View Full Version : Testing spark ignition module

Nov 17, 2007, 02:49 PM
Hi, I have an Armstrong hi-e furnace, that I suspect has a faulty spark module. (The blower control board, the gas valve, pilot, and spark device are all new). The module is a Honeywell S8660k. The manual says to test the spark at the module. Can anyone tell me how to go about that? The lead to the spark device is a pretty thin wire, but it says it is 30,000 volts, so I want to be sure.
Any other tips on testing the module would be appreciated.

Nov 17, 2007, 07:41 PM
Use a high voltage tester. Most heating service men have one.

Nov 17, 2007, 07:44 PM
Do you have voltage going to the spark ignitor and if so what is it? Make sure the electrode is not grounded out, but make sure the spark ignition control box is grounded to the equipment.

Nov 17, 2007, 08:42 PM
Hi, There is a lead going to the module which goes through a switch which is connected to vacuum (?) lines from the burner air fan and the gas valve. There is no power going through that switch at startup, but I did jumper that switch and try startup, but still no go. The voltage is 24. Grounds are good.
Would a Fluke meter handle that spark output? If so, do I just connect one lead to the contact and ground the other lead?
Thanks again

Nov 19, 2007, 08:29 AM
First thing, DO NOT USE YOUR VOLTMETER TO CHECK THE SPARK VOLTAGE!! You will only do that once, and smoke your meter by the 8,000 volts from the S86 control RESPECT this voltage! It works like this. 1. turn your gas supply off to your unit, start the call for heat, and with your volt meter check across the control at 24 volt and ground terminals, you must have 24 VOLT power feeding the contol during the start cycle, if you don't find out why not and correct that issue. 2. With the power turned off to your unit, take off the spark wire from the spark electrode, push back the rubber boot to expose the metal connector end, and with a pair of INSULATED handle pliers, hold that high voltage wire within about a 1/4 to 1/8 inch or closer to any ground screw on the metal part of your unit, and turn on the power... with a call for heat... if the control is good it will now draw a strong spark to that screw or metal surface. The problem is usually the control, but could be a bad spark (high voltage wire) and /or the electrode bad, with a dirty and or cracked ceramic insulator... BE SURE to make yourself a drawing of the color wires going to which connection on the control, so you don't have a issue installing the new control... good luck... tsa7man

Nov 19, 2007, 12:20 PM
Hi, Thanks for the advice. As I noted before there is a switch mounted on a device which has a vacuum (air line) line going to it, which is connected via tubing to a port on the induced draft fan housng, as well as to a port on the gas valve, and a little port up in the corner of the fire box. With power on, there is 24v. Going to one side of that switch. The other side of that switch goes to the ignition module, and there is no power going through that switch. I did jumper both sides of that switch, providing 24 v. to the module, but still no activity to the spark electrodes that I can detect. The spark assy. Is brand new, borrowed from another unit, so there should be no problem there. The assy. With the vacuum lines attached is a circlar shaped device, about 3/4" thich, and about 2.5" diameter, with the 24 v. switch mounted on it's side. It is bolted to the front of the furnace heat exchange box, but I don't believe there is any other connection to the inside of the heat exchanger (i.e. a sensor). Could someone explain to me what the function of this device is? It doesn't seem that there would be much air pressure anywhere here. Other controls are a small sensor mounted against the top of the fire box, which has a little plastic spade protruding out of it, which appears to be some sort of switch, as it can be depressed. The other remaining item, which is not new is a sensor which goes into the heat exchange box. I have swapped this with a borrowed one, but neither changes the no-spark situation.
Thanks again, in advance.

Nov 19, 2007, 01:10 PM
The pressure swith is a safety device to insure air flow through the unit... you will need to jumper across the switch connections to only by-pass it for a test, then check to see if you have power to the control... which now you should, so if that is your problem, it is either a bad pressure switch or you really have an air flow problem, and the safety switch is really do it's job... post back your findings...

Nov 19, 2007, 01:13 PM
Another thing to check, take off the rubber hose to that pressure switch (remove it completely), and blow through it to see if any water is in it... then check the connection on the blower side to be sure that tube connection is clear... not plugged up with rust if that is a metal connection for the hose... then put it all back together and test the unit again...

Nov 19, 2007, 01:15 PM
Also, how many wires are going to that switch?

Nov 19, 2007, 01:24 PM
John, post the full model number to the furnace... Ken (tsa7man)

Nov 19, 2007, 04:25 PM
Hi Ken, The furnace is an Armstrong Ultra SX 90 (upflow).
Mod# GUK125D20-1A Serial# 8493611595.
I haven't checked all of the air passages for clear flow yet. There had been issues with the cup on the bottom of the intake pipe filliing with water, and I had modified it with a nipple in the bottom of the cup routed outside to let the condensation run to the floor.
I had jumpered that switch, and I think I checked to find current to the module. I'll do it again, and check to see if I get a spark, as was previously suggested.
I'll check those hoses when I get home tonight, and let you know what I find.
Thanks again, John

Nov 20, 2007, 02:28 PM
Hi Ken, Happy to report that the furnace has been running as of this morning. I sort of hate to admit it, but the final problem turned out to be a faulty splice in the thermostat wire. I don't know how we missed it before - I don't think it developed since we've been checking it, but I'm not quite sure how it was missed. I guess we had 24 v. at the transformer, and I'd swear we had 24 v. at the furnace end of the thermostat connnections. There have been 4 brains at work here on the problem, 2 brothers, my father, and yours truly. Well, aside from having heat, I've learned quite a bit about the furnace operation that I didn't know before.
Thanks so much for all the help and pointers. This is a fantastic resource.
All the best, and Happy Thanksgiving wishes,