Voltages for Honeywell ST9120C


  #1  
Old 03-26-09, 05:50 PM
P
Member
Thread Starter
Join Date: Oct 2008
Location: Oklahoma
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Voltages for Honeywell ST9120C

I thought I had found the voltages for the Honeywell ST9120C Fan Timer board here, but maybe not. Anyone have a link?

I have a NG furnace that stopped lighting after an electrical storm. Inducer fan starts up a few seconds after thermostat calls for heat, but that's it, no HSI ignition or pilot valve opening.

Yes, it's the same furnace that had a defective smartvalve last October, so the timer is relatively new (ST9120C - 5013).

Im contemplating placing MOV's along the thermostat lines and the compressor line (that would have likely picked up some lightning energy) but unhappy that these expensive boards have so little transient protection.
Meanwhile, Id like to find the voltages to confirm whether it's the board or the smartvalve.
 
  #2  
Old 03-26-09, 06:30 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
St9120c

Figures 2 & 4 show the board used with a SmartValve.
http://customer.honeywell.com/techli...it/69-0781.pdf
 
  #3  
Old 03-27-09, 06:19 AM
C
Member
Join Date: Feb 2009
Location: Georgia
Posts: 86
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by patric
Inducer fan starts up a few seconds after thermostat calls for heat, but that's it, no HSI ignition or pilot valve opening.
hmmm.. is the pressure switch closing to allow for Ignition?
It would land 24V on the 24V Terminal of your INTERMITTENT
PILOT IGNITION MODULE. Put a meter on 24 GRND and 24V terminals of the intermittent pilot ignition module and see if you get 24 volts. If not it will never fire.
 
  #4  
Old 03-27-09, 05:01 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Intermittent Pilot Ignition Module

That furnace doesn't have such a module. It is incorporated into the SmartValve.
 
  #5  
Old 03-27-09, 05:45 PM
P
Member
Thread Starter
Join Date: Oct 2008
Location: Oklahoma
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by Grady
That furnace doesn't have such a module. It is incorporated into the SmartValve.
Correct, my Hot Surface Ignition (HSI) doesnt have the intermittent ignition connections, but...
I did get a reading of 28vac to ground on the smartvalve terminal identified as "24 volt thermostat or pressure switch" on the ST9120C installation sheet. I think that indicates pressure switch closure, correct?

PS Grady, thanks for the link but it times out, would it be expecting a logon?

Well, one reading down but no love (or heat) and expecting 2-4 inches snow tonight....
 
  #6  
Old 03-27-09, 06:05 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Link

Honeywell's site must be down. I just tried to get on & even the home page timed out. Darn it, wish I had printed that page.
I believe you are right in saying the 28v would indicate a pressure switch closure. Easy enough to check by actually testing at the pressure switch.
Have you checked continuity thru the ignitor?


Edit: 9:30PM Eastern, Honeywell's site is back up & the link works.

Have you checked to see if you are getting 24v to the ignitor?
Don't know if it will work or not but try a BBQ lighter on the pilot. If you can get pilot, maybe you can get main valve. Obviously this presumes something amiss with the ignitor or power to it.
 

Last edited by Grady; 03-27-09 at 06:34 PM.
  #7  
Old 03-27-09, 08:16 PM
P
Member
Thread Starter
Join Date: Oct 2008
Location: Oklahoma
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by Grady
Have you checked to see if you are getting 24v to the ignitor?
Don't know if it will work or not but try a BBQ lighter on the pilot. If you can get pilot, maybe you can get main valve. Obviously this presumes something amiss with the ignitor or power to it.
With reference to ground,
the 'EFT Output' is zero, and the
'24 volt hot' is 28 volts, as measured at the 4-pin smartvalve connector.

I didnt detect any clicks from the valve that might have indicated it was opening for pilot gas, nor did I smell any.

Something curious:
I turned the smartvalve's sliding switch to OFF, then began the start sequence, and about four seconds after the inducer motor came on the HSI ignitor began to glow.
If course no pilot or ignition, 'cause the smartvalve is turned off...
Turning the switch back on just kills the ignigtor.
 

Last edited by patric; 03-27-09 at 08:31 PM.
  #8  
Old 03-28-09, 01:24 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Inducer

You say the inducer only runs for a few seconds?
If so, that would seem to be a board problem unless there is voltage (120) being supplied to the inducer. If voltage is present I'd look at the inducer itself.
It also seems strange the HSI will get energized with the switch on the valve off but not when it's on????? You could have lost both the board & valve.
 
  #9  
Old 03-28-09, 08:44 PM
P
Member
Thread Starter
Join Date: Oct 2008
Location: Oklahoma
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by Grady
You say the inducer only runs for a few seconds?
If so, that would seem to be a board problem unless there is voltage (120) being supplied to the inducer. If voltage is present I'd look at the inducer itself.
It also seems strange the HSI will get energized with the switch on the valve off but not when it's on????? You could have lost both the board & valve.
The inducer starts a few seconds after the thermostat calls for heat and never stops.
Both the timer board and smartvalve were replaced in November, and are barely 4 months old.
 
  #10  
Old 03-29-09, 08:40 AM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Misunderstood

I misunderstood & thought the inducer was only running a few seconds. If it continues to run, at least that's one thing we don't have to worry about.

With no voltage on the EFT Output terminal, I leaning toward a board problem. I would expect 24v presuming the draft switch is closing, any limit switches are closed, & the roll out switch is closed.
 
  #11  
Old 03-29-09, 02:03 PM
P
Member
Thread Starter
Join Date: Oct 2008
Location: Oklahoma
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by Grady
With no voltage on the EFT Output terminal, I leaning toward a board problem. I would expect 24v presuming the draft switch is closing, any limit switches are closed, & the roll out switch is closed.
Is there an easy way to jumper the smartvalve to see if it still opens?
That way I would know whether or not to order a replacement for that when I order a new timer board.
 
  #12  
Old 03-29-09, 03:39 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
SmartValve

You might be able to apply 24v to the EFT Output terminal but I've never tried it. Which model SmartValve do you have? I'll see if I can find any technical info on it.
 
  #13  
Old 03-29-09, 09:17 PM
P
Member
Thread Starter
Join Date: Oct 2008
Location: Oklahoma
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by Grady
You might be able to apply 24v to the EFT Output terminal but I've never tried it. Which model SmartValve do you have? I'll see if I can find any technical info on it.
The SmartValve is SV9501 M2056
 
  #14  
Old 03-30-09, 07:28 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Sv9501

Figures 13 & 14 of this document might be of some help. http://customer.honeywell.com/techli...it/69-1004.pdf

Do not apply 24v to that EFT output terminal. That is an output from the SmartValve to the fan timer board.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: