Original message
| danl
 |  "Carrier MCA"
, posted Fri 15 Feb 09:21  
Yesterday I went to a customer that had a 90% carrier furnace. The condensate pump was full of water & not pumping. I took apart & cleaned. When I turned furnace back the pressure switch would not close. It sounded like water was backed up in exghaust pipe outside. I blew out trap. I couldn't take trap out cause installers glued hose to trap in the bottom. I checked nipple for blockage on inducer. I took off flue from inducer & a little water came out. Inducer would run for a couple of minutes & then pressure switch would finally close. Furnace runs ok for cycle. I turned off for about 10 minutes & same thing again. Anyone know what I can check next? Im kind of at a loss
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Replies:
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| theduke03
| "Re(1):Carrier MCA" , posted Fri 15 Feb 19:04
The sound you heard was probably air being sucked thru the dry trap that you just blew out. that should stop once it refills. You should definately check the screen at the air inlet to the burner.
You can't put a price on comfort! Be Safe.
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| bigglenn357
| "Re(1):Carrier MCA" , posted Fri 15 Feb 10:24
You shouldnt blow out those type of traps as you can ruin them.Check pitch on exhaust pipe,it should be pitched back toward furnace so condensate can run back to unit and drain
Big Glenn
"Imagination is more important than knowledge" (Albert Einstien)
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| | danl
| "Re(2):Carrier MCA" , posted Fri 15 Feb 11:00
Thanks for the reply. I think the pitch on the flue pipe is ok. The furnace is 8 yrs old & customer has never had a problem. Do you think wind could cause this? They live in the country & it is open. I'll remember that about blowing out traps
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| | tinmantu
| "Re(3):Carrier MCA" , posted Fri 15 Feb 13:47
I'm no Carrier expert, but I've seen Bryants that age that have a screen where moths and leafs will block off enough to prevent the pressure switch from making. Depending on elevation of where they live, winds and low pressure systems can cause a one time problem.
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| | JJRRIC
| "Re(4):Carrier MCA" , posted Fri 15 Feb 16:28
There is no condensate pump. Check intake screen for blockage. Check w/ menometer for proper vent differencial. shbe around 2.5 in. of water col. Condensate trap has two drain ports inside assembly. Blow out both sides. Put back together and run water thruogh it to make sure no clogs in drain system. wiggle wires from pressure sw. while unit is running. If unit locks out, change sw.
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| | static
| "Re(5):Carrier MCA" , posted Fri 15 Feb 18:40
If it's got one of the older metal can pressure switches, the contacts in that little microswitch relay do tend to get weak...worth checking.
Are you sure you got all the water out of the secondary heat exchanger? Any signs that the inducer housing or collector box is leaking?
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| | danl
| "Re(6):Carrier MCA" , posted Fri 15 Feb 19:22
I haven't had to go back yet. I told customer to call if they have any more problems.
I didn't see any blockage at the screen. I'll check with magnehelic if I have to back. I went outside when the pressure switch wasn't closing & it was a gurgling sound coming out of the exghaust pipe. After a few minutes the furnace fired up & cycled good. I didn't see any signs of inducer housing or collector box leaking.
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| | marchvac
| "Re(7):Carrier MCA" , posted Fri 15 Feb 20:09
After the trap is primed and you still have a gurgle in the pipe that means that it is sagging somewhere and filling with water. Is this natural or propane.
Be careful sometimes you don't get a second chance
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| | danl
| "Re(8):Carrier MCA" , posted Fri 15 Feb 20:18
Their on propane. The plug on gas valve was stripped so I couldn't check pressure. The vent run is about 10 feet.
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| | marchvac
| "Re(9):Carrier MCA" , posted Sat 16 Feb 08:52
Has the propane tank ever run out and the furnace was trying to run. You will need to check the venting system with a manometer. Could be a plugged secondary heat exchanger.
Be careful sometimes you don't get a second chance
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| | danl
| "Re(10):Carrier MCA" , posted Sat 16 Feb 10:49
I'm not sure if their propane tank ever ran out. If I have to go back I'll check vent system with manometer. I appreciate the help. This was one of those calls that didn't feel right when I left
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