What is this part?

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  #1  
Old 11-06-11, 05:21 PM
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What is this part?

Hi Everyone,

So I've been having fun troubleshooting my furnace. I've fixed my own appliances, but this is my first shot at a furnace. It's a Carrier
58SXA080 gas furnace.

Here's what started to happen: the thermostat would turn on to call
for heat. The pump that clears the gas from the exchanger starts
and run like normal. But then either shuts down, or just keeps on
running. So I figured that the switch that gets triggered once
pressure builds up is not working. When I mess with the part I
circled in the picture, I start to hear the ticking and the burner
ignites. Then the blower eventually turns on and I get heat. This
works for a day or two, then I have to repeat the procedure all over again.

So I think I need to replace the part, but what's it called.

Here's the pic:

Thanks!
 
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  #2  
Old 11-06-11, 08:25 PM
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That's the p[ressure switch, which has a single pole, double throw switch as part of it.

About 2% of the time the switch is bad.

The inducer motor should turn on and stay on as long as you have 24VAC being applied to the W Terminal. If it's shutting off when that is energized, that's a problem.

If the inducer motor powers up and the pressure switch doesn't close, you probably have something plugging up the vent pipes, drainage system or heat exchanger. It's unlikely to be a problem with the pressure switch.

Pull the PVC pipe for the air supply off the rubber boot at the inlet at the furnace and look for a leaf that might have been sucked into the pipe. Also look for any water traps in the vent pipe that might allow water to accumulate in the PVC pipe.
 
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Old 11-06-11, 08:56 PM
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Thanks for the reply. It is a leafy area where the exhaust and intake come out of the house. And there are more leaves this time of year. Birds are always building nests there too. I'll check it out tomorrow.

I also read on this forum it was suggested to pull the hoses off that pressure switch and make sure they are clear. I'll try that too.
 
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Old 11-07-11, 09:26 PM
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Tonight I checked the vent pipes. There were some old leaves and debris on the screen on top of the furnace where the vent pipe goes in. The exhaust was clear. I cleaned that out and the inducer motor starts, runs for a couple minutes and then shuts down. It works every now and then though. Seems like when I play with the pressure switch, it will work and I get heat. It will be ok for a couple days.

When the repair person took a look at it last week, this is what he wrote on the work order "found power to gas valve & to ignition module, but no power to ignition cable."

He recommended replacing the ignition module, or the furnace because he said that might not fix it. That's what lead me to do research and try and find out what's wrong with it.

Maybe a cold solder on the ignition module board? That could explain why it sometimes works. New modules are 200 bucks, so I really want to make sure that's what it is before I replace it.

And I should mention that the last couple of days when it doesn't work, the inducer motor starts, runs for a couple minutes, then I hear a click like the pressure switch closes, and then everything shuts down.

And other thoughts are appreciated...
 
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Old 11-08-11, 02:09 PM
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<<The inducer motor should turn on and stay on as long as you have 24VAC being applied to the W Terminal. If it's shutting off when that is energized, that's a problem.

>>


You are only following part of the directions you are given.
 
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Old 11-08-11, 02:16 PM
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Originally Posted by SeattlePioneer View Post
<<The inducer motor should turn on and stay on as long as you have 24VAC being applied to the W Terminal. If it's shutting off when that is energized, that's a problem.

>>


You are only following part of the directions you are given.
Not exactly, just ran out of time. I'll check it tonight. No other thoughts however on the other items I mentioned? Or you just waiting to find out about the 24 VAC?
 
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Old 11-08-11, 02:22 PM
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A furnace doesn't just turn on. It does a series of things in sequence that results in heat if everything works properly.

If things aren't working properly, you want to identify at what point in the sequence things aren't working. According to your posts the inducer motor may not be starting or operating reliably.

The inducer motor should turn on and stay on as long as the thermostat is providing 24 VAC to the W terminal.

So that's what you need to check and verify. Until you know that is working properly you can't reliably test other parts of the sequence.
 
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Old 11-08-11, 02:24 PM
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Originally Posted by SeattlePioneer View Post
A furnace doesn't just turn on. It does a series of things in sequence that results in heat if everything works properly.

If things aren't working properly, you want to identify at what point in the sequence things aren't working. According to your posts the inducer motor may not be starting or operating reliably.

The inducer motor should turn on and stay on as long as the thermostat is providing 24 VAC to the W terminal.

So that's what you need to check and verify. Until you know that is working properly you can't reliably test other parts of the sequence.
Ok, thanks. I'm on it. Luckily we are enjoying 70 degree weather this week, but I only have 1 more day before it drops to the 30's and 40's.
 
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Old 11-08-11, 04:53 PM
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Ok, so when the inducer motor starts, I get 24 VAC to the W terminal. It stays at 24 V. Then after about 2 or so minutes I hear a click in the pressure switch/ignition module area. Then the inducer shuts off, but I still have 24 VAC at the W terminal.
 
  #10  
Old 11-09-11, 06:33 AM
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It's working now. After checking for 24VAC on the W terminal, I decided to test the pressure switch. So I blew into each of the hoses with my meter attached to see if the switch was turning off/on, and it was. That led me to think that there was no pressure going to the switch. So I took off the hose coming out of the inducer (not the vent pipe) and cleaned it out. There was some old leaves and other debris in it. That hose went into a black plastic box (not sure what the actual name is). Out of that box came a smaller hose attached to the pressure switch. I could not feel air coming out of that hole, so I took a coat hanger and cleaned out where the hose attaches to the black box. Turned the furnace back on and could now feel air coming out if it. So I turned the furnace back off and put everything back together. Turned the furnace back on. The inducer started, then I heard the ticking for the ignitor, then the flame. I couple minuter the burners fired up, then blower.

So there was a blockage where the pressure switch hose comes out of that black inducer box. Obviously it's still floating around in there, so is there any way to take that apart and clean it out?

And I'm calling the heating/cooling place that sent someone over to look at it. Why isn't that one of the things they checked? It literally took me less than 5 minutes to takes the hoses off and clean everything out. Instead he recommends a new furnace??!! Ridiculous. If not for this site and the help I got on this thread, I may have given up and just got a new furnace. So thanks for your help.
 
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