I've still got it

[ForceFed70]

I've still got it UPDATE - Furnace broke again!

Came home today to the wife saying it's cold in the house and the furnace isn't turning on. She had the thermostat cranked but it was only 60* inside

Checked the basic's (breaker, cycled power on/off, turned thermostat on/off) but nothing. Couldn't even get the fan to run in "fan only" mode. So I bust out the DMM and the tools and start pulling the access panels off. Furnace is 20 years old.

I have no HVAC repair knowledge. I went to college 12 years ago for Electronics Engineering Technology however I've been employed with computers ever since I graduated and have forgoten a lot of what I learnt.

I noted that when power was applied to the furnace nothing really happened. I could hear 1 relay "click" but that was all that would happen.

1st I checked that power was making it's way into the mainboard - OK
2nd I checked that the Transformer was working and got 27VAC according to the DMM - OK

I didn't really know where to go from there so I started studying the diagrams on the back of the service panel:
- I noticed that the relay I heard clicking was the fan relay. But the fan wasn't turning on. So I measured voltage to the blower/fan. Nothing. So I thought maybe the relay was bad. Spent a bunch of time looking at the relay and wishing it wasn't soldered to the control board only to realize that it's marked NC (Normally Closed) the clicking I heard was the contacts opening to prevent operation of the fan... so not likely the relay.
- After a bunch more poking around, I was about to give up and call a professional when I decided that it seemed like the furnace wasn't even trying to light. That made me wonder about the thermostat. I had ignored the thermostat earlier because I couldn'd even get the fan to run but decided to take another look. Then I noticed that there was no wire on the thermostat terminal for "fan only" it would never have worked. I measured voltage across the R and W terminals and it said 24V... according to the diagram this connection should be closed when the thermostat is calling for heat which would mean I should be measuring 0 volts. So I put a jumper between the terminals and powered up the furnace. VOILA... she lit up right away.

I'll pick up a new thermostat tomorrow.

A pro probably would have diagnosed this problem in just a couple of minutes, but I'm still proud of myself for figuring it out.

 

[Boiler]

Congrats, always great to figure it out yourself. That's the point where I walk into the living room, look at my 3yr old and 5yr old girls, hold whatever tool I'm carrying up into the air like it was a sword and say "Dad fixed the heat!"

Followed by their smiley reply of "Yay!"

 

[daveroy]

Don't sell yourself short.
Pros can take a long time to find stuff...

 

[rickairmedic]

Forcefed good to hear you got it figured out on your own . I had the opposit problem on a call today where if the Tstat was set to heat even with it turned down to 50* it would come on and stay running until you turned it off manually . This was also a problem with the thermostat itself .


Rick

 

[letz4wheel]

Mom had a new A/C unit installed in Florida. It was supposed to save them a ton of money lol. Ended up thier bill went from a couple hundred a month to about 900 a month. Called the install people out twice and they said "nothing wrong". They finally called a warrenty guy out...turns out when the thermostat called for A/C both the A/C and heat strips lit up....sometimes it doesn't pay to go with the cheapest :O)

 

[ForceFed70]

Wow, lots of stories about thermostat problems! I always throught that thermostats were pretty problem free.

Was a great fealing when I figured it out. Told the wife that tonight she got to sleep with the furnace repair man!

 

[ForceFed70]

Ugh. So the furnace stopped working again last night.

This time with completely different symptoms. The blower/fan was running non-stop and it wouldn't even attempt to fire.

I got smart this time and checked the troubleshooting chart. It mostly talked about some limit/safety switches, a fuseable link, and the fan relay. Seems that having the fan run 100% of the time can be some sort of a safety mode.
- Looking at the wiring diagram I noticed that the fuseable link along with the limit and safety switches were all part of one circuit loop. Instead of checking each switch and the fuseable link (not a regular fuse that you can just look at to see if it's blown) I measured the resistance across the whole loop. It measured 3ohms which meant that none of the switches or the fuse was open.
- It's not easy to check/test the fan relay bacause it's soldered to the circuit board. But it did seem to work fine when I was playing with the furnace the other day. I disconnected the wire to the blower motor and turned the furnace on/off. Sure enough, the relay wasn't "clicking" and I knew it should be because that's what it was doing on Wednesday when I was diagnosing the thermostat problem.
- Finally, I decided to check for low voltage power from the transformer as this is what is used to throw the relay.... and Nothing! On Wednesday I measured it at 27VAC, but 0VAC today.
- Checked the voltage to the primary winding, 120VAC.
- Pulled the transformer out. 1ohm resistance across the secondary windings, infinate resistance across the primary windings. The transformer has definately failed.
- Was going to plug in the electric heaters and wait until Monday to get parts then had an idea. I pirated a similar transformer out of an adjustable power supply that I made in College. It was almost the perfect match, just didn't need to use the center tap on the secondary coils.
- Wired in the new transformer and furnace is back to normal.

So, do you guys think the earlier failure and this failure are related? Could the transformer being on it's way out somehow take out the thermostat? I did see a burnt up wire in the old thermostat.

Also, I noticed that the broken transformer has a manufactured date on it of 2009! We moved into the house in June 2010. They must have just relaced this part before we bought the house. I wonder if there is something else going on that's causing the furnace to "eat up" transformers?

 

[HVAC Phil]

Ugh. So the furnace stopped working again last night.

This time with completely different symptoms. The blower/fan was running non-stop and it wouldn't even attempt to fire.

