No 24v to Main Gas Valve Solenoid, 2nd stage. - http://www.hvacmechanic.com/ Forums
Original message
| MatthewJM
 |  "No 24v to Main Gas Valve Solenoid, 2nd stage."
, posted Sat 9 Feb 14:55  
I have an American Standard Furnace Freedom 80 Comfort-R.
The Main Gas Valve Solenoid does not energize, no 24volts from the "Pressure switch 2nd stage". [referencing the diagram on inside door panel].
The "lo fire" 1st stage solenoid ALWAYS gets 24v after pilot light is on for 20 seconds.
The "hi fire" 2nd stage solenoid does not get 24v from the "Pressure switch 2nd stage"
[Sometimes, the Main Gas Valve, 2nd stage, does get 24v and the burner comes on.]
Can you offer any advice or can you direct me to where I can get further information on:
Why am I not getting 24v from the "Pressure Switch 2nd stage" to 2nd stage solenoid?
As I've said, very seldom it will work as designed and the burner will come on ,,, THEN it will stop working, no 24v to 2nd stage solenoid.
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Replies:
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| justsomeguy
| "Re(1):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 15:28
Either the inducer motor is not pulling the correct amperage at second stage or the pressure switch is failing. You could also have something stuck in the inducer motor that is causing it not to turn at the correct rpm when second stage is called.
BillyBob
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| | MatthewJM
| "Re(2):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 16:55
Thank you for the input.
I've replaced the "2 Stage Gas Valve Assembly" [both solenoids]. The strange thing is it worked OK for 2 weeks. Then the same problem returned.
I've traced the 24v wire from the "1st stage solenoid" back to the controller board. It gets 24 volts after pilot light is on for 20 seconds.
I've traced the 24v wire from the "2nd stage solenoid" back to the controller board. It never gets 24 volts.
I don't know if "2nd stage solenoid" gets its 24v DIRECTLY from controller board [like "1st stage solenoid"] -or- if it gets 24v from the "Pressure switch" ???
KNOWING THAT ANSWER WOULD HELP MY TROUBLESHOOTING.
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| | justsomeguy
| "Re(3):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 17:55
How does the schematic say that the second stage switch is wired? It should be in series with the first stage switch. If it is then it gets voltage from the first stage switch. Check your voltage at the switch like this: Put one probe on ground, Check voltage at each side of the first stage switch, there should be voltage on both sides with reference to ground. When/if you hear the inducer motor ramp up and hear/see the burners fire at a greater rate than they initially do then the second stage is calling. This takes about ten minutes on your furnace. When the second stage calls, again with one lead on ground check on both sides of the second stage switch. If you have voltage on both sides then the switch works, if you have voltage on only one side then the unit did not call the second stage (bad board, thermostat not 2 stage or not wired for 2 stage), the switch is defective, the inducer motor is not ramping up when the call for second stage happens or you have a restriction in the flue pipe. If your thermostat is not 2 stage then you can put a jumper wire across w1 and w2 at the control board. This will cause the system to call the second stage, usually this will take ten minutes on your system.
BillyBob
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| | MatthewJM
| "Re(4):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 18:33
Thanks JustSomeGuy,,, but I don't think I have the furnace you are referencing, I could be wrong -- BUT THERE IS NO 10 MINUTE CYCLE! All activity happens within 3 minutes !
You can see MY FURNACE here:
http://www.americanstandardair.com/HomeOwner/Products/Furnaces/Freedom80CR.aspx
My Furnace DOES NOTHING after two RE-tries at igniting the burner. After two re-tries it gives an error code "Re-tries Exceeded" which takes about 3 minutes in TOTAL !!! Then it just sits there with the exhaust fan running.
Both solenoids share the same "COMMON", labeled as such and attached to the Controller Board.
The 2nd stage solenoid "hot" wire goes to a tab on the "Pressure Switch 2nd Stage", from that SAME TAB, it then goes to the Controller Board "Pressure Switch Input". [The other tab on the "Pressure Switch 2nd Stage" goes to the Controller Board "Gas Valve High 2nd Stage". With my multimeter it shows 24v only for a moment when pilot light first comes on.]
