Goodman Janitrol Furnace - no voltage at gas valve

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  #1  
Old 01-22-16, 09:38 AM
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Goodman Janitrol Furnace - no voltage at gas valve

Goodman/Janitrol HVAC
Model: GMP075-3

No error codes.

The vent motor starts, but I am not getting 24V at the gas valve.
All 4 rollout switches are tested closed.

Any tips of what to look at next?

Thanks
Steve
 
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  #2  
Old 01-22-16, 09:59 AM
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Maybe not sensing that the inducer is running. Check the pressure switch. There's also an auxiliary switch on the schematic....maybe a door switch.
 
  #3  
Old 01-22-16, 10:14 AM
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Thanks for the tip.
I thought the inducer wouldn't continue to run if the vent pressure switch is open, and I am getting no status light flashes. But the VPS should be easy to check.

I see the same "S0" in the schematic, but I can't find a physical switch. The wire from the controller to the first rollout switch does not have 24V on it either. I do have continuity through the rollout switches from the controller to the gas valve.

I am considering swapping the upstairs and downstairs controllers to see if the problem follows the controller. Both are ICM-280 controllers.

Again, thanks for the tip.

Offhand, this unit is more than 20 years old, so I may consider just doing a replacement. What is a ballpark guess what I should plan to pay for a HVAC guy to replace it?

Thanks, Steve
 
  #4  
Old 01-22-16, 10:28 AM
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As long as the stat calls for heat the inducer blower will run.
 
  #5  
Old 01-22-16, 10:51 AM
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Almost there.
The Vent Pressure Switch works when I gently suck on the tube. I did this and clamped the tube to maintain the vacuum and the furnace works normally.

There appears to be no suction coming from the hose fitting on the blower. At least I can't feel any with my finger.

So, do I just use a toothpick to clean the fitting or do I have to take the vent fan assembly apart?
 
  #6  
Old 01-22-16, 11:21 AM
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toothpick or a small drill bit works well to make sure the little opening is clear all the way into housing. Shouldn't have to take it apart.
 
  #7  
Old 01-22-16, 11:31 AM
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Thanks so much - I owe you a six-pack. It seems to be working now. I don't know if the switch was simply stuck or if the orifice was clogged, but it is working now.

I am wondering if I shouldn't just go ahead and replace the switch or wait for it to fail again...
 
  #8  
Old 01-22-16, 12:00 PM
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Good to hear

One of the other moderators here said in another thread a week or two ago that it's common for the orifice to get clogged.
 
  #9  
Old 01-22-16, 01:30 PM
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<<One of the other moderators here said in another thread a week or two ago that it's common for the orifice to get clogged.>>



Yes, it's fairly common for the access fitting on the inducer motor housing to get plugged up with corrosion since it's exposed to the combustion gasses of the furnace.

I'd find a small drill bit that serves to clean out that fitting, and leave it on the furnace so the fitting can be cleaned out every year or two as routine maintenance.

Don't bother replacing the pressure switch, which only quite rarely goes bad.
 
  #10  
Old 01-23-16, 12:39 PM
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Just to add a closing note to this thread..... I don't recommend using a toothpick to clean the orifice. Use a small drill bit or paper clip. It's too easy to break the tip of the toothpick off and having it jammed in the hole.
 
  #11  
Old 01-24-16, 02:02 PM
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<<Just to add a closing note to this thread..... I don't recommend using a toothpick to clean the orifice. Use a small drill bit or paper clip. >>


I agree.

Personally, I favor a small drill bit, but perhaps a paper clip is small enough to work commonly.


The key is being SURE that you get your cleaning device well into the inducer motor housing. On some furnace, there is a smaller hole inside the inducer motor port that you need to get through. Just getting into the outer hole visible on the exterior of the fitting isn't enough.
 
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