CARRIER furnace on then off

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  #41  
Old 01-18-08, 11:53 AM
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hummmm...
sounds too good to be true, but then again, maybe is your lucky day

If it is indeed the limit switch the one that was causing the trouble, its contacts probably were closing 'by coincidence" at the same time you were shaking it. The limit switch on your unit is of the Automatic Reset type...it will close all by itself (automatically) once it cools off sufficiently.

The flame rollouts on your unit are of the manual reset type.

At any rate, let's say that it was indeed a limit switch problem. You need to find out why, else it may happen again. Have you replaced your air filter recently? dirty filters cause limit switches to trip and turn the furnace OFF.
 
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  #42  
Old 01-18-08, 12:11 PM
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Originally Posted by pflor View Post
hummmm...
sounds too good to be true, but then again, maybe is your lucky day

If it is indeed the limit switch the one that was causing the trouble, its contacts probably were closing 'by coincidence" at the same time you were shaking it. The limit switch on your unit is of the Automatic Reset type...it will close all by itself (automatically) once it cools off sufficiently.

The flame rollouts on your unit are of the manual reset type.

At any rate, let's say that it was indeed a limit switch problem. You need to find out why, else it may happen again. Have you replaced your air filter recently? dirty filters cause limit switches to trip and turn the furnace OFF.
You are absolutely right. I think it is because my air filter is dirty in the first place. That causes the overheat, then the limit switch is opened. It forced blower to cool the chamber. The limit switch, on the other hand, maybe closed by itself as you said when it is cooled (maybe it is not because I shook it) since it has been awhile.
 
  #43  
Old 01-18-08, 12:45 PM
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okey dokey
We're on the same page now. Good luck and don't forget to replace that filter....
 
  #44  
Old 01-18-08, 05:38 PM
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Originally Posted by benben View Post
I did notice that the igniter lights up but not start to burn the very first time. However it did the 2nd time. Is that a problem of my pressure switch?
Easy enough test with a voltmeter: If the pressure switch were at fault (or even something upstream of it), the outgoing 24 wire that goes into the ignition control from the pressure switch would not be carrying 24 volts.

When you catch this in the act, when it does not ignite when it should , quickly remove the outgoing 24 volt wire leaving the pressure switch that then goes to the ignition control, and quickly put test lead of volmeter (set to the appropriate A/C volt setting on your meter), and touch one lead to the spade connector on the pressure switch and the other test lead to any good metal on the furnace. If you DO have 24 Volts, then you most likely have completion of current through the limit as well as pressure switch. If you do NOT have current off that spade connector, then see if you have it on the INcoming wire on the pressure switch. (keeping in mind to leave that OUTgoing wire off the spade connector while doing both these tests.)

I did this very test tonight on a furnace. It was only after removing the OUTgoing pressure switch wire, as mentioned, that I eliminated a fooling backfeed, and found I was NOT getting power through the pressure switch. BUT, it turns out I was not even getting power INTO the pressure switch either. The wire feeding the pressure switch came from the high limit which was cutting out. So, if THAT cuts out, no power to the pressure switch and then no power to the ignition control, and hence no flame.
 
  #45  
Old 01-28-08, 06:07 AM
Join Date: Jan 2008
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Similar issue

I have a carrier unit that is running for about 5 Min. and then shuts off and recycles. Being that it is running for 5 min. I have tried the resets and even searched for a flame sensor but can not find one on this unit. I thought that the pressure switch might be losing pressure to it but it works to start up the unit. The system was working fine until last week.
Any Ideas
 
  #46  
Old 01-28-08, 07:16 AM
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special,

What type of ignition does your furnace use? And how do you know your pressure switch is working in it's entirety, because if the draft inducer starts up, this does not confirm the pressure switch is totally working. After the DIM (draft inducer motor) starts up, a seperate set of contacts in the pressure switch has to close, confirming proper draft, for the ignition process to begin. Or - DO you get to the ignition stage?
 
  #47  
Old 02-01-08, 02:49 PM
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Thumbs up

Originally Posted by pflor View Post


You've need to push the little red push button the red arrow is pointing at.
THANK YOU! THANK YOU! THANK YOU!

My wife & kids are now warm, I look like a mechanical genius, and I didn't have to fork out money for a service call. All for the cost of a couple of hours to figure out kind of what was wrong, do some Google searching, and finding your post.

I'd look even smarter if I would have remembered to change the filter. Ah, well, Yahoo! Calender should send me email reminders now.

Thanks again!
 
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