The 1st stage solenoid "hot" wire goes directly to the Controller Board "Gas Valve Low 1st Stage".
THE TWO SOLENOIDS ARE NOT WIRED IN SERIES.
Again, everything happens within 3 minutes, there is no "after" 10 minute activity.
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| | static
| "Re(5):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 21:36
Argh.
Can you post a picture(s) of the inside of your furnace? And the flue pipe? These pressure switches are connected to the same vacuum tube, are they not? I'd like to see some pics, I think they'd help, thanks.
SIGNATURE -- I smell something burning...
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| | MatthewJM
| "Re(6):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 22:14
Sorry I forgot to answer your second question !!!
Yes, the pressure switch "combo" [it has 2 wires on back side and 2 wires on front side] is connected to one vacuum tube. The vacuum tube is transparent and very clean looking.
As for the "flue pipe" ,,, I'm not that knowledgeable on furnace apparatus [parts]. I'm learning as we go along !!! I have no idea how to recognize a flue ??? What does it connect to and what is its purpose, please ???
Much thanks
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| | static
| "Re(7):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 22:47
Okay, with one tube feeding both switches if you disconnect that hose then the furnace will stop whatever it's doing. It has to have at least one of those "made" to even think about firing.
The flue pipe is the 4" metal pipe coming from the top of the furnace, going to the chimney.
Is there only one pressure switch in there, that does both low and high fire?? Huh, haven't seen that arrangement yet.
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| | MatthewJM
| "Re(6):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 22:05
Yes I can post a picture IF I knew how ???
I don't see anything on this web page like "attachment" or "image" ???
I have no idea HOW TO POST a picture in this forum ???
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| | MatthewJM
| "Re(7):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 23:57
I took a closer look at the Pressure Switch. There are 2 Pressure Switches "piggy-back" [connected to one another]. Only one Pressure Switch has a hose connected to it "Pressure Switch 2nd Stage" which is mounted in front. There are 2 wires connected to each Pressure Switch; 2 wires in front and 2 wires in back.
I took 5 pictures. If they are too dark let me know and I will try again. The garage is kinda dark right now with no sunlight.
My username is MJMolinaJr
I'm new to this so I don't know if you will be able to see my images ???
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| | static
| "Re(7):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 22:42
You have to upload it to a place like www.imageshack.us or www.photobucket.com . Copy the link for "direct link to image" and paste in to your post. Be sure to wrap "IMG" tags at either end of the link, using the square brackets[]. Like this:
{img}www.imageshack/nameofpicture.soandso157{/img}. But use the square brackets [] instead of the ones I just used {}.
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| | MatthewJM
| "Re(8):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sun 10 Feb 00:03
I don't think that worked. I don't see the URL posted. I used the brackets and slash just like your example. Do I need a slash at the beginning also ???
[/img]http://s252.photobucket.com/albums/hh34/MJMolinaJr/[/img]
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| | static
| "Re(9):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sun 10 Feb 01:20:
After further review, this is what I think.
IIRC, the furnace starts out in high fire for just a second in order to prove both pressure switches, then drops to low fire...could be wrong on that, but that would explain the voltage present at the high pressure switch, which goes away when the ignitor comes on...once the furnace has initially proven the high pressure switch, it no longer cares what that switch is doing, for the time being.
Please make sure that hose isn't kinked, and stick a sewing needle into the metal tit on the collector box that hose attaches to, to make sure it isn't obstructed.
Number one thing that keeps the pressure switch from closing on an 80% furnace is a bird or other obstruction stuck in the flue pipe or chimney. Please check for that.
(Click on the image to play)
A short video clip of what the vacuum in the furnace does during the ignition sequence. Note how far it pulls down at the moment the burners fire. Anything restricting the flue or the metal tit will reduce the amount of vacuum available further still. The high pressure switch has a higher vacuum requirement to close than does the low pressure switch.
You could always just have a bad pressure switch...it does happen occasionally.
Good luck and good night.
[this message was edited by static on Sun 10 Feb 01:23] |
| | MatthewJM
| "Re(10):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sun 10 Feb 10:42
Thank you very very much. - I will try everything you said and POST my results.
