Gas Furnace Spark Ignition Troubleshooting- Mercury Flame Sensor!

[@acservicetechchannel]

Tool List- www.amazon.com/shop/acservicetech Support- www.patreon.com/acservicetech For those that are looking for the tools used in the videos: (Linked Below) Here is a link to the UEI DL389 Multimeter used in the videos- amzn.to/2av8s3q Here is the link to the Fieldpiece SDMN6 Dual Pressure Testing Manometer with Pump-amzn.to/2jyK5Ka Here is a link for the Supco Magnet Jumpers amzn.to/2gS4h6z Here is the link for the Irwin Wire Stripper/Cutter/Crimper amzn.to/2dGTj2V Other tool links can be found in the video description section. ACSERVICETECH is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.

[@Frank_Techguy]

You are an excellent instructor. Your explanation for this setup is to the point and concise. The live demo really helps.

[@bobparker9511]

Excellent! I'm a mechanic and I have this set up on my residential boiler. I understand thermocouples and while trying to diag my problem got stumped. Your video was a "moment of discovery " for me! You are a very sharp young man. Thanks for sharing your knowledge.

[@jimbola77]

excellent thank you for sharing words can't explain how much I appreciate you sharing your professional knowledge!!!!!

[@acservicetechchannel]

Thank you very much jimbola77!

[@SombraLocs]

Great teacher! You have so much knowledge. Thanks for sharing.

[@acservicetechchannel]

Thank you very much Familia Sanchez HVAC!

[@ib1r.41]

Seen something similar the other day, Montgomery Ward pkage unit. Had this switch, mercury style. Had 2 terminals labeled pilot from trans. to maybe spark ig.? Gas valve wired with pilot switch. Question is, should the trans. provide voltage to ignitor in order to spark gas? I didn't hear spark and turned on flame with a long ignitor. Hopefully get some answer.

[@Pauladigms]

How sensitive is the mercury tube to fouling? Trying nto find a more robust technology that can deal with the siloxanes put out by biogas. What has been your experience with them needing to be cleaned, etc.?

[@PaulHVAC1]

Very very good video. Hats off to you sir :)

[@acservicetechchannel]

Thank you very much Paul HVAC!

[@timburns9754]

Great video. I just finished “fixing” my Weil-McLain VHE-3 that had this issue. The odd part is that I’m not sure what I fixed. The system was working fine. I then cleaned it up (vacuumed and dusted the system pretty thoroughly for the first time in a while). Then I could not get it to work. It seemed like the pilot light was sufficient and the mercury flame sensor was engulfed in the pilot flame, but it was not heating up enough to switch positions to get the main burners to come on. The house was kind of cold, so I made a fire in a wood burning stove near by. Now the system is functioning properly. I’m not sure if there was too much heat loss from the pilot light end to the switch end of the mercury flame sensor. It seems counterintuitive to have to raise the temperature of the system to get it to turn on the first time. Do you have any thoughts or have you seen this before? Thanks.

[@7jack7]

Just came across one of these in a rooftop furnace/AC unit. Someone along the way converted it to a standing pilot, probably because the old sparker died. The mercury switch was in the flame 24/7/365. Apparently the constant pressure caused by being constantly immersed in flame caused the mercury cavity to expand enough over he years to weaken the pressure on the diaphram. In very cold temperatures there was not enough pressure to close the switch that opens the main burner. I figure the stainless steel tube was acting like a radiator to cool the mercury. Took me ten visits to track down the problem. I finally was able to catch it when it was cold enough to cause it to fail to open the main burner while I was there with a meter. I read 28 volts going in to the mercury switch and nothing coming out to the main gas valve. One thing I don't quite understand is what closes the pilot valve after the main burner ignites. On this system there were only two wires going to the gas valve. They had to be opening both the main and pilot valves simultaneously. Can't see how only two wires can control them independently. Perhaps on this older system the pilot stays lit as long as the main gas flows. Thanks for clearing up the mystery.

[@capitolrefrigerationheatin7501]

I had this setup in a old carrier rtu and the supply house told me parts are not available anymore because of the mercury. I had to buy the part used off ebay, I didnt know you could retrofit a newer ignition.

[@acservicetechchannel]

Here is a link to one but you certainly can still get these. The supply houses may or may not still carry stock though but could get them next day likely. This is a link to one but you need to check the round connector positions, amoiunt of connections and sensor length though -- amzn.to/2kyGcmb

[@capitolrefrigerationheatin7501]

thank you,i did not know about that!

[@luistrejo8804]

So if all the conditions are made will this open up the main burners ?