I got smart this time and checked the troubleshooting chart. It mostly talked about some limit/safety switches, a fuseable link, and the fan relay. Seems that having the fan run 100% of the time can be some sort of a safety mode.
- Looking at the wiring diagram I noticed that the fuseable link along with the limit and safety switches were all part of one circuit loop. Instead of checking each switch and the fuseable link (not a regular fuse that you can just look at to see if it's blown) I measured the resistance across the whole loop. It measured 3ohms which meant that none of the switches or the fuse was open.
- It's not easy to check/test the fan relay bacause it's soldered to the circuit board. But it did seem to work fine when I was playing with the furnace the other day. I disconnected the wire to the blower motor and turned the furnace on/off. Sure enough, the relay wasn't "clicking" and I knew it should be because that's what it was doing on Wednesday when I was diagnosing the thermostat problem.
- Finally, I decided to check for low voltage power from the transformer as this is what is used to throw the relay.... and Nothing! On Wednesday I measured it at 27VAC, but 0VAC today.
- Checked the voltage to the primary winding, 120VAC.
- Pulled the transformer out. 1ohm resistance across the secondary windings, infinate resistance across the primary windings. The transformer has definately failed.
- Was going to plug in the electric heaters and wait until Monday to get parts then had an idea. I pirated a similar transformer out of an adjustable power supply that I made in College. It was almost the perfect match, just didn't need to use the center tap on the secondary coils.
- Wired in the new transformer and furnace is back to normal.

So, do you guys think the earlier failure and this failure are related? Could the transformer being on it's way out somehow take out the thermostat? I did see a burnt up wire in the old thermostat.

Also, I noticed that the broken transformer has a manufactured date on it of 2009! We moved into the house in June 2010. They must have just relaced this part before we bought the house. I wonder if there is something else going on that's causing the furnace to "eat up" transformers?

Could have been a loose connection on t-stat that caused an excessive draw on low voltage side of system. Also could be a faulty coil in gas valve drawing higer amps than usual. What was the rating on the transformer that burnt up? 40VA?

 

[HVAC Phil]

Forcefed good to hear you got it figured out on your own . I had the opposit problem on a call today where if the Tstat was set to heat even with it turned down to 50* it would come on and stay running until you turned it off manually . This was also a problem with the thermostat itself .


Rick

Rick, i find alot of stat problems related to people buying the cheap junk from HD, Lowes, etc.

 

[rickairmedic]

Rick, i find alot of stat problems related to people buying the cheap junk from HD, Lowes, etc.

Phil thats funny and I cant agree more . The Tstat in question was a friken POS Hunter from Home Depot . I tell homeowners daily if you decide to replace your stat buy a Honeywell only dont even look at the other options as in the home stores there is only one option to look at Honeywell . The other stats they sell you might as well being home and just go ahead and smash it with a hammer as that will bring you more joy than actually hooking the POS up .


The electric only air handler ( no heat pump ) and Stat were installed by " six packers " . This job was in New Albany,In. where it seems the only code is " hopefully it wont burn down the house " when dealing with HVAC or electrical .


Rick

 

[dave67fd]

You sure you just didn't come up with that second story to "please" the wife?

 

[ForceFed70]

Could have been a loose connection on t-stat that caused an excessive draw on low voltage side of system. Also could be a faulty coil in gas valve drawing higer amps than usual. What was the rating on the transformer that burnt up? 40VA?

Yes, 40VA coil.

Furnace is still working this morning thank goodness. Although I've noticed a couple of times now where it has lit and then turned off. I think the flame sensor is on it's way out or needs a cleaning. Looks like I'll be taking it apart again.

 

[ForceFed70]

You sure you just didn't come up with that second story to "please" the wife?

I wish! I have easier tricks for that

 

[rickairmedic]

Go ahead and clean the Flame sensor now while its fresh in your mind rather than when its 5*F out and you wake up frozen .

Rick

 

[HVAC Phil]

Make sure you clean the flame sensor with steel wool and not sandpaper. Sandpaper is too aggressive and removes the zinc from the sensor.

 

[familytruckster]

It could be a bad fan motor. check if it spins freely, if you can get it to run, check how many aps it is drawing.

 

[ForceFed70]

Make sure you clean the flame sensor with steel wool and not sandpaper. Sandpaper is too aggressive and removes the zinc from the sensor.

Doh! Too late now.

The sensor isn't like I was expecting it to be. It appears to be a couple of bi-metalic strips. It didn't have a lot of buildup on it.

Alas, it appears to be worse now instead of better. But now the problem is getting the pilot to light from the electronic "sparker".

The pilot and sensor/switch seem to come as an assembly. It almost looks like it's been replaced with a different but similar assembly. It just doesn't look "right".

I wonder if the assembly is in the proper orientation for it to light properly. Does anyone know if the angle it's at is correct?

 

[Innov8tive1]

With a 20 year old furnace it might be time to have someone come and have a look at it. I have seen more than one furnace with a cracked heat exchanger blow back and either trip a blowback sensor or blow the flame away from the flame sensor thus making it "think" there is no flame and it shuts down.

 

[Full Throttle]

With a 20 year old furnace it might be time to have someone come and have a look at it. I have seen more than one furnace with a cracked heat exchanger blow back and either trip a blowback sensor or blow the flame away from the flame sensor thus making it "think" there is no flame and it shuts down.

x2, I am a HVAC service man by trade. time to call in a pro. gas and sparks make for a bad day.

I don't like DIY on gas or anything that can go boom! unless you know what your doing

 

[Innov8tive1]

I'm no HVAC guy and with a background in electronics I can troubleshoot a furnace (often quicker than an HVAC guy) but I know when it's time to call someone in who knows more about it than I do.

 

[Full Throttle]

I'm no HVAC guy and with a background in electronics I can troubleshoot a furnace (often quicker than an HVAC guy) but I know when it's time to call someone in who knows more about it than I do.

more to it than just electrical.

 

[Innov8tive1]

Hence knowing when to call someone in.