Checking for a bird or something in the flue pipe & chimney sounds promising !!!
Your "video clip of what the vacuum in the furnace does" will help ME understand the PURPOSE and OPERATION of this very important piece of equipment [the PRESSURE SWITCH] !!!
I would make one comment on your thoughts before I implement your suggestions ,,, "You could always just have a bad pressure switch." - Would not the Diagnostic Code [flashing light] flash 3 times signaling PRESSURE SWITCH ERROR, if the pressure switch were malfunctioning ??? Just a thought.
Again thank you, I will do everything you suggest !!!
P.S. An aside - When I had my microwave worked on [a Maytag with an electrical failure] the seasoned veteran serviceman told me their #1 "problem call" is a varmint in the exhaust vent !!! :-)
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| | static
| "Re(2):Re(10):No 24v to Main Gas Valve Solenoi" , posted Sun 10 Feb 12:16
Lol, I hadn't even thought about the fault codes...my bad.
Well, with your voltmeter, you can check that the pressure switch is closing, you will see a reading of 24 volts across the terminals when it's open and 0 volts when it's closed. The inducer should ramp up first, then the high fire pressure switch should close. Then the second stage of the gas valve should come on. If the pressure switch is closing and the Hi terminal on the gas valve never gets energized with 24 volts, I would probably begin to get suspicious of a control board problem. Sorry for not mentioning that last night,
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| | MatthewJM
| "Re(3):Re(10):No 24v to Main Gas Valve Solenoi" , posted Sun 10 Feb 17:56
static, I have much data but no answers :-( ,,, I hope you can provide some. I did everything you suggested.
- Vacuum Hose to collector box test:
The vacuum hose to the collector box has NO kinks or abrasions; it is transparent and looks new.
- Collector Box tit test:
The metal tit on the collector box has NO obstruction inside it. It is large and easily checked.
- Flue Pipe test:
I removed completely the flue pipe to the chimney. Looking down I could see a clean squirrel cage and surrounding area. Looking up I could clearly see sunlight, NO obstructions.
- "Pressure Switch 2nd Stage" test:
1. Voltmeter probes across switch; Thermostat heat on; Plug in Furnace; 1 volt shown on meter.
2. click, clicks heard
3. 24 volts on voltmeter for an instant then back to 1 volt.
4. Then Pilot Light comes on for 20 seconds.
5. click, click heard.
6. Voltmeter NEVER changed from 1 volt.
NOTE: Keep in mind there is NO VOLTAGE applied to the 2nd Stage Pressure Switch EVER except for the moment BEFORE pilot Light comes on [I measured it.] -- I believe this 2nd Stage Pressure Switch NEVER CLOSES, is ALWAYS OPEN [NO voltage applied].
- "Pressure Switch 1st Stage" test:
1. Voltmeter probes across switch; Thermostat heat on; Plug in Furnace; 0 volts shown on meter.
2. click, clicks heard
3. VOLTS shown on voltmeter for an instant then back to 0 volts.
4. Then Pilot Light comes on for 20 seconds.
5. click, click heard.
6. Voltmeter NEVER changed from 0 volts.
NOTE: Keep in mind THERE IS 24 volts APPLIED to the 1st Stage Pressure Switch throughout the start cycle [I measured it.] -- I believe this 1st Stage Pressure Switch IS working PROPERLY.
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| | MatthewJM
| "Re(4):Re(10):No 24v to Main Gas Valve Solenoi" , posted Sun 10 Feb 19:45
Thanks static for all your help. I've decided to replace the Pressure Switch. It's not that expensive.
My Multi-meter measurements tell me that the 2nd Stage Pressure Switch is NEVER closing. I'm thinking it should be closing JUST LIKE THE 1st Stage Pressure Switch is closing. [That's with my very limited knowledge on proper furnace operation. [Lo side .17" WCPF, Hi side .50" WCPF] You said the 2nd Stage requires MORE vacuum !!! But that begs the question ,,, WHY??? is there no Diagnostic Code signifying the Malfunction of the Pressure Switch ??? It definitely ain't closing !!! I KNOW IT AIN'T CLOSING SO WHERE'S THE DIAGNOSTIC CODE "3" ???