[@acservicetechchannel]

The flame would heat the mercury sensor which would be stage one for the pilot and 24v would power the main stage for the main burner, thanks!

[@danieldummett3731]

Hello again. Off topic to this video, I have one question that I really can't seem to wrap my head around. Hopefully you can bring some closure to this, I don't know if you may have answered it in an older video so please bare with me. So my question is regarding the w1,w2 and y1,y2 terminals on the thermostat. I know they have to do with two stage heating and cooling, but here is the thing. For example, the Lennox furnaces I have mostly been working on we just wire the heating to the w1 and then the furnace control board has a set time with the dip switches I believe before second stage kicks in. So when would I ever use w2? I just finally got a job in service 2 months ago and haven't even touched on the cooling side yet so if you do reply focus more on the w2 use, but I would still like to know when the y2 for cooling is used as well. Sorry about what is probably a very silly question, I have just yet to see it used so i'm curious. Thanks in advance. I started watching your vids about 2 weeks now starting from the oldest and working my way up. skipped to the most recent so you would see this comment haha. Keep up the amazing work. Hope to hear from you.

[@acservicetechchannel]

Most newer boards over the last 15 years give you the option of controlling when 1st and 2nd speed would run. Simply put though, it is almost always more efficient to allow the board to decide when to run in either speed. This is what it sounds like you are doing which is good. The big thing is that installers a lot of times don't do is set dip switches so on furnaces you service, take a peak at the dip switches and look up what they should be depending on the manufacturer. Y1 and Y2 are for two speed outdoor ac and heat pump units so if you have a single speed unit then you should only wire the one then. If you have a two speed thermostat and you have two wires to the furnace then just leave that unless you go into the program or change to a single speed thermostat. You could also jump the w1 and w2 of a gas furnace heat terminals at the thermostat and disconnect the one at the thermostat and act as if it is just a single speed stat and wire the furnace as you have been with the one wire. I hope that helps! Thanks Daniel!

[@danieldummett3731]

acservicetech you rock. Thanks man.

[@acservicetechchannel]

Glad to help Daniel!

[@Fleebee459]

Can the mercury bulb be heated up enough to get the switch to active using a hot air gun? I have replaced the switching assembly but I'm concerned I might have put in another bad switch... Great vid BTW. Thanks!

[@acservicetechchannel]

I haven't tried myself. I would think it would be hot enough though

[@patlysobey1938]

@@acservicetechchannel I use a propane torch. I don't know about the hot air gun because the bulb end actually gets red hot.

[@jamesdetzel5035]

Thank you very much for this very informative video! I hope that you still are monitoring feedback. Here is my dilemma, Utica boiler with a WR 36c84 GV, 3098-134 merc flame sensor. Have been having intermittent problems with the spark, GV, and duration of boiler being fired. I bit the bullet and bought a new GV and flame sensor. Changed it all out. Now having problem with pilot. Spark is good but no gas to pilot! Can hear gas vale click, but no gas to pilot. Put all old GV and flame sensor back and now am getting intermittent pilot gas. Question: What is causing the pilot gas valve to be hanging up? Any help would be great, getting to the point that I almost am bald with all the hair I've pulled out. Thanks!

[@patlysobey1938]

I have a similar WR gas valve and mercury flame sensor that is triggered by the pilot flame. The pilot portion of the gas valve is opened by a solenoid on the gas valve. You can put a metal ruler on the solenoid to see if there is magnetic field pulling the pilot valve open. You may have a blockage of some sort inside the gas valve but you swapped out a new one and it didn't work at all. You should check your incoming gas line pressure because that would cause your WR gas valve to not function properly. My pilot operates okay but it sometimes has trouble triggering the mercury flame switch to open the main gas valve. As long as the pilot flame is on, I occassionly remove the mercury sensor and jumper the terminals with a #12 U-shaped wire to open the main gas valve and when the mercury switch clicks over I replace the jumper with the mercury flame sensor plug and the boiler operates as normal. I hope this helps

[@acservicetechchannel]

Hey James, there could be a clog at the orifice of the pilot tube. Did you check the inlet gas pressure? Can you adjust the pilot flame itself some with a pilot adjustment screw so the rod gets more heat? Is the pilot head warped or not quite lined up with the mercury rod? Thanks James and Pat!

[@waynemiles7027]

How many volts did you say that spark igniter was and is that AC or DC current.Thanks.

[@acservicetechchannel]

That is AC.and on this ignitor, I believe it is around 6,000 volts. Thanks

[@majcaboose]

give your light guy a bonus

[@acservicetechchannel]

Thanks Dan!

[@3GreeneBJ]

Almost invisible spark