It has been a long time since I worked on a gas furnace. My sister and Brother in law have no heat. They have had a ongoing problem with the thermostat, and I think it needs to probably be replaced. It is a Honeywell 50018270-001. I want to Jump it out, and see if I can get it to fire. The problem is I do not remember if it is red to white. Here is the wires that are currently hooked up. White (W) Yellow (Y) Green (G) O-No wire RC-No wire R-Red Wire B-No Wire C-Blue (optional with batteries)
Also let me add, If I am correct the red wire is the 24 volt, and white would be the furnace, yellow would be the Ac, and the Green would be the fan. I am not sure though about blue, is that just the common wire?
Correct. Red=your 24v source White=heating circuit Yellow=cooling circuit Green=blower motor (fan) C (common)=In a 5-wire configuration, typically blue. In an 8-wire configuration, sometimes black. Just make sure its the same on the equipment (furnace) terminals and T-stat terminals. The electrons really don't care what color insulation the wiring has!
Ok thank you, I should just be able to connect the red to white and the gas furnace should fire correct? No need to turn off power before you connect them since it is just 24 volts?
There is always the risk of blowing the fuse on the circuit board of the furnace if you don't shut the power off to the furnace first. Putting a Jumper wire between R and W will indeed fire the furnace...and keep it running forever...until the jumper wire is removed. That's what the T-stat is for.
24v will still give you a tingle-enough for you to react quickly to it. Are you trying to wire the T-stat? Yes, shut the power off to the furnace, then back on after you wire the T-stat.
Thank you for your help, like I said it has been a while since I worked on a furnace. It was a family member that was having problems and before I walked my brother in law through the troubleshooting, I wanted to make sure I was correct. It is still not fixed yet, but I believe there going to have someone come back out. They had a tech there a month or two ago and said the thermostat froze, the tech messed with it, charged them 100 bucks and left.
It is weird, after he jumped it, it still did not fire. He called me this evening and said now the AC and The fan will come on, just not the heat! I wish I could get up there and look at to see what Is going on with my own eyes! As far as voltage goes, I have done some wiring so it does not bother me, but you definitely have to respect it that is for sure! I will never forget a time I got hit by 240, not sure how I made it, but that is when I learned to respect it.
Keep us updated. It may be furnace related. Any gas smells? Take the burner tubes out, clean them, and see what else you are working with. I've replaced a few Honeywell ignition modules over the years.
I've had thermostats do a lot of weird things and for the money it's generally easiest to replace them if they're more than 5 years old, before calling the repair guy. That said it sounds like jumping it didn't do the trick so now you're way deeper into troubleshooting mode. I'd jump it right at the furnace to rule out the thermostat wiring and also have the ability to watch and listen to what the furnace is doing. Is it lighting the pilot or does the spark or ignitor rod seem to be doing it's thing? If the pilot is lit can you hear the main gas valve turn on? If the main burner lights does the plenum heat up and then the blower doesn't come on (plenum snap switch failure in which case it will go into overheat and shutdown again)? Probably all stuff you already know to look at if you were there in person but that's my quick and dirty troubleshooting.
A furnace won't light if the venting is plugged. Whenever there is a larger snowstorm, homeowners should clear the snow away from the vent pipes to prevent clogging and freezing. This applies to high efficiency furnaces. PVC pipes out the side of the house, typically. In "snow belt" areas, installers normally keep the terminations of said pipes one foot above anticipated snow depth. Have they received more snow than usual?
#1 cause of no burner on the more modern furnaces is the sail switch - located in the forced exhaust stream- if that switch does not close no ignition or gas valve operation. #2 is the pilot orifice which over time will become blocked by crud easy to clean by removing and a little wire brush work on the outside and a needle to make sure the pilot orifice is not plugged. # 3 is the thermocouple that is in the pilot flame when it gets hot enough it allows current to the gas valve for the main burner. As you haven't stated the style of furnace can't go much further. Older style furnace with spark or standing pilot are similar in operation sans the sail switch mostly a combination of the thermocouple and pilot failures. Also the spark units will go in to a wait mode if the unit doesn't light, time length varies some as high as 10 minutes before you can retry the ignition sequence. This is a safety feature top prevent gas build up in the furnace and a resulting explosion. Hope this provides some help.
Thanks guys for the help, no snow block, but the condensate was plugged, causing the failure to ignite!
Sorry, I should have suggested that at the same time I posted about the venting. Were they without heat for very long?
No big deal, they were only down for 1 day, but they have a gas fireplace to help take the chill off! Thanks again for all your help!