I don't know. That's where my limited knowledge fails me again !!! [Maybe it's lousy programming code on the Control Board?]
Irregardless ,,, if this doesn't fix it ,,, I'll be looking harder at replacing the Control Board !!!
Thanks again,
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| | MatthewJM
| "Re(3):Re(10):No 24v to Main Gas Valve Solenoi" , posted Sun 10 Feb 14:33
MOST EXCELLENT - Your tip on troubleshooting the Pressure Switch!!!
"Better late than never" !!! I always say !!! :-)
I will try everything you suggest !!!
Much Thanks ,,, and I will POST results !!!
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| bubbad
| "Re(1):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 15:22
Are you getting a call for 2nd stage heat when the gas valve is not energizing? Do you have a 2 stage thermostat? If you only have a single stage thermostat, there may be a jumper/dip switch which selects a timer for 2nd stage operation.
If it's running in low fire, and you get the call for high fire, the the inducer motor should go to high speed, then the 2nd stage pressure switch will make, (provided there is no flue/obstruction problem), and then the gas valve will switch to high, followed by high speed indoor blower.
bubbad
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| | MatthewJM
| "Re(2):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 17:07
Thank you for the input. I'm not sure how to answer your question, sorry.
I can say this under NORMAL OPERATION:
1st the pilot light comes on for 20 seconds.
2nd I hear a SOFT CLICK [nothing is observed].
3rd [one second later] I hear a LOUD click.
4th [two seconds later] burner comes on.
I've replaced the "2 Stage Gas Valve Assembly" [both solenoids]. The strange thing is it worked OK for 2 weeks. Then the same problem returned.
I've traced the 24v wire from the "1st stage solenoid" back to the controller board. It gets 24 volts after pilot light is on for 20 seconds.
I've traced the 24v wire from the "2nd stage solenoid" back to the controller board. [It shares a tab at the "Pressure Switch 2nd Stage]. It never gets 24 volts when burner fails to light.
I don't know if "2nd stage solenoid" gets its 24v DIRECTLY from controller board [like the "1st stage solenoid"] -or- if it gets 24v from the "Pressure switch" tab ???
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| static
| "Re(1):No 24v to Main Gas Valve Solenoid, 2nd " , posted Sat 9 Feb 15:21
Sounds like perhaps there's not enough vacuum being generated to engage the high fire pressure switch.
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| | MatthewJM
| "Re(2):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 17:09
Thanks for the reply.
Can you elaborate a little more ??? How can I determine if the problem is my Controller Board or my Pressure Switch 2nd stage ???
I can say this under NORMAL OPERATION:
1st the pilot light comes on for 20 seconds.
2nd I hear a SOFT CLICK [nothing is observed].
3rd [one second later] I hear a LOUD click.
4th [two seconds later] burner comes on.
I've replaced the "2 Stage Gas Valve Assembly" [both solenoids]. The strange thing is it worked OK for 2 weeks. Then the same problem returned.
I've traced the 24v wire from the "1st stage solenoid" back to the controller board. It gets 24 volts after pilot light is on for 20 seconds.
I've traced the 24v wire from the "2nd stage solenoid" back to the controller board. [It shares a tab at the "Pressure Switch 2nd Stage]. It never gets 24 volts when burner fails to light.
I don't know if "2nd stage solenoid" gets its 24v DIRECTLY from controller board [like the "1st stage solenoid"] -or- if it gets 24v from the "Pressure switch" tab ???
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| | MatthewJM
| "Re(3):No 24v to Main Gas Valve Solenoid, 2nd" , posted Sat 9 Feb 18:03
Thanks Static,
I DON'T THINK IT'S "not enough vacuum being generated to engage the high fire pressure switch" because if I disconnect the "vacuum hose" ,,, the pilot light does not come on and the furnace does nothing at all. I could be wrong ,,, can I troubleshoot the "pressure switch" further ???
How can I determine if it's the Controller Board failing ???
The "high fire pressure switch" has 24v on the wire going to Controller Board but it immediately goes to zero when the pilot light comes on ???
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