problem.

I hope this will work for you also????

[texas booster]

Hey, we need someone with a clue over here about HvAC.

And between you and me, that someone sure isn’t me.

[bad company]

If you’ve got the time I’ve got a question. The ground wire between my house and the pole broke and everything in my house was jolted with 220v. Everything else has been replaced or fixed except the HVAC. I get nothing from it. No heat, no ac, It’s only a few years old. It’s my next project and would appreciate any help at all.

[LouAvul]

The code says: “Gas Heat Lockout. Control will NOT auto reset. Check for: Stuck gas valve relay on control or miswire to gas valve circuit.”

BTW, it’s a nine year old Carrier unit.

[cyclotic]

If it’s a 90+ efficiency they have a shutdown if there is not enough incoming air. I had that happen once. I think a plastic bag blocked the incoming air pipe. Once it shut down, the pressure released and the bag dropped.

Now, maybe you can help me with my dryer. My BIL and I were up till 12:30 last night tryeing to diagnose that. We found a broken sensor and ordered a replacement on Ebay.

[martin_fierro]

HVAC Socks

[Condor51]

*** My furnace failed to click on this morning. The digital light code was: 1 long light; 2 short lights. ***

Read your O&M Manual (Operating & Maintenance), or it may be an Installation Manual. The answer to the light code 'should be' in there. It may be something very minor (momentary low gas pressure).

That being said it could be in your Thermostat (the Light Code may point that out). Even digital stats go bad after several years.

But if its working now, don't be in a rush to call a serviceman, especially TODAY. And if you have to get one, get estimates.

Not knowing how old your furnace is, be careful of one thing under any case - if the service mans says "your heat exchanger is 'rusty' and you need a new furnace" - SHOW HIM THE DOOR.

But again, the answer lies in your manual to the light code.

(and yes, every furnace access door has a cut off safety switch behind it)

[Condor51]

Got it :-)

[MindBender26]

Go elsewhere on ‘net.

Find a site that allows you to enter your furnace manufacturer and the codes.

I did same for clothes dryer and bought $21 part. Installed it myself in about 3 minutes. Service call would have been $80, plus a $60 part, and waiting about 10 days for it!

Merry Christmas.

[Dumpster Baby]

That's a tough one. You could have a zapped thermostat (if it's the electronic type) or a blown 24V control transformer that powers the thermostat circuit. If your central unit has any kind of electronic circuit board in it, it's probably zapped.

I'll try to draw a 220V system here:

<---------------------------------240V----------------------->

L1<-------------120V--------->N<-------120V--------->L2
|____________o_______|______o_________|
|____________o_______|______o_________|

The voltage difference between L1 and L2 is 240 volts. The voltage difference between either L1 or L2 and Neutral is 120 volts. The little "o's" are 120 volt devices, like lamps, TV's, etc. When the external Neutral return is broken the 120 volt loads get connected in series from L1 to L2 and the full 240 volts gets applied to the 120 volt loads connected in series. Each 120 volt load may get more or less than 120 volts applied to it, depending on the different resistances of the various loads. The 120 volt devices that get less than 120 volts probably won't be damaged, but the ones that get more than 120 volts will be damaged by excess voltage.

The center Neutral return prevents either 120 volt side from going any higher in voltage. When the center Neutral is lifted from earth ground by a broken wire, the 120 volt devices on either side end up connected in series between L1 and L2.

An older central unit like mine with no electronics in it shouldn't be damaged, but I guess most of the more modern stuff has electronics in it.

It will probably take an A/C guy to troubleshoot the unit to find out if it's simply a bad 24 volt control transformer or a zapped electronic circuit board somewhere.

Hope this helps a little.

[bad company]

Its a really base model. Here's the thermostat; I didn't see any fancy circuit boards in he main unit downstairs. IIRC it was a voltage transformer that got smoked in the dishwasher from this incident. Unless you advise me otherwise I'm going to hunt down the control transformer and use the home depot gift card I got today and give it a whirl. Even if that doesn't fix it, it stands to reason that it got hurt from the overcharge and would prolly die at another point.

[Dumpster Baby]

That thermostat is purely electro-mechanical, and pretty much immune to voltage. There will be a small 24 volt transformer somewhere that supplies power to it. It might be mounted inside the central unit or it might be mounted near the main breaker panel for the house. I have 2 of these transformers near my breaker panel - one for the thermostat and one for the doorbell. Hope this helps.

[bad company]

Thanks a bunch. I think I know right where it is. Your reference to the doorbell gave it to me. I really appreciate the help.