Blower will not shut off

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  #1  
Old 02-14-05, 05:10 PM
kcabpilot
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Blower will not shut off

This is a Carrier FAU model 58DRC045-CB and my problem is that the blower will not shut off. I've had this problem before and it was a bad limit switch on the vent plate above the burners. I'm not a HVAC guy but I'm an Avionics Tech so I know electrical and circuits. Here's what I've found so far:

I've got 24 vac coming out of the transformer secondary
It then goes through the limit circuit switches and fuse okay and ends up at the 'R' terminal.
From there it goes through the thermostat and comes back to the 'W' terminal

Here's where I get messed up because I'm not sure what's supposed to be coming back from the thermostat. According to the schematic the signal from the 'W' terminal goes to the gas valve, the pilot igniter and then back up to the time delay circuit that should energize the heating fan relay to turn the blower OFF. If I disconnect the gas valve and ignitor and jumper the two pins to the ignitor I get 12 vac at terminal 'W'. Otherwise I get nothing.

Other info: I've replaced the thermostat. The heater works fine, the pilot lights, the burners light and turn off when the temp is reached or if switched off at the thermostat.

But the blower will not shut off.

So, any ideas? I guess the next step is the circuit card but that's probably gonna cost an arm and a leg.
 
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  #2  
Old 02-14-05, 05:13 PM
M
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Does this furnace have a 3 wire pilot and a 5 wire valve??
 
  #3  
Old 02-14-05, 05:54 PM
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kcabpilot

Disconnect the stat. Blower shut off? If yes, jump r & w. Does furnace fire up? If yes, allow fan to come on then remove jumper. Does fan shut down in a few minutes? If yes, stat is problem.
 
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Old 02-14-05, 07:48 PM
kcabpilot
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mbk3, yes, 3 wires to pilot and 5 terminals on the valve.

Grady, pardon my ignorance but - what's the 'stat'? I jumpered the red and white and the burners light up. After I remove the jumper the burners go off but the blower keeps running. I know it should shut off after a delay of a minute or two - it doesn't. The blower runs all the time as soon as I push the door switch. It runs even with the thermostat completely removed.

just realized that by 'stat' you mean thermostat. I've already replaced it with a new one. No help.
 

Last edited by kcabpilot; 02-14-05 at 07:59 PM.
  #5  
Old 02-14-05, 09:59 PM
M
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4 items make fan run continuosly in Carrier products
1-bad transformer
2-open limit/roll-out switch
3-open fuse link
4-bad board
Since you can run furnace thru cycle that leaves only # 4. Sounds like stuck fan relay on board.

"stat" = thermostat
When you jumped red & white did you remove t'stat from circuit??
 
  #6  
Old 02-15-05, 06:18 PM
kcabpilot
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Hey, thanks for the help guys. I've had the board out and checked most of the components on it. Both relays work fine (not stuck or burnt) All of the capacitors, resistors and diodes appear to be fine as well so that pretty much leaves me with one culprit - the CA3098E chip on the board which performs the time delay/relay control function. With a Google search I was able to find the datasheet on it here:

http://www.alldatasheet.co.kr/datash...L/CA3098E.html

I should be able to get one for about $8. Wish me luck. I'll post here if I get the thing working.

Thanks again
 
  #7  
Old 02-15-05, 06:38 PM
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kcabpilot

Just for kicks & maybe to save you $8 & a little work, I have one more thing I'd like you to try if you will. Make sure the thermostat is set to "off" & the fan switch on it is set to "auto". Better yet, disconnect it, making sure all bare ends are separated. Disconnect the thermostat wires at the furnace & see if you have continuity between the wire which was connected to the "R" terminal & whatever color was hooked to the "G" terminal (usually green). If you do, there's your trouble. Sometimes it's the simple things that will drive you crazy.
 
  #8  
Old 02-17-05, 10:29 AM
kcabpilot
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No continuity between the red and green wires. If it helps this discussion here is a copy of the schematic.

http://home.comcast.net/~kcabpilot/f..._schematic.jpg

What I can tell you is that I DO NOT have any signal voltage at the GAS 3 terminal. Seems to me that would be required to energize the HFR and turn the blower OFF. Unless I'm reading it wrong.

Anyway, I haven't checked yet but may not be able to get a CA3098 as they are obsolete.
 
  #9  
Old 02-17-05, 11:26 AM
tcwarren1
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Similar thing happened w/ me recently...I found out it was a simple reset button on the top of my furnace...
 
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