induction motor runs but no burner ignition


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Old 01-22-09, 11:52 PM
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induction motor runs but no burner ignition

I have a Goodman forced air natural gas furnace, model # GVPS050-2 with a Ritetemp model # 6022 programmable thermostat. The unit was manufactured around 1992. When I set the t-stat to HEAT and fan to AUTO and set the temp to @75, the inducer motor kicks on but the burners will not ignite. The induction motor turns on and off properly as I change the temp setting on the t-stat. I can set the t-stat fan to ON and the blower motor comes on properly. I suspected the thermocoupler was the culprit so I replaced it. No change in condition was noted. My next guess would be the gas valve (model # 36C03, Type 205, part # B12826-05) but I think it is foolish and wasteful to just keep throwing parts at the furnace until I get it right. As the burners were rusted and beginning to deteriorate, I replaced that a few months ago. I have two identical furnaces in the house so I COULD test one furnace against the other but I would hate to end up with no heat at all. Any help or advice you could give me would be greatly appreciated. Thanks, in advance, for your consideration.
 
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Old 01-23-09, 06:29 AM
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Unfortunately, I get no listings for Goodman GVPS furnace when I do a search on the internet, and I can't recall that model furnace from memory. You might want to double check that model number on the rating plate of the furnace, found in the burner compartment.


Only a furnace with a standing pilot light would have a thermocouple --- and that's unlikely in a furnace from circa 1992.

I'm not saying you are wrong on these details, only that it would be worth double checking.

Since I can't identify much of anything about your furnace from the information you provided, I'll have to ask you to tell me more.

I'm presuming your furnace has a metal vent pipe to vent the combustion gasses, not PVC plastic pipe.

And I need to ask you to observe and report of the sequence of events that happens as you furnace lights up. You'd need to observe what's happening in the burner compartment from when the thermostat is turned up to when the blower fan comes on (if it does), and report what you see and hear happening. You might need to do that several times to notice all the subtle details.
 
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Old 01-23-09, 08:41 AM
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A 36C03 valve is definitely a 'Standing Pilot' valve, I believe a White Rogers. If you replaced the thermocouple and it was not a defective one, AND you tightened it up correctly at the valve, usually 1/4 to 1/2 turn after you feel significant resistance (WITH THE PILOT LIGHT OFF!) *never TIGHTEN A THERMOCOUPLE WHILE THE PILOT IS ON! The only thing left would be the safety circuit not permitting the valve to be energized.

In general the Goodman furnaces have red or orange safety circuit wiring and form a loop around the burner area. You will lose sight of the circuit where the modular plug is on the right side, but follow the wiring and see where all the roll-out sensors are. MOST of them will be non-resetable. If you shut down the e-switch for the furnace so that is is completely DEAD, you can check them out with a simple $12.00 meter from Radio Shack, or a continuity tester. Remove ONE wire from each of them and put the probes of the meter across the sensor. You should get a dead short when you do this. The are normally closed. As you confirm this put the wire back on. I think you will find a bad one. If you come across one with a little button on it between the connections, PUSH it in a couple of times to re-set it. Replace any ones you DO NOT get a reading on.

Goodmans have usually 3 around the burner assembly, one at the bottom, and one near the inducer fan by the smoke pipe. You will definitely find 3-5 sensors. Make sure that if you replace any to replace them with the exact one.

If you are familiar with electricity and circuits you can "jump out" with aligator clips one sensor to verify it is faulty, but do NOT leave it operating this way!!!!

If this does not find the problem check your 20-24 volt transformer with the meter. If you get at least 20 VAC to 24 VAC also check it out under load. Get TWO car bulbs 12 VAC and put them in series and hook them up to the 24 VAC output of the transformer to see if they light nicely. I have come across this problem on Goodmans where you are getting 22VAC but no real amps and it does not power the control circuit.
Good luck
 
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Old 01-23-09, 10:00 PM
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Sorry, I couldn't read my own handwriting. The model # is GUPS050-2. I did turn off the gas at the furnace gas valve as well as turning off the power before replacing the thermocoupler. This furnace has a metal pipe coming out of the furnace housing vertically directly above the inducer motor assembly.
Sequence of events:
1. turn up thermostat
2. about two seconds later inducer motor comes on
3. blower motor does not come on unless I force it to do so by changing the t-stat to ON as opposed to AUTO. blower motor will not come on at all in AUTO mode.
4. No other clicks or changes have been noted. Inducer motor behaves correctly: t-stat temp. up, inducer motor comes on/ t-stat temp.down, inducer motor goes off.
There is no ignition at the burners and no gas going to same. I blocked the gas jets (2) with my finger and no gas flow.
I believe the issue is electrical. I will check out the sensor issue and let you know what I found out. Thanks to both of you for the advice.
 
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Old 01-24-09, 08:05 AM
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You need to check the pressure switch and tubing to make sure it is clear and not cracked. You also need to clear the spud on the inducer that the tubing connects to. Use a drill bit or piece of wire.
 
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Old 01-24-09, 08:10 AM
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Originally Posted by Skip4661
You need to check the pressure switch and tubing to make sure it is clear and not cracked. You also need to clear the spud on the inducer that the tubing connects to. Use a drill bit or piece of wire.
Hmmmm. A furnace with an inducer motor and a standing pilot light. Haven't heard 'a that one before, but some further checking does confirm that.

I agree with Skip --- since the inducer motor is starting the next thing that should happen is that the pressure switch should close. You need to test to see that 24 VAC appears on both sides of the pressure switch after the inducer motor comes up to speed.
 
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Old 01-30-09, 08:09 AM
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I was kinda hinting towards tracing the control voltage on my previous post but things went off at a tangent with no positive results. So, trace out the safety circuit all the way around. BUT first, I would check to make sure your transformer is 'putting out' 20-24VAC with the amperage required to 'pull' the coil. I like the simple car bulb test, it works well for me! If the bulbs do not light real nice and bright, your transformer needs to be replaced. (I have found many times that even though you get a 24VAC reading on your meter, the transformer is not putting out any amperage, or little amperage is getting the the valve due to dirty connections, weak rollout sensor continuity, weak pressure switch continuity, etc.)

ALSO, before you invest in a new gas valve, for $150 or so, I would check the valve directly to see if it opens with the transformer in you unit. IF you are NOT familiar with this procedure, do not attemp it

I would also jump out the entire safety circuit to see if the valve goes on. This should be only a momentary test ( a few seconds) just to try to locate the fault.

Also check to see that your HIGH TEMP. sensor is not stuck open as this will NOT permit the burners to come on, but will allow the blower and on some units allow the inducer to come on during a start-up sequence.
 
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Old 01-31-09, 07:48 PM
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Talking

Originally Posted by Skip4661
You need to check the pressure switch and tubing to make sure it is clear and not cracked. You also need to clear the spud on the inducer that the tubing connects to. Use a drill bit or piece of wire.
You were right, Skip. The spud on the inducer motor housing was clogged with some type of debris. Thanks to all of you for your helpful advice. It is appreciated greatly. I haven't used this furnace all winter and I'm running out of firewood. The inducer motor housing has a fair amount of rust on the bottom. I found the roof vent was leaking rainwater and it found its way to the inducer motor housing. I picked up a new one yesterday and will install it tomorrow. Again, THANK YOU, THANK YOU, THANK YOU.
 
 

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