Tempstar Flame sensor Problems

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Old 11-23-10, 08:38 AM
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Tempstar Flame sensor Problems

My condensing Tempstar furnace will not keep lit. I replaced the Flame Sensor to no avail. I then cleaned all of the terminals, burners, etc. Checked that all of the grounds were clean and bright. Made sure the sensor was present in the flame. Checked the overtemp, and differential pressure switches.

How can I tell if the Module needs replaced? The furnace lights fine, after the blower starts, and then immediately shuts down just as if the flame sensor didn't work.

Not sure where to go from here.
 
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Old 11-23-10, 10:32 AM
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What's the model number of the furnace, which you will find on the rating plate in the burner compartment of the furnace?
 
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Old 11-23-10, 11:05 AM
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NUGS075BG02 I checked the 24 volts to the gas valve and it is there and the furnace lights. After about a 3-4 sec delay the gas valve opens and the 24 volts from the module goes off at the same time. I am thinking I should go ahead and order a new module beofre it gets to cold here (WI) I just don't want to replace parts until it's fixed. PS thanks for the reply
 
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Old 11-23-10, 06:29 PM
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What you are describing is often an indication of a pressure switch either opening when it should be closed or closing when it should be open. Rarely is the problem with the switch itself but often in the vent system or condensate drain if the furnace is 90% efficient or greater.
 
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Old 11-23-10, 08:27 PM
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Unfortunately, I can't find any manual on your furnace on line.


Is the main burner lit by a hot surface ignitor?

What is the make and model of the module?

It's premature to replace the module, and no more likely to solve the problem than replacing the flame sensor at this point.

You need to carefully observe the sequence of events that happen once the thermostat calls for heat. You may need to repeat the ignition sequence several times until you can accurately describe what you are seeing so you can describe it here.

I'm afraid the limited description you have provided so far isn't clear enough to understand what is happening or what may be wrong.
 
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Old 11-23-10, 09:21 PM
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http://icpindexing.toddsit.com/docum...4108200100.pdf

Could the model number be NUG5?




 
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Old 11-23-10, 10:09 PM
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Houston,


That's a definite help. It seems there are several different ignition systems that can be installed on the furnace though.

Since Bob refers to what is apparently a separate module, that implies it's probably and S8600 series intermittent pilot ignition, but perhaps I'm reading too much into that. Could be a Smartvalve system too.
 
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Old 11-24-10, 10:24 AM
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sequence of events

Here is the info everyone asked for:

It is definately a Furnace Model NUGS075BG02 Natural gas
the Module # is 50F47-060

The sequence is as follows:
1. Turn Power on
2. Exhaust fan starts
3. Red indicator on control module flashes once
4. I am pretty sure the main fan control relay clicks on
5. The Ignitor starts to glow
It glows for approx. 14 sec.
6. The main gas valve opens
7. The main burner lights
8. The main burner remains lit for approx. 3 sec.
9. The main burner goes out
10. The furnace times for approx one minute and then tries to restart
11. The sequence starts at #5 and repeats thru #10 twice and then the Module locks out and the red indicator starts to flash on and off continiously.

I checked the main pressure differential switch, and it closes when the blower comes on and does not open during shutdown. I also removed the hose from the main pressure differential switch and the module would not allow the igniter or gas to come on. I also made sure the vent and air intake ouside were not blocked or plugged in any way.

I checked position of the flame sensor and made sure it was in contact with the blue flame when the furnace was lit. Every once in a whole the furnace will light normally, and then the main blower comes on as it should. I also reterminated the ground at the burner with a new lug just in case it was a bad connection.

Again, Thanks for everyones help. Bob
 
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Old 11-24-10, 10:58 AM
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Now that's a model description of the ignition sequence!


Disconnect the wire from the flame sensor and measure the AC voltage between the wire and chassis ground when the inducer motor is on.


Some circuit boards would supply 24 VAC to that wire, some 120VAC.

No voltage---- replace the circuit board.


Connect your multimeter between the flame sensor and the flame sensor wire. When the burners are lit and the flames engulfing the flame sensor, measure the DC microamps (not milliamps).

Report that measurement here.

Based on your description, it is likely that the circuit board is bad. These tests are the proper way to verify that.
 
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Old 11-24-10, 03:47 PM
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No Voltage

Well, you guessed it, there is less than 1 volt present before and during and after the flame tries lighting. I went to a local HVAC place here in town and ordered a new Module. I will let you know how much it is and whether it works as soon as I get it. Thanks again for your help!:

Bob
 
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