Coleman gas furnace no ignition

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  #1  
Old 12-01-10, 08:30 AM
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Coleman gas furnace no ignition

Just started today, furnace starts, I noticed no glow from ignitor. I replaced transformer last year, got 24v from that. Model 2960, fairly old unit. What should I check? I do know exhaust blower is working, causing proper draw on the diaphram deal. It is a hot surface burner ignition.
Did some further checking..theres an ignition module, from what I've read, should be 120v going to ignitor, I've got 16v AC, assuming I'm on the right plug ( 2 wire connector, white wires going into furnace just under gas valve). I put my meter on both wires, then one each with the other on gnd. anywhere from 16-12v AC. 165 ohms was the ignitor itself, does that sound right? Too high?
 

Last edited by mwpayne; 12-01-10 at 09:14 AM.
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  #2  
Old 12-01-10, 01:56 PM
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Fromw what I've been able to learn scouring the net, my UN-educated guess is the ignition module is bad. It will sit with very low AC voltage for several minutes, then there's loud click, then it goes to 24V, reading at the HSI plug. That's the flame sensor voltage, correct? However, the HSI reads 165 ohms, it should be around 40-60, is that right? This unit is 15 years old, original parts. Should I plan on replacing both, or am I completely in the wrong area? I appreciate any guidance.
 
  #3  
Old 12-01-10, 02:28 PM
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Once the thermostat calls for heat, the inducer motor should start and come up to speed.

Once that happens, the pressure switch should close. Use your multimeter to verify that 24VAC appears on both sides of the pressure switch terminals when the inducer motor is on.

The 24 VAC from the pressure switch then goes back to the ignition control, which should turn the voltage on to the hot surface ignitor.

Unless you have a Honeywell Smartvalve (which lights a pilot light) the HSI voltage should be 120 volts and the ignitor should glow white hot. After a 15-30 second HSI warmup, the gas valve should turn on and the burners should light.


Verify that the pressure switch is closing.

What is the make and model of the gas valve and ignition control?
 
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Old 12-01-10, 03:09 PM
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Wonderful. I just turned it on to do as you said, I smelled something, and smoke was coming from the 24v transformer, just as it did several months ago when I had to replace it. Now no blower, nada. Also no heat pump outside.
Maybe I better get a real tech on this one to take a look see.
 
  #5  
Old 12-01-10, 03:30 PM
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Sounds like you burned out the transformer, and probably didn't identify the cause of the short circuit last time, allowing the problem to recur.

The usual cause of a burned out low voltage transformer is a thermostat wire being shorted to ground because it is cut on some sheet metal duct work.

Inspect the whole length of the wire, or as much as you can, for cuts, defect or problems.

You can also use your multimeter to test each wire for a short circuit to the furnace chassis ground.
 
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Old 12-01-10, 03:36 PM
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Will do, and thanks for your help.
 